It would appear that any change in the habits of life, whatever these

habits may be, if great enough, tends to affect in an inexplicable manner

the powers of reproduction. The result {160} depends more on the

constitution of the species than on the nature of the change; for certain

whole groups are affected more than others; but exceptions always occur,

for some species in the most fertile groups refuse to breed, and some in

the most sterile groups breed freely. Those animals which usually breed

freely under confinement, rarely breed, as I was assured, in the Zoological

Gardens, within a year or two after their first importation. When an animal

which is generally sterile under confinement happens to breed, the young

apparently do not inherit this power; for had this been the case, various

quadrupeds and birds, which are valuable for exhibition, would have become

common. Dr. Broca even affirms[385] that many animals in the Jardin des

Plantes, after having produced young for three or four successive

generations, become sterile; but this may be the result of too close

interbreeding. It is a remarkable circumstance that many mammals and birds

have produced hybrids under confinement quite as readily as, or even more

readily than, they have procreated their own kind. Of this fact many

instances have been given;[386] and we are thus reminded of those plants

which when cultivated refuse to be fertilised by their own pollen, but can

easily be fertilised by that of a distinct species. Finally, we must

conclude, limited as the conclusion is, that changed conditions of life

have an especial power of acting injuriously on the reproductive system.

The whole case is quite peculiar, for these organs, though not diseased,

are thus rendered incapable of performing their proper functions, or

perform them imperfectly.

_Sterility of Domesticated Animals from changed conditions._--With

respect to domesticated animals, as their domestication mainly depends

on the accident of their breeding freely under captivity, we ought not

to expect that their reproductive system would be affected by any

moderate degree of change. Those orders of quadrupeds and birds, of

which the wild species breed most readily in our menageries, have

afforded us the greatest number of domesticated productions. Savages in

most parts of the world are fond of taming animals;[387] and if any of

these regularly produced {161} young, and were at the same time useful,

they would be at once domesticated. If, when their masters migrated

into other countries, they were in addition found capable of

withstanding various climates, they would be still more valuable; and

it appears that the animals which breed readily in captivity can

generally withstand different climates. Some few domesticated animals,

such as the reindeer and camel, offer an exception to this rule. Many

of our domesticated animals can bear with undiminished fertility the

most unnatural conditions; for instance, rabbits, guinea-pigs, and

ferrets breed in miserably confined hutches. Few European dogs of any

kind withstand without degeneration the climate of India; but as long

as they survive, they retain, as I hear from Mr. Falconer, their

fertility; so it is, according to Dr. Daniell, with English dogs taken

to Sierra Leone. The fowl, a native of the hot jungles of India,

becomes more fertile than its parent-stock in every quarter of the

world, until we advance as far north as Greenland and Northern Siberia,

where this bird will not breed. Both fowls and pigeons, which I

received during the autumn direct from Sierra Leone, were at once ready

to couple.[388] I have, also, seen pigeons breeding as freely as the

common kinds within a year after their importation from the Upper Nile.

The guinea-fowl, an aboriginal of the hot and dry deserts of Africa,

whilst living under our damp and cool climate, produces a large supply

of eggs.

Nevertheless, our domesticated animals under new conditions

occasionally show signs of lessened fertility. Roulin asserts that in

the hot valleys of the equatorial Cordillera sheep are not fully

fecund;[389] and according to Lord Somerville,[390] the merino-sheep

which he imported from Spain were not at first perfectly fertile. It is

said[391] that mares brought up on dry food in the stable, and turned

out to grass, do not at first breed. The peahen, as we have seen, is

said not to lay so many eggs in England as in India. It was long before

the canary-bird was fully fertile, and even now first-rate breeding

birds are not common.[392] In the hot and dry province of Delhi, the

eggs of the turkey, as I hear from Dr. Falconer, though placed under a

hen, are extremely liable to fail. According to Roulin, geese taken

within a recent period to the lofty plateau of Bogota, at first laid

seldom, and then only a few eggs; of these scarcely a fourth were

hatched, and half the young birds died: in the second generation they

were more fertile; and when Roulin wrote they were becoming as {162}

fertile as our geese in Europe. In the Philippine Archipelago the

goose, it is asserted, will not breed or even lay eggs.[393] A more

curious case is that of the fowl, which, according to Roulin, when

first introduced would not breed at Cusco in Bolivia, but subsequently

became quite fertile; and the English Game fowl, lately introduced, had

not as yet arrived a its full fertility, for to raise two or three

chickens from a nest of eggs was thought fortunate. In Europe close

confinement has a marked effect on the fertility of the fowl: it has

been found in France that with fowls allowed considerable freedom only

twenty per cent. of the eggs failed; when allowed less freedom forty

per cent. failed; and in close confinement sixty out of the hundred

were not hatched.[394] So we see that unnatural and changed conditions

of life produce some effect on the fertility of our most thoroughly

domesticated animals, in the same manner, though in a far less degree,

as with captive wild animals.

It is by no means rare to find certain males and females which will not

breed together, though both are known to be perfectly fertile with

other males and females. We have no reason to suppose that this is

caused by these animals having been subjected to any change in their

habits of life; therefore such cases are hardly related to our present

subject. The cause apparently lies in an innate sexual incompatibility

of the pair which are matched. Several instances have been communicated

to me by Mr. W. C. Spooner (well known for his essay on

Cross-breeding), by Mr. Eyton of Eyton, by Mr. Wicksted and othe

breeders, and especially by Mr. Waring of Chelsfield, in relation to

horses, cattle, pigs, foxhounds, other dogs, and pigeons.[395] In these

cases, females, which either previously or subsequently were proved to

be fertile, failed to breed with certain males, with whom it was

particularly desired to match them. A change in the constitution of the

female may sometimes have occurred before she was put to the second

male; but in other cases this explanation is hardly tenable, for a

female, known not to be barren, has been unsuccessfully paired seven or

eight times with the same male likewise known to be perfectly fertile.

With cart-mares, which sometimes will not breed with stallions of pure

blood, but subsequently have bred with cart-stallions, Mr. Spooner is

inclined to attribute the failure to the lesser sexual power of the

race-horse. But I have heard from the greatest breeder of race-horses

at the present day, through Mr. Waring, that "it frequently occurs with

a mare to be put several times during one or two seasons to a

particular stallion of acknowledged power, and yet prove barren; the

mare afterwards breeding at once with some other horse." These facts

are worth recording, as they show, like so many previous facts, on what

slight constitutional differences the fertility of an animal often

depends.

{163}

_Sterility of Plants from changed Conditions of Life, and from other

causes._

In the vegetable kingdom cases of sterility frequently occur, analogous

with those previously given in the animal kingdom. But the subject is

obscured by several circumstances, presently to be discussed, namely, the

contabescence of the anthers, as Gaertner has named a certain

affection--monstrosities--doubleness of the flower--much-enlarged

fruit--and long-continued or excessive propagation by buds.

It is notorious that many plants in our gardens and hot-houses, though

preserved in the most perfect health, rarely or never produce seed. I

do not allude to plants which run to leaves, from being kept too damp,

or too warm, or too much manured; for these do not produce the

reproductive individual or flower, and the case may be wholly

different. Nor do I allude to fruit not ripening from want of heat, or

rotting from too much moisture. But many exotic plants, with their

ovules and pollen appearing perfectly sound, will not set any seed. The

sterility in many cases, as I know from my own observation, is simply

due to the absence of the proper insects for carrying the pollen to the

stigma. But after excluding the several cases just specified, there are

many plants in which the reproductive system has been seriously

affected by the altered conditions of life to which they have been

subjected.

It would be tedious to enter on many details. Linnaeus long ago

observed[396] that Alpine plants, although naturally laded with seed,

produce either few or none when cultivated in gardens. But exceptions

often occur: the _Draba sylvestris_, one of our most thoroughly Alpine

plants, multiplies itself by seed in Mr. H. C. Watson's garden, near

London; and Kerner, who has particularly attended to the cultivation of

Alpine plants, found that various kinds, when cultivated, spontaneously

sowed themselves.[397] Many plants which naturally grow in peat-earth

are entirely sterile in our gardens. I have noticed the same fact with

several liliaceous plants, which nevertheless grew vigorously.

Too much manure renders some kinds utterly sterile, as I have myself

observed. The tendency to sterility from this cause runs in families;

thus, according to Gaertner,[398] it is hardly possible to give too

much manure to most Gramineae, Cruciferae, and Leguminosae, whilst

succulent and bulbous-rooted plants are easily affected. Extreme

poverty of soil is less {164} apt to induce sterility; but dwarfed

plants of _Trifolium minus_ and _repens_, growing on a lawn often mown

and never manured, did not produce any seed. The temperature of the

soil, and the season at which plants are watered, often have a marked

effect on their fertility, as was observed by Koelreuter in the case of

Mirabilis.[399] Mr. Scott in the Botanic Gardens of Edinburgh observed

that _Oncidium divaricatum_ would not set seed when grown in a basket

in which it throve, but was capable of fertilisation in a pot where it

was a little damper. _Pelargonium fulgidum_, for many years after its

introduction, seeded freely; it then became sterile; now it is

fertile[400] if kept in a dry stove during the winter. Other varieties

of pelargonium are sterile and others fertile without our being able to

assign any cause. Very slight changes in the position of a plant,

whether planted on a bank or at its base, sometimes make all the

difference in its producing seed. Temperature apparently has a much

more powerful influence on the fertility of plants than on that of

animals. Nevertheless it is wonderful what changes some few plants will

withstand with undiminished fertility: thus the _Zephyranthes candida_,

a native of the moderately warm banks of the Plata, sows itself in the

hot dry country near Lima, and in Yorkshire resists the severest

frosts, and I have seen seeds gathered from pods which had been covered

with snow during three weeks.[401] _Berberis Wallichii_, from the hot

Khasia range in India, is uninjured by our sharpest frosts, and ripens

its fruit under our cool summers. Nevertheless I presume we must

attribute to change of climate the sterility of many foreign plants;

thus the Persian and Chinese lilacs (_Syringa Persica_ and

_Chinensis_), though perfectly hardly, never here produce a seed; the

common lilac (_S. vulgaris_) seeds with us moderately well, but in

parts of Germany the capsules never contain seed.[402]

Some of the cases, given in the last chapter, of self-impotent plants,

which are fertile both on the male and female side when united with

distinct individuals or species, might have been here introduced; for

as this peculiar form of sterility generally occurs with exotic plants

or with endemic plants cultivated in pots, and as it disappeared in the

_Passiflora alata_ when grafted, we may conclude that in these cases it

is the result of the treatment to which the plants or their parents

have been exposed.

The liability of plants to be affected in their fertility by slightly

changed conditions is the more remarkable, as the pollen when once in

process of formation is not easily injured; a plant may be

transplanted, or a branch with flower-buds be cut off and placed in

water, and the pollen will be matured. Pollen, also, when once mature,

may be kept for weeks or even months.[403] The female organs are more

sensitive, for Gaertner[404] found that dicotyledonous plants, when

carefully removed so that they did not in the least flag, could seldom

be fertilised; this occurred even with potted {165} plants if the roots

had grown out of the hole at the bottom. In some few cases, however, as

with Digitalis, transplantation did not prevent fertilisation; and

according to the testimony of Mawz, _Brassica rapa_, when pulled up by

its roots and placed in water, ripened its seed. Flower-stems of

several monocotyledonous plants when cut off and placed in water

likewise produce seed. But in these cases I presume that the flowers

had been already fertilised, for Herbert[405] found with the Crocus

that the plants might be removed or mutilated after the act of

fertilisation, and would still perfect their seeds; but that, if

transplanted before being fertilised, the application of pollen was

powerless.

Plants which have been long cultivated can generally endure with

undiminished fertility various and great changes; but not in most cases

so great a change of climate as domesticated animals. It is remarkable

that many plants under these circumstances are so much affected that

the proportions and the nature of their chemical ingredients are

modified, yet their fertility is unimpaired. Thus, as Dr. Falconer

informs me, there is a great difference in the character of the fibre

in hemp, in the quantity of oil in the seed of the Linum, in the

proportion of narcotin to morphine in the poppy, in gluten to starch in

wheat, when these plants are cultivated on the plains and on the

mountains of India; nevertheless, they all remain fully fertile.

_Contabescence._--Gaertner has designated by this term a peculiar

condition of the anthers in certain plants, in which they are

shrivelled, or become brown and tough, and contain no good pollen. When

in this state they exactly resemble the anthers of the most sterile

hybrids. Gaertner,[406] in his discussion on this subject, has shown

that plants of many orders are occasionally thus affected; but the

Caryophyllaceae and Liliaceae suffer most, and to these orders, I

think, the Ericaceae may be added. Contabescence varies in degree, but

on the same plant all the flowers are generally affected to nearly the

same extent. The anthers are affected at a very early period in the

flower-bud, and remain in the same state (with one recorded exception)

during the life of the plant. The affection cannot be cured by any

change of treatment, and is propagated by layers, cuttings, &c., and

perhaps even by seed. In contabescent plants the female organs are

seldom affected, or merely become precocious in their development. The

cause of this affection is doubtful, and is different in different

cases. Until I read Gaertner's discussion I attributed it, as

apparently did Herbert, to the unnatural treatment of the plants; but

its permanence under changed conditions, and the female organs not

being affected, seem incompatible with this view. The fact of several

endemic plants becoming contabescent in our gardens seems, at first

sight, equally incompatible with this view; but Koelreuter believes

that this is the result of their transplantation. The contabescent

plants of Dianthus and Verbascum, found wild by Wiegmann, grew on a dry

and sterile bank. The fact that exotic {166} plants are eminently

liable to this affection also seems to show that it is in some manner

caused by their unnatural treatment. In some instances, as with Silene,

Gaertner's view seems the most probable, namely, that it is caused by

an inherent tendency in the species to become dioecious. I can add

another cause, namely, the illegitimate unions of reciprocally

dimorphic or trimorphic plants, for I have observed seedlings of three

species of Primula and of _Lythrum salicaria_, which had been raised

from plants illegitimately fertilised by their own-form pollen, with

some or all their anthers in a contabescent state. There is perhaps an

additional cause, namely, self-fertilisation; for many plants of

Dianthus and Lobelia, which had been raised from self-fertilised seeds,

had their anthers in this state; but these instances are not

conclusive, as both genera are liable from other causes to this

affection.

Cases of an opposite nature likewise occur, namely, plants with the

female organs struck with sterility, whilst the male organs remain

perfect. _Dianthus Japonicus_, a Passiflora, and Nicotiana, have been

described by Gaertner[407] as being in this unusual condition.

_Monstrosities as a cause of Sterility._--Great deviations of

structure, even when the reproductive organs themselves are not

seriously affected, sometimes cause plants to become sterile. But in

other cases plants may become monstrous to an extreme degree and yet

retain their full fertility. Gallesio, who certainly had great

experience,[408] often attributes sterility to this cause; but it may

be suspected that in some of his cases sterility was the cause, and not

the result, of the monstrous growths. The curious St. Valery apple,

although it bears fruit, rarely produces seed. The wonderfully

anomalous flowers of _Begonia frigida_, formerly described, though they

appear fit for fructification, are sterile.[409] Species of Primulae,

in which the calyx is brightly coloured, are said[410] to be often

sterile, though I have known them to be fertile. On the other hand,

Verlot gives several cases of proliferous flowers which can be

propagated by seed. This was the case with a poppy, which had become

monopetalous by the union of its petals.[411] Another extraordinary

poppy, with the stamens replaced by numerous small supplementary

capsules, likewise reproduces itself by seed. This has also occurred

with a plant of _Saxifraga geum_, in which a series of adventitious

carpels, bearing ovules on their margins, had been developed between

the stamens and the normal carpels.[412] Lastly, with respect to

peloric flowers, which depart wonderfully from the natural

structure,--those of _Linaria vulgaris_ seem generally to be more or

less sterile, whilst those before described of _Antirrhinum majus_,

when artificially fertilised with their own pollen, are perfectly {167}

fertile, though sterile when left to themselves, for bees are unable to

crawl into the narrow tubular flower. The peloric flowers of _Corydalis

solida_, according to Godron,[413] are barren; whilst those of Gloxinia

are well known to yield plenty of seed. In our greenhouse Pelargoniums,

the central flower of the truss is often peloric, and Mr. Masters

informs me that he tried in vain during several years to get seed from

these flowers. I likewise made many vain attempts, but sometimes

succeeded in fertilising them with pollen from a normal flower of

another variety; and conversely I several times fertilised ordinary

flowers with peloric pollen. Only once I succeeded in raising a plant

from a peloric flower fertilised by pollen from a peloric flower borne

by another variety; but the plant, it may be added, presented nothing

particular in its structure. Hence we may conclude that no general rule

can be laid down; but any great deviation from the normal structure,

even when the reproductive organs themselves are not seriously

affected, certainly often leads to sexual impotence.

_Double Flowers._--When the stamens are converted into petals, the

plant becomes on the male side sterile; when both stamens and pistils

are thus changed, the plant becomes completely barren. Symmetrical

flowers having numerous stamens and petals are the most liable to

become double, as perhaps follows from all multiple organs being the

most subject to variability. But flowers furnished with only a few

stamens, and others which are asymmetrical in structure, sometimes

become double, as we see with the double gorse or Ulex, Petunia, and

Antirrhinum. The Compositae bear what are called double flowers by the

abnormal development of the corolla of their central florets.

Doubleness is sometimes connected with prolification,[414] or the

continued growth of the axis of the flower. Doubleness is strongly

inherited. No one has produced, as Lindley remarks,[415] double flowers

by promoting the perfect health of the plant. On the contrary,

unnatural conditions of life favour their production. There is some

reason to believe that seeds kept during many years, and seeds believed

to be imperfectly fertilised, yield double flowers more freely than

fresh and perfectly fertilised seed.[416] Long-continued cultivation in

rich soil seems to be the commonest exciting cause. A double narcissus

and a double _Anthemis nobilis_, transplanted into very poor soil, have

been observed to become single;[417] and I have seen a completely

double white primrose rendered permanently single by being divided and

transplanted whilst in full flower. It has been observed by Professor

Morren that doubleness of the flowers and variegation of the leaves are

antagonistic states; but so many exceptions to the rule have lately

been recorded,[418] that, though general, it cannot be looked at as

invariable. {168} Variegation seems generally to result from a feeble

or atrophied condition of the plant, and a large proportion of the

seedlings raised from parents both of which are variegated usually

perish at an early age; hence we may perhaps infer that doubleness,

which is the antagonistic state, commonly arises from a plethoric

condition. On the other hand, extremely poor soil sometimes, though

rarely, appears to cause doubleness: I formerly described[419] some

completely double, bud-like, flowers produced in large numbers by

stunted wild plants of _Gentiana amarella_ growing on a poor chalky

bank. I have also noticed a distinct tendency to doubleness in the

flowers of a Ranunculus, Horse-chesnut, and Bladder-nut (_Ranunculus

repens_, _Aesculus pavia_, and _Staphylea_), growing under very

unfavourable conditions. Professor Lehman[420] found several wild

plants growing near a hot spring with double flowers. With respect to

the cause of doubleness, which arises, as we see, under widely

different circumstances, I shall presently attempt to show that the

most probable view is that unnatural conditions first give a tendency

to sterility, and that then, on the principle of compensation, as the

reproductive organs do not perform their proper functions, they either

become developed into petals, or additional petals are formed. This

view has lately been supported by Mr. Laxton,[421] who advances the

case of some common peas, which, after long-continued heavy rain,

flowered a second time, and produced double flowers.

_Seedless Fruit._--Many of our most valuable fruits, although

consisting in a homological sense of widely different organs, are

either quite sterile, or produce extremely few seeds. This is

notoriously the case with our best pears, grapes, and figs, with the

pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms, and

some members of the orange-tribe. Poorer varieties of these same fruits

either habitually or occasionally yield seed.[422] Most horticulturists

look at the great size and anomalous development of the fruit as the

cause, and sterility as the result; but the opposite view, as we shall

presently see, is more probable.

_Sterility from the excessive development of the Organs of Growth or

Vegetation._--Plants which from any cause grow too luxuriantly, and

produce leaves, stems, runners, suckers, tubers, bulbs, &c., in excess,

sometimes do not flower, or if they flower do not yield seed. To make

European vegetables under the hot climate of India yield seed, it is

necessary to check their growth; and, when one-third grown, they are

taken up, and their stems and {169} tap-roots are cut or

mutilated.[423] So it is with hybrids; for instance, Prof. Lecoq[424]

had three plants of Mirabilis, which, though they grew luxuriantly and

flowered, were quite sterile; but after beating one with a stick until

a few branches alone were left, these at once yielded good seed. The

sugar-cane, which grows vigorously and produces a large supply of

succulent stems, never, according to various observers, bears seed in

the West Indies, Malaga, India, Cochin China, or the Malay

Archipelago.[425] Plants which produce a large number of tubers are apt

to be sterile, as occurs, to a certain extent, with the common potato;

and Mr. Fortune informs me that the sweet potato (_Convolvulus

batatas_) in China never, as far as he has seen, yields seed. Dr. Royle

remarks[426] that in India the _Agave vivipara_, when grown in rich

soil, invariably produces bulbs, but no seeds; whilst a poor soil and

dry climate leads to an opposite result. In China, according to Mr.

Fortune, an extraordinary number of little bulbs are developed in the

axils of the leaves of the yam, and this plant does not bear seed.

Whether in these cases, as in those of double flowers and seedless

fruit, sexual sterility from changed conditions of life is the primary

cause which leads to the excessive development of the organs of

vegetation, is doubtful; though some evidence might be advanced in

favour of this view. It is perhaps a more probable view that plants

which propagate themselves largely by one method, namely by buds, have

not sufficient vital power or organised matter for the other method of

sexual generation.

Several distinguished botanists and good practical judges believe that

long-continued propagation by cuttings, runners, tubers, bulbs, &c.,

independently of any excessive development of these parts, is the cause

of many plants failing to produce flowers and of others failing to

produce fertile flowers,--it is as if they had lost the habit of sexual

generation.[427] That many plants when thus propagated are sterile

there can be no doubt, but whether the long continuance of this form of

propagation is the actual cause of their sterility, I will not venture,

from the want of sufficient evidence, to express an opinion.

That plants may be propagated for long periods by buds, without the aid

of sexual generation, we may safely infer from this being the case with

many plants which must have long survived in a state of nature. As I

have had occasion before to allude to this subject, I will here give

such cases as I have collected. Many alpine plants ascend mountains

beyond the height at which they can produce seed.[428] Certain species

of {170} Poa and Festuca, when growing on mountain-pastures, propagate

themselves, as I hear from Mr. Bentham, almost exclusively by bulblets.

Kalm gives a more curious instance[429] of several American trees,

which grow so plentifully in marshes or in thick woods, that they are

certainly well adapted for these stations, yet scarcely ever produce

seeds; but when accidentally growing on the outside of the marsh or

wood, are loaded with seed. The common ivy is found in Northern Sweden

and Russia, but flowers and fruits only in the southern provinces. The

_Acorus calamus_ extends over a large portion of the globe, but so

rarely perfects its fruit that this has been seen but by few

botanists.[430] The _Hypericum calycinum_, which propagates itself so

freely in our shrubberies by rhizomas and is naturalised in Ireland,

blossoms profusely, but sets no seed; nor did it set any when

fertilised in my garden by pollen from plants growing at a distance.

The _Lysimachia nummularia_, which is furnished with long runners, so

seldom produces seed-capsules, that Prof. Decaisne,[431] who has

especially attended to this plant, has never seen it in fruit. The

_Carex rigida_ often fails to perfect its seed in Scotland, Lapland,

Greenland, Germany, and New Hampshire in the United States.[432] The

periwinkle (_Vinca minor_), which spreads largely by runners, is said

scarcely ever to produce fruit in England;[433] but this plant requires

insect-aid for its fertilisation, and the proper insects may be absent

or rare. The _Jussiaea grandiflora_ has become naturalised in Southern

France, and has spread by its rhizomas so extensively as to impede the

navigation of the waters, but never produces fertile seed.[434] The

horse-radish (_Cochlearia armoracia_) spreads pertinaciously and is

naturalised in various parts of Europe; though it bears flowers, these

rarely produce capsules: Professor Caspary also informs me that he has

watched this plant since 1851, but has never seen its fruit; nor is

this surprising, as he finds scarcely a grain of good pollen. The

common little _Ranunculus ficaria_ rarely, and some say never, bears

seed in England, France, or Switzerland; but in 1863 I observed seeds

on several plants growing near my house. According to M. Chatin, there

are two forms of this Ranunculus; and it is the bulbiferous form which

does not yield seed from producing no pollen.[435] Other cases {171}

analogous with the foregoing could be given; for instance, some kinds

of mosses and lichens have never been seen to fructify in France.

Some of these endemic and naturalised plants are probably rendered

sterile from excessive multiplication by buds, and their consequent

incapacity to produce and nourish seed. But the sterility of others

more probably depends on the peculiar conditions under which they live,

as in the case of the ivy in the northern parts of Europe, and of the

trees in the swamps of the United States; yet these plants must be in

some respects eminently well adapted for the stations which they

occupy, for they hold their places against a host of competitors.

Finally, when we reflect on the sterility which accompanies the doubling of

flowers,--the excessive development of fruit,--and a great increase in the

organs of vegetation, we must bear in mind that the whole effect has seldom

been caused at once. An incipient tendency is observed, and continued

selection completes the work, as is known to be the case with our double

flowers and best fruits. The view which seems the most probable, and which

connects together all the foregoing facts and brings them within our

present subject, is, that changed and unnatural conditions of life first

give a tendency to sterility; and in consequence of this, the organs of

reproduction being no longer able fully to perform their proper functions,

a supply of organised matter, not required for the development of the seed,

flows either into these same organs and renders them foliaceous, or into

the fruit, stems, tubers, &c., increasing their size and succulency. But I

am far from wishing to deny that there exists, independently of any

incipient sterility, an antagonism between the two forms of reproduction,

namely, by seed and by buds, when either is carried to an extreme degree.

That incipient sterility plays an important part in the doubling of

flowers, and in the other cases just specified, I infer chiefly from the

following facts. When fertility is lost from a wholly different cause,

namely, from hybridism, there is a strong tendency, as Gaertner[436]

affirms, for flowers to become double, and this tendency is inherited.

Moreover it is notorious that with hybrids the male organs become sterile

before the female organs, and with double flowers the stamens first become

{172} foliaceous. This latter fact is well shown by the male flowers of

dioecious plants, which, according to Gallesio,[437] first become double.

Again, Gaertner[438] often insists that the flowers of even utterly sterile

hybrids, which do not produce any seed, generally yield perfect capsules or

fruit,--a fact which has likewise been repeatedly observed by Naudin with

the Cucurbitaceae; so that the production of fruit by plants rendered

sterile through any other and distinct cause is intelligible. Koelreuter

has also expressed his unbounded astonishment at the size and development

of the tubers in certain hybrids; and all experimentalists[439] have

remarked on the strong tendency in hybrids to increase by roots, runners,

and suckers. Seeing that hybrid plants, which from their nature are more or

less sterile, thus tend to produce double flowers; that they have the parts

including the seed, that is the fruit, perfectly developed, even when

containing no seed; that they sometimes yield gigantic roots; that they

almost invariably tend to increase largely by suckers and other such

means;--seeing this, and knowing, from the many facts given in the earlier

parts of this chapter, that almost all organic beings when exposed to

unnatural conditions tend to become more or less sterile, it seems much the

most probable view that with cultivated plants sterility is the exciting

cause, and double flowers, rich seedless fruit, and in some cases

largely-developed organs of vegetation, &c., are the indirect

results--these results having been in most cases largely increased through

continued selection by man.

* * * * *

{173}

CHAPTER XIX.

SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.

ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON

FERTILITY--CLOSE INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED

CONDITIONS OF LIFE--VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON

THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND

VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON

HYBRIDISM BY THE ILLEGITIMATE PROGENY OF DIMORPHIC AND TRIMORPHIC

PLANTS--STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE

REPRODUCTIVE SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS

WHY DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS

BEEN LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND

CROSSED VARIETIES--CONCLUSION.

It was shown in the fifteenth chapter that when individuals of the same

variety, or even of a distinct variety, are allowed freely to intercross,

uniformity of character is ultimately acquired. Some few characters,

however, are incapable of fusion, but these are unimportant, as they are

almost always of a semi-monstrous nature, and have suddenly appeared.

Hence, to preserve our domesticated breeds true, or to improve them by

methodical selection, it is obviously necessary that they should be kept

separate. Nevertheless, through unconscious selection, a whole body of

individuals may be slowly modified, as we shall see in a future chapter,

without separating them into distinct lots. Domestic races have often been

intentionally modified by one or two crosses, made with some allied race,

and occasionally even by repeated crosses with very distinct races; but in

almost all such cases, long-continued and careful selection has been

absolutely necessary, owing to the excessive variability of the crossed

offspring, due to the principle of reversion. In a few instances, however,

mongrels have retained a uniform character from their first production.

When two varieties are allowed to cross freely, and one is {174} much more

numerous than the other, the former will ultimately absorb the latter.

Should both varieties exist in nearly equal numbers, it is probable that a

considerable period would elapse before the acquirement of a uniform

character; and the character ultimately acquired would largely depend on

prepotency of transmission, and on the conditions of life; for the nature

of these conditions would generally favour one variety more than another,

so that a kind of natural selection would come into play. Unless the

crossed offspring were slaughtered by man without the least discrimination,

some degree of unmethodical selection would likewise come into action. From

these several considerations we may infer, that when two or more closely

allied species first came into the possession of the same tribe, their

crossing will not have influenced, in so great a degree as has often been

supposed, the character of the offspring in future times; although in some

cases it probably has had a considerable effect.

Domestication, as a general rule, increases the prolificness of animals and

plants. It eliminates the tendency to sterility which is common to species

when first taken from a state of nature and crossed. On this latter head we

have no direct evidence; but as our races of dogs, cattle, pigs, &c., are

almost certainly descended from aboriginally distinct stocks, and as these

races are now fully fertile together, or at least incomparably more fertile

than most species when crossed, we may with much confidence accept this

conclusion.

Abundant evidence has been given that crossing adds to the size, vigour,

and fertility of the offspring. This holds good when there has been no

previous close interbreeding. It applies to the individuals of the same

variety but belonging to different families, to distinct varieties,

sub-species, and partially even to species. In the latter case, though size

is often gained, fertility is lost; but the increased size, vigour, and

hardiness of many hybrids cannot be accounted for solely on the principle

of compensation from the inaction of the reproductive system. Certain

plants, both of pure and hybrid origin, though perfectly healthy, have

become self-impotent, apparently from the unnatural conditions to which

they have been exposed; and such plants, as well as others in their normal

state, can be stimulated to {175} fertility only by crossing them with

other individuals of the same species or even of a distinct species.

On the other hand, long-continued close interbreeding between the nearest

relations diminishes the constitutional vigour, size, and fertility of the

offspring; and occasionally leads to malformations, but not necessarily to

general deterioration of form or structure. This failure of fertility shows

that the evil results of interbreeding are independent of the augmentation

of morbid tendencies common to both parents, though this augmentation no

doubt is often highly injurious. Our belief that evil follows from close

interbreeding rests to a large extent on the experience of practical

breeders, especially of those who have reared many animals of the kinds

which can be propagated quickly; but it likewise rests on several carefully

recorded experiments. With some animals close interbreeding may be carried

on for a long period with impunity by the selection of the most vigorous

and healthy individuals; but sooner or later evil follows. The evil,

however, comes on so slowly and gradually that it easily escapes

observation, but can be recognised by the almost instantaneous manner in

which size, constitutional vigour, and fertility are regained when animals

that have long been interbred are crossed with a distinct family.

These two great classes of facts, namely, the good derived from crossing,

and the evil from close interbreeding, with the consideration of the

innumerable adaptations throughout nature for compelling, or favouring, or

at least permitting, the occasional union of distinct individuals, taken

together, lead to the conclusion that it is a law of nature that organic

beings shall not fertilise themselves for perpetuity. This law was first

plainly hinted at in 1799, with respect to plants, by Andrew Knight,[440]

and, not long afterwards, that sagacious observer Koelreuter, after showing

how well the Malvaceae are adapted for {176} crossing, asks, "an id aliquid

in recessu habeat, quod hujuscemodi flores nunquam proprio suo pulvere, sed

semper eo aliarum suae speciei impregnentur, merito quaeritur? Certe natura

nil facit frustra." Although we may demur to Koelreuter's saying that

nature does nothing in vain, seeing how many organic beings retain

rudimentary and useless organs, yet undoubtedly the argument from the

innumerable contrivances, which favour the crossing of distinct individuals

of the same species, is of the greatest weight. The most important result

of this law is that it leads to uniformity of character in the individuals

of the same species. In the case of certain hermaphrodites, which probably

intercross only at long intervals of time, and with unisexual animals

inhabiting somewhat separated localities, which can only occasionally come

into contact and pair, the greater vigour and fertility of the crossed

offspring will ultimately prevail in giving uniformity of character to the

individuals of the same species. But when we go beyond the limits of the

same species, free intercrossing is barred by the law of sterility.

In searching for facts which might throw light on the cause of the good

effects from crossing, and of the evil effects from close interbreeding, we

have seen that, on the one hand, it is a widely prevalent and ancient

belief that animals and plants profit from slight changes in their

condition of life; and it would appear that the germ, in a somewhat

analogous manner, is more effectually stimulated by the male element, when

taken from a distinct individual, and therefore slightly modified in

nature, than when taken from a male having the same identical constitution.

On the other hand, numerous facts have been given, showing that when

animals are first subjected to captivity, even in their native land, and

although allowed much liberty, their reproductive functions are often

greatly impaired or quite annulled. Some groups of animals are more

affected than others, but with apparently capricious exceptions in every

group. Some animals never or rarely couple: some couple freely, but never

or rarely conceive. The secondary male characters, the maternal functions

and instincts, are occasionally affected. With plants, when first subjected

to cultivation, analogous facts have been observed. We probably owe our

double flowers, rich seedless {177} fruits, and in some cases greatly

developed tubers, &c., to incipient sterility of the above nature combined

with a copious supply of nutriment. Animals which have long been

domesticated, and plants which have long been cultivated, can generally

withstand with unimpaired fertility great changes in their conditions of

life; though both are sometimes slightly affected. With animals the

somewhat rare capacity of breeding freely under confinement has mainly

determined, together with their utility, the kinds which have been

domesticated.

We can in no case precisely say what is the cause of the diminished

fertility of an animal when first captured, or of a plant when first

cultivated; we can only infer that it is caused by a change of some kind in

the natural conditions of life. The remarkable susceptibility of the

reproductive system to such changes,--a susceptibility not common to any

other organ,--apparently has an important bearing on Variability, as we

shall see in a future chapter.

It is impossible not to be struck with the double parallelism between the

two classes of facts just alluded to. On the one hand, slight changes in

the conditions of life, and crosses between slightly modified forms or

varieties, are beneficial as far as prolificness and constitutional vigour

are concerned. On the other hand, changes in the conditions greater in

degree, or of a different nature, and crosses between forms which have been

slowly and greatly modified by natural means,--in other words, between

species,--are highly injurious, as far as the reproductive system is

concerned, and in some few instances as far as constitutional vigour is

concerned. Can this parallelism be accidental? Does it not rather indicate

some real bond of connection? As a fire goes out unless it be stirred up,

so the vital forces are always tending, according to Mr. Herbert Spencer,

to a state of equilibrium, unless disturbed and renovated through the

action of other forces.

In some few cases varieties tend to keep distinct, by breeding at different

periods, by great differences in size, or by sexual preference,--in this

latter respect more especially resembling species in a state of nature. But

the actual crossing of varieties, far from diminishing, generally adds to

the fertility of both the first union and the mongrel offspring. Whether

all {178} the most widely distinct domestic varieties are invariably quite

fertile when crossed, we do not positively know; much time and trouble

would be requisite for the necessary experiments, and many difficulties

occur, such as the descent of the various races from aboriginally distinct

species, and the doubts whether certain forms ought to be ranked as species

or varieties. Nevertheless, the wide experience of practical breeders

proves that the great majority of varieties, even if some should hereafter

prove not to be indefinitely fertile _inter se_, are far more fertile when

crossed, than the vast majority of closely allied natural species. A few

remarkable cases have, however, been given on the authority of excellent

observers, showing that with plants certain forms, which undoubtedly must

be ranked as varieties, yield fewer seeds when crossed than is natural to

the parent-species. Other varieties have had their reproductive powers so

far modified that they are either more or less fertile than are their

parents, when crossed with a distinct species.

Nevertheless, the fact remains indisputable that domesticated varieties of

animals and of plants, which differ greatly from each other in structure,

but which are certainly descended from the same aboriginal species, such as

the races of the fowl, pigeon, many vegetables, and a host of other

productions, are extremely fertile when crossed; and this seems to make a

broad and impassable barrier between domestic varieties and natural

species. But, as I will now attempt to show, the distinction is not so

great and overwhelmingly important as it at first appears.

_On the Difference in Fertility between Varieties and Species when

crossed._

This work is not the proper place for fully treating the subject of

hybridism, and I have already given in my 'Origin of Species' a moderately

full abstract. I will here merely enumerate the general conclusions which

may be relied on, and which bear on our present point.

_Firstly_, the laws governing the production of hybrids are identical, or

nearly identical, in the animal and vegetable kingdoms.

_Secondly_, the sterility of distinct species when first united, {179} and

that of their hybrid offspring, graduates, by an almost infinite number of

steps, from zero, when the ovule is never impregnated and a seed-capsule is

never formed, up to complete fertility. We can only escape the conclusion

that some species are fully fertile when crossed, by determining to

designate as varieties all the forms which are quite fertile. This high

degree of fertility is, however, rare. Nevertheless plants, which have been

exposed to unnatural conditions, sometimes become modified in so peculiar a

manner, that they are much more fertile when crossed by a distinct species

than when fertilised by their own pollen. Success in effecting a first

union between two species, and the fertility of their hybrids, depends in

an eminent degree on the conditions of life being favourable. The innate

sterility of hybrids of the same parentage and raised from the same

seed-capsule often differs much in degree.

_Thirdly_, the degree of sterility of a first cross between two species

does not always run strictly parallel with that of their hybrid offspring.

Many cases are known of species which can be crossed with ease, but yield

hybrids excessively sterile; and conversely some which can be crossed with

great difficulty, but produce fairly fertile hybrids. This is an

inexplicable fact, on the view that species have been specially endowed

with mutual sterility in order to keep them distinct.

_Fourthly_, the degree of sterility often differs greatly in two species

when reciprocally crossed; for the first will readily fertilise the second;

but the latter is incapable, after hundreds of trials, of fertilising the

former. Hybrids produced from reciprocal crosses between the same two

species, likewise sometimes differ in their degree of sterility. These

cases also are utterly inexplicable on the view of sterility being a

special endowment.

_Fifthly_, the degree of sterility of first crosses and of hybrids runs, to

a certain extent, parallel with the general or systematic affinity of the

forms which are united. For species belonging to distinct genera can

rarely, and those belonging to distinct families can never, be crossed. The

parallelism, however, is far from complete; for a multitude of closely

allied species will not unite, or unite with extreme difficulty, whilst

other species, widely different from each other, can be crossed with

perfect facility. Nor does the difficulty depend on ordinary {180}

constitutional differences, for annual and perennial plants, deciduous and

evergreen trees, plants flowering at different seasons, inhabiting

different stations, and naturally living under the most opposite climates,

can often be crossed with ease. The difficulty or facility apparently

depends exclusively on the sexual constitution of the species which are

crossed; or on their sexual elective affinity, _i. e._ _Wahlverwandtschaft_

of Gaertner. As species rarely or never become modified in one character,

without being at the same time modified in many, and as systematic affinity

includes all visible resemblances and dissimilarities, any difference in

sexual constitution between two species would naturally stand in more or

less close relation with their systematic position.

_Sixthly_, the sterility of species when first crossed, and that of

hybrids, may possibly depend to a certain extent on distinct causes. With

pure species the reproductive organs are in a perfect condition, whilst

with hybrids they are often plainly deteriorated. A hybrid embryo which

partakes of the constitution of its father and mother is exposed to

unnatural conditions, as long as it is nourished within the womb, or egg,

or seed of the mother-form; and as we know that unnatural conditions often

induce sterility, the reproductive organs of the hybrid might at this early

age be permanently affected. But this cause has no bearing on the

infertility of first unions. The diminished number of the offspring from

first unions may often result, as is certainly sometimes the case, from the

premature death of most of the hybrid embryos. But we shall immediately see

that a law of an unknown nature apparently exists, which causes the

offspring from unions, which are infertile, to be themselves more or less

infertile; and this at present is all that can be said.

_Seventhly_, hybrids and mongrels present, with the one great exception of

fertility, the most striking accordance in all other respects; namely, in

the laws of their resemblance to their two parents, in their tendency to

reversion, in their variability, and in being absorbed through repeated

crosses by either parent-form.

Since arriving at the foregoing conclusions, condensed from my former work,

I have been led to investigate a subject which throws considerable light on

hybridism, namely, the fertility of {181} reciprocally dimorphic and

trimorphic plants, when illegitimately united. I have had occasion several

times to allude to these plants, and I may here give a brief abstract[441]

of my observations. Several plants belonging to distinct orders present two

forms, which exist in about equal numbers, and which differ in no respect

except in their reproductive organs; one form having a long pistil with

short stamens, the other a short pistil with long stamens; both with

differently sized pollen-grains. With trimorphic plants there are three

forms likewise differing in the lengths of their pistils and stamens, in

the size and colour of the pollen-grains, and in some other respects; and

as in each of the three forms there are two sets of stamens, there are

altogether six sets of stamens and three kinds of pistils. These organs are

so proportioned in length to each other that, in any two of the forms, half

the stamens in each stand on a level with the stigma of the third form. Now

I have shown, and the result has been confirmed by other observers, that,

in order to obtain full fertility with these plants, it is necessary that

the stigma of the one form should be fertilised by pollen taken from the

stamens of corresponding height in the other form. So that with dimorphic

species two unions, which may be called legitimate, are fully fertile, and

two, which may be called illegitimate, are more or less infertile. With

trimorphic species six unions are legitimate or fully fertile, and twelve

are illegitimate or more or less infertile.

The infertility which may be observed in various dimorphic and trimorphic

plants, when they are illegitimately fertilised, that is, by pollen taken

from stamens not corresponding in height with the pistil, differs much in

degree, up to absolute and utter sterility; just in the same manner as

occurs in crossing distinct species. As the degree of sterility in the

latter case depends in an eminent degree on the conditions of life being

more or less favourable, so I have found it with illegitimate unions. It is

well known that if pollen of a distinct species be placed on the stigma of

a flower, and its own pollen be afterwards, even {182} after a considerable

interval of time, placed on the same stigma, its action is so strongly

prepotent that it generally annihilates the effect of the foreign pollen;

so it is with the pollen of the several forms of the same species, for

legitimate pollen is strongly prepotent over illegitimate pollen, when both

are placed on the same stigma. I ascertained this by fertilising several

flowers, first illegitimately, and twenty-four hours afterwards

legitimately, with pollen taken from a peculiarly coloured variety, and all

the seedlings were similarly coloured; this shows that the legitimate

pollen, though applied twenty-four hours subsequently, had wholly destroyed

or prevented the action of the previously applied illegitimate pollen.

Again, as, in making reciprocal crosses between the same two species, there

is occasionally a great difference in the result, so something analogous

occurs with dimorphic plants; for a short-styled cowslip (_P. veris_)

yields more seed when fertilised by the long-styled form, and less seed

when fertilised by its own form, compared with a long-styled cowslip when

fertilised in the two corresponding methods.

In all these respects the forms of the same undoubted species, when

illegitimately united, behave in exactly the same manner as do two distinct

species when crossed. This led me carefully to observe during four years

many seedlings, raised from several illegitimate unions. The chief result

is that these illegitimate plants, as they may be called, are not fully

fertile. It is possible to raise from dimorphic species, both long-styled

and short-styled illegitimate plants, and from trimorphic plants all three

illegitimate forms. These can then be properly united in a legitimate

manner. When this is done, there is no apparent reason why they should not

yield as many seeds as did their parents when legitimately fertilised. But

such is not the case; they are all infertile, but in various degrees; some

being so utterly and incurably sterile that they did not yield during four

seasons a single seed or even seed-capsule. These illegitimate plants,

which are so sterile, although united with each other in a legitimate

manner, may be strictly compared with hybrids when crossed _inter se_, and

it is well known how sterile these latter generally are. When, on the other

hand, a hybrid is crossed with either pure parent-species, the sterility is

usually much lessened: and so it is when an illegitimate plant is

fertilised by {183} a legitimate plant. In the same manner as the sterility

of hybrids does not always run parallel with the difficulty of making the

first cross between the two parent species, so the sterility of certain

illegitimate plants was unusually great, whilst the sterility of the union

from which they were derived was by no means great. With hybrids raised

from the same seed-capsule the degree of sterility is innately variable, so

it is in a marked manner with illegitimate plants. Lastly, many hybrids are

profuse and persistent flowerers, whilst other and more sterile hybrids

produce few flowers, and are weak, miserable dwarfs; exactly similar cases

occur with the illegitimate offspring of various dimorphic and trimorphic

plants.

Altogether there is the closest identity in character and behaviour between

illegitimate plants and hybrids. It is hardly an exaggeration to maintain

that the former are hybrids, but produced within the limits of the same

species by the improper union of certain forms, whilst ordinary hybrids are

produced from an improper union between so-called distinct species. We have

already seen that there is the closest similarity in all respects between

first illegitimate unions, and first crosses between distinct species. This

will perhaps be made more fully apparent by an illustration: we may suppose

that a botanist found two well-marked varieties (and such occur) of the

long-styled form of the trimorphic _Lythrum salicaria_, and that he

determined to try by crossing whether they were specifically distinct. He

would find that they yielded only about one-fifth of the proper number of

seed, and that they behaved in all the other above-specified respects as if

they had been two distinct species. But to make the case sure, he would

raise plants from his supposed hybridised seed, and he would find that the

seedlings were miserably dwarfed and utterly sterile, and that they behaved

in all other respects like ordinary hybrids. He might then maintain that he

had actually proved, in accordance with the common view, that his two

varieties were as good and as distinct species as any in the world; but he

would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are important,

because they show us, firstly, that the physiological {184} test of

lessened fertility, both in first crosses and in hybrids, is no safe

criterion of specific distinction; secondly, because we may conclude that

there must be some unknown law or bond connecting the infertility of

illegitimate unions with that of their illegitimate offspring, and we are

thus led to extend this view to first crosses and hybrids; thirdly, because

we find, and this seems to me of especial importance, that with trimorphic

plants three forms of the same species exist, which when crossed in a

particular manner are infertile, and yet these forms differ in no respect

from each other, except in their reproductive organs,--as in the relative

length of the stamens and pistils, in the size, form, and colour of the

pollen-grains, in the structure of the stigma, and in, the number and size

of the seeds. With these differences and no others, either in organisation

or constitution, we find that the illegitimate unions and the illegitimate

progeny of these three forms are more or less sterile, and closely resemble

in a whole series of relations the first unions and hybrid offspring of

distinct species. From this we may infer that the sterility of species when

crossed and of their hybrid progeny is likewise in all probability

exclusively due to differences confined to the reproductive system. We have

indeed been brought to a similar conclusion by observing that the sterility

of crossed species does not strictly coincide with their systematic

affinity, that is, with the sum of their external resemblances; nor does it

coincide with their similarity in general constitution. But we are more

especially led to this same conclusion by considering reciprocal crosses,

in which the male of one species cannot be united, or can be united with

extreme difficulty, with the female of a second species, whilst the

converse cross can be effected with perfect facility; for this difference

in the facility of making reciprocal crosses, and in the fertility of their

offspring, must be attributed either to the male or female element in the

first species having been differentiated with reference to the sexual

element of the second species in a higher degree than in the converse case.

In so complex a subject as Hybridism it is of considerable importance thus

to arrive at a definitive conclusion, namely, that the sterility which

almost invariably follows the union of distinct {185} species depends

exclusively on differences in their sexual constitution.

* * * * *

On the principle which makes it necessary for man, whilst he is selecting

and improving his domestic varieties, to keep them separate, it would

clearly be advantageous to varieties in a state of nature, that is to

incipient species, if they could be kept from blending, either through

sexual aversion, or by becoming mutually sterile. Hence it at one time

appeared to me probable, as it has to others, that this sterility might

have been acquired through natural selection. On this view we must suppose

that a shade of lessened fertility first spontaneously appeared, like any

other modification, in certain individuals of a species when crossed with

other individuals of the same species; and that successive slight degrees

of infertility, from being advantageous, were slowly accumulated. This

appears all the more probable, if we admit that the structural differences

between the forms of dimorphic and trimorphic plants, as the length and

curvature of the pistil, &c., have been co-adapted through natural

selection; for if this be admitted, we can hardly avoid extending the same

conclusion to their mutual infertility. Sterility moreover has been

acquired through natural selection for other and widely different purposes,

as with neuter insects in reference to their social economy. In the case of

plants, the flowers on the circumference of the truss in the guelder-rose

(_Viburnum opulus_) and those on the summit of the spike in the

feather-hyacinth (_Muscari comosum_) have been rendered conspicuous, and

apparently in consequence sterile, in order that insects might easily

discover and visit the other flowers. But when we endeavour to apply the

principle of natural selection to the acquirement by distinct species of

mutual sterility, we meet with great difficulties. In the first place, it

may be remarked that separate regions are often inhabited by groups of

species or by single species, which when brought together and crossed are

found to be more or less sterile; now it could clearly have been of no

advantage to such separated species to have been rendered mutually sterile,

and consequently this could not have been effected through natural

selection; but it may perhaps be argued, that, if a species were rendered

sterile with {186} some one compatriot, sterility with other species would

follow as a necessary consequence. In the second place, it is as much

opposed to the theory of natural selection, as to the theory of special

creation, that in reciprocal crosses the male element of one form should

have been rendered utterly impotent on a second form, whilst at the same

time the male element of this second form is enabled freely to fertilise

the first form; for this peculiar state of the reproductive system could

not possibly be advantageous to either species.

In considering the probability of natural selection having come into action

in rendering species mutually sterile, one great difficulty will be found

to lie in the existence of many graduated steps from slightly lessened

fertility to absolute sterility. It may be admitted, on the principle above

explained, that it would profit an incipient species if it were rendered in

some slight degree sterile when crossed with its parent-form or with some

other variety; for thus fewer bastardised and deteriorated offspring would

be produced to commingle their blood with the new species in process of

formation. But he who will take the trouble to reflect on the steps by

which this first degree of sterility could be increased through natural

selection to that higher degree which is common to so many species, and

which is universal with species which have been differentiated to a generic

or family rank, will find the subject extraordinarily complex. After mature

reflection it seems to me that this could not have been effected through

natural selection; for it could have been of no direct advantage to an

individual animal to breed badly with another individual of a different

variety, and thus leave few offspring; consequently such individuals could

not have been preserved or selected. Or take the case of two species which

in their present state, when crossed, produce few and sterile offspring;

now, what is there which could favour the survival of those individuals

which happened to be endowed in a slightly higher degree with mutual

infertility and which thus approached by one small step towards absolute

sterility? yet an advance of this kind, if the theory of natural selection

be brought to bear, must have incessantly occurred with many species, for a

multitude are mutually quite barren. With sterile neuter insects we have

reason to {187} believe that modifications in their structure have been

slowly accumulated by natural selection, from an advantage having been thus

indirectly given to the community to which they belonged over other

communities of the same species; but an individual animal, if rendered

slightly sterile when crossed with some other variety, would not thus in

itself gain any advantage, or indirectly give any advantage to its nearest

relatives or to other individuals of the same variety, leading to their

preservation. I infer from these considerations that, as far as animals are

concerned, the various degrees of lessened fertility which occur with

species when crossed cannot have been slowly accumulated by means of

natural selection.

With plants, it is possible that the case may be somewhat different. With

many kinds, insects constantly carry pollen from neighbouring plants to the

stigmas of each flower; and with some species this is effected by the wind.

Now, if the pollen of a variety, when deposited on the stigma of the same

variety, should become by spontaneous variation in ever so slight a degree

prepotent over the pollen of other varieties, this would certainly be an

advantage to the variety; for its own pollen would thus obliterate the

effects of the pollen of other varieties, and prevent deterioration of

character. And the more prepotent the variety's own pollen could be

rendered through natural selection, the greater the advantage would be. We

know from the researches of Gaertner that, with species which are mutually

sterile, the pollen of each is always prepotent on its own stigma over that

of the other species; but we do not know whether this prepotency is a

consequence of the mutual sterility, or the sterility a consequence of the

prepotency. If the latter view be correct, as the prepotency became

stronger through natural selection, from being advantageous to a species in

process of formation, so the sterility consequent on prepotency would at

the same time be augmented; and the final result would be various degrees

of sterility, such as occurs with existing species. This view might be

extended to animals, if the female before each birth received several

males, so that the sexual element of the prepotent male of her own variety

obliterated the effects of the access of previous males belonging to other

varieties; but we have no reason to believe, at least {188} with

terrestrial animals, that this is the ease; as most males and females pair

for each birth, and some few for life.

On the whole we may conclude that with animals the sterility of crossed

species has not been slowly augmented through natural selection; and as

this sterility follows the same general laws in the vegetable as in the

animal kingdom, it is improbable, though apparently possible, that with

plants crossed species should have been rendered sterile by a different

process. From this consideration, and remembering that species which have

never co-existed in the same country, and which therefore could not have

received any advantage from having been rendered mutually infertile, yet

are generally sterile when crossed; and bearing in mind that in reciprocal

crosses between the same two species there is sometimes the widest

difference in their sterility, we must give up the belief that natural

selection has come into play.

As species have not been rendered mutually infertile through the

accumulative action of natural selection, and as we may safely conclude,

from the previous as well as from other and more general considerations,

that they have not been endowed through an act of creation with this

quality, we must infer that it has arisen incidentally during their slow

formation in connection with other and unknown changes in their

organisation. By a quality arising incidentally, I refer to such cases as

different species of animals and plants being differently affected by

poisons to which they are not naturally exposed; and this difference in

susceptibility is clearly incidental on other and unknown differences in

their organisation. So again the capacity in different kinds of trees to be

grafted on each other, or on a third species, differs much, and is of no

advantage to these trees, but is incidental on structural or functional

differences in their woody tissues. We need not feel surprise at sterility

incidentally resulting from crosses between distinct species,--the modified

descendants of a common progenitor,--when we bear in mind how easily the

reproductive system is affected by various causes--often by extremely

slight changes in the conditions of life, by too close interbreeding, and

by other agencies. It is well to bear in mind such cases, as that of the

_Passiflora alata_, which recovered its self-fertility from {189} being

grafted on a distinct species--the cases of plants which normally or

abnormally are self-impotent, but can readily be fertilised by the pollen

of a distinct species--and lastly the cases of individual domesticated

animals which evince towards each other sexual incompatibility.

* * * * *

We now at last come to the immediate point under discussion: how is it

that, with some few exceptions in the case of plants, domesticated

varieties, such as those of the dog, fowl, pigeon, several fruit-trees, and

culinary vegetables, which differ from each other in external characters

more than many species, are perfectly fertile when crossed, or even fertile

in excess, whilst closely allied species are almost invariably in some

degree sterile? We can, to a certain extent, give a satisfactory answer to

this question. Passing over the fact that the amount of external difference

between two species is no sure guide to their degree of mutual sterility,

so that similar differences in the case of varieties would be no sure

guide, we know that with species the cause lies exclusively in differences

in their sexual constitution. Now the conditions to which domesticated

animals and cultivated plants have been subjected, have had so little

tendency towards modifying the reproductive system in a manner leading to

mutual sterility, that we have good grounds for admitting the directly

opposite doctrine of Pallas, namely, that such conditions generally

eliminate this tendency; so that the domesticated descendants of species,

which in their natural state would have been in some degree sterile when

crossed, become perfectly fertile together. With plants, so far is

cultivation from giving a tendency towards mutual sterility, that in

several well-authenticated cases, already often alluded to, certain species

have been affected in a very different manner, for they have become

self-impotent, whilst still retaining the capacity of fertilising, and

being fertilised by, distinct species. If the Pallasian doctrine of the

elimination of sterility through long-continued domestication be admitted,

and it can hardly be rejected, it becomes in the highest degree improbable

that similar circumstances should commonly both induce and eliminate the

same tendency; though in certain cases, with species having a peculiar

constitution, sterility might occasionally be thus {190} induced. Thus, as

I believe, we can understand why with domesticated animals varieties have

not been produced which are mutually sterile; and why with plants only a

few such cases have been observed, namely, by Gaertner, with certain

varieties of maize and verbascum, by other experimentalists with varieties

of the gourd and melon, and by Koelreuter with one kind of tobacco.

With respect to varieties which have originated in a state of nature, it is

almost hopeless to expect to prove by direct evidence that they have been

rendered mutually sterile; for if even a trace of sterility could be

detected, such varieties would at once be raised by almost every naturalist

to the rank of distinct species. If, for instance, Gaertner's statement

were fully confirmed, that the blue and red-flowered forms of the pimpernel

(_Anagallis arvensis_) are sterile when crossed, I presume that all the

botanists who now maintain on various grounds that these two forms are

merely fleeting varieties, would at once admit that they were specifically

distinct.

The real difficulty in our present subject is not, as it appears to me, why

domestic varieties have not become mutually infertile when crossed, but why

this has so generally occurred with natural varieties as soon as they have

been modified in a sufficient and permanent degree to take rank as species.

We are far from precisely knowing the cause; nor is this surprising, seeing

how profoundly ignorant we are in regard to the normal and abnormal action

of the reproductive system. But we can see that species, owing to their

struggle for life with numerous competitors, must have been exposed to more

uniform conditions during long periods of time, than have been domestic

varieties; and this may well make a wide difference in the result. For we

know how commonly wild animals and plants, when taken from their natural

conditions and subjected to captivity, are rendered sterile; and the

reproductive functions of organic beings which have always lived and been

slowly modified under natural conditions would probably in like manner be

eminently sensitive to the influence of an unnatural cross. Domesticated

productions, on the other hand, which, as shown by the mere fact of their

domestication, were not originally highly sensitive to changes in their

conditions of life, and which can now generally resist {191} with

undiminished fertility repeated changes of conditions, might be expected to

produce varieties, which would be little liable to have their reproductive

powers injuriously affected by the act of crossing with other varieties

which had originated in a like manner.

Certain naturalists have recently laid too great stress, as it appears to

me, on the difference in fertility between varieties and species when

crossed. Some allied species of trees cannot be grafted on each other,--all

varieties can be so grafted. Some allied animals are affected in a very

different manner by the same poison, but with varieties no such case until

recently was known, but now it has been proved that immunity from certain

poisons stands in some cases in correlation with the colour of the hair.

The period of gestation generally differs much with distinct species, but

with varieties until lately no such difference had been observed. The time

required for the germination of seeds differs in an analogous manner, and I

am not aware that any difference in this respect has as yet been detected

with varieties. Here we have various physiological differences, and no

doubt others could be added, between one species and another of the same

genus, which do not occur, or occur with extreme rarity, in the case of

varieties; and these differences are apparently wholly or in chief part

incidental on other constitutional differences, just in the same manner as

the sterility of crossed species is incidental on differences confined to

the sexual system. Why, then, should these latter differences, however

serviceable they may indirectly be in keeping the inhabitants of the same

country distinct, be thought of such paramount importance, in comparison

with other incidental and functional differences? No sufficient answer to

this question can be given. Hence the fact that the most distinct domestic

varieties are, with rare exceptions, perfectly fertile when crossed, and

produce fertile offspring, whilst closely allied species are, with rare

exceptions, more or less sterile, is not nearly so formidable an objection

as it appears at first to the theory of the common descent of allied

species.

* * * * *

{192}

CHAPTER XX.

SELECTION BY MAN.

SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL

SELECTION--RESULTS OF METHODICAL SELECTION--CARE TAKEN IN

SELECTION--SELECTION WITH PLANTS--SELECTION CARRIED ON BY THE ANCIENTS,

AND BY SEMI-CIVILIZED PEOPLE--UNIMPORTANT CHARACTERS OFTEN ATTENDED

TO--UNCONSCIOUS SELECTION--AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR

DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS

SELECTION--INFLUENCE OF DIFFERENT BREEDERS ON THE SAME

SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS OF

SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST

VALUED BY MAN.

The power of Selection, whether exercised by man, or brought into play

under nature through the struggle for existence and the consequent survival

of the fittest, absolutely depends on the variability of organic beings.

Without variability nothing can be effected; slight individual differences,

however, suffice for the work, and are probably the sole differences which

are effective in the production of new species. Hence our discussion on the

causes and laws of variability ought in strict order to have preceded our

present subject, as well as the previous subjects of inheritance, crossing,

&c.; but practically the present arrangement has been found the most

convenient. Man does not attempt to cause variability; though he

unintentionally effects this by exposing organisms to new conditions of

life, and by crossing breeds already formed. But variability being granted,

he works wonders. Unless some degree of selection be exercised, the free

commingling of the individuals of the same variety soon obliterates, as we

have previously seen, the slight differences which may arise, and gives to

the whole body of individuals uniformity of character. In separated

districts, long-continued exposure to different conditions of life may

perhaps produce new races without the aid of selection; but to this

difficult subject {193} of the direct action of the conditions of life we

shall in a future chapter recur.

When animals or plants are born with some conspicuous and firmly inherited

new character, selection is reduced to the preservation of such

individuals, and to the subsequent prevention of crosses; so that nothing

more need be said on the subject. But in the great majority of cases a new

character, or some superiority in an old character, is at first faintly

pronounced, and is not strongly inherited; and then the full difficulty of

selection is experienced. Indomitable patience, the finest powers of

discrimination, and sound judgment must be exercised during many years. A

clearly predetermined object must be kept steadily in view. Few men are

endowed with all these qualities, especially with that of discriminating

very slight differences; judgment can be acquired only by long experience;

but if any of these qualities be wanting, the labour of a life may be

thrown away. I have been astonished when celebrated breeders, whose skill

and judgment have been proved by their success at exhibitions, have shown

me their animals, which appeared all alike, and have assigned their reasons

for matching this and that individual. The importance of the great

principle of Selection mainly lies in this power of selecting scarcely

appreciable differences, which nevertheless are found to be transmissible,

and which can be accumulated until the result is made manifest to the eyes

of every beholder.

The principle of selection may be conveniently divided into three kinds.

_Methodical selection_ is that which guides a man who systematically

endeavours to modify a breed according to some predetermined standard.

_Unconscious selection_ is that which follows from men naturally preserving

the most valued and destroying the less valued individuals, without any

thought of altering the breed; and undoubtedly this process slowly works

great changes. Unconscious selection graduates into methodical, and only

extreme cases can be distinctly separated; for he who preserves a useful or

perfect animal will generally breed from it with the hope of getting

offspring of the same character; but as long as he has not a predetermined

purpose to improve the breed, he may be said to be selecting {194}

unconsciously.[442] Lastly, we have _Natural selection_, which implies that

the individuals which are best fitted for the complex, and in the course of

ages changing conditions to which they are exposed, generally survive and

procreate their kind. With domestic productions, with which alone we are

here strictly concerned, natural selection comes to a certain extent into

action, independently of, and even in opposition to, the will of man.

* * * * *

_Methodical Selection._--What man has effected within recent times in

England by methodical selection is clearly shown by our exhibitions of

improved quadrupeds and fancy birds. With respect to cattle, sheep, and

pigs, we owe their great improvement to a long series of well-known

names--Bakewell, Colling, Ellman, Bates, Jonas Webb, Lords Leicester and

Western, Fisher Hobbs, and others. Agricultural writers are unanimous on

the power of selection: any number of statements to this effect could be

quoted; a few will suffice. Youatt, a sagacious and experienced observer,

writes,[443] the principle of selection is "that which enables the

agriculturist, not only to modify the character of his flock, but to change

it altogether." A great breeder of shorthorns[444] says, "In the anatomy of

the shoulder modern breeders have made great improvements on the Ketton

shorthorns by correcting the defect in the knuckle or shoulder-joint, and

by laying the top of the shoulder more snugly into the crop, and thereby

filling up the hollow behind it.... The eye has its fashion at different

periods: at one time the eye high and outstanding from the head, and at

another time the sleepy eye sunk into the head; but these extremes have

merged into the medium of a full, clear, and prominent eye with a placid

look."

Again, hear what an excellent judge of pigs[445] says: "The legs {195}

should be no longer than just to prevent the animal's belly from trailing

on the ground. The leg is the least profitable portion of the hog, and we

therefore require no more of it than is absolutely necessary for the

support of the rest." Let any one compare the wild-boar with any improved

breed, and he will see how effectually the legs have been shortened.

Few persons, except breeders, are aware of the systematic care taken in

selecting animals, and of the necessity of having a clear and almost

prophetic vision into futurity. Lord Spencer's skill and judgment were well

known; and he writes,[446] "It is therefore very desirable, before any man

commences to breed either cattle or sheep, that he should make up his mind

to the shape and qualities he wishes to obtain, and steadily pursue this

object." Lord Somerville, in speaking of the marvellous improvement of the

New Leicester sheep, effected by Bakewell and his successors, says, "It

would seem as if they had first drawn a perfect form, and then given it

life." Youatt[447] urges the necessity of annually drafting each flock, as

many animals will certainly degenerate "from the standard of excellence,

which the breeder has established in his own mind." Even with a bird of

such little importance as the canary, long ago (1780-1790) rules were

established, and a standard of perfection was fixed, according to which the

London fanciers tried to breed the several sub-varieties.[448] A great

winner of prizes at the Pigeon-shows,[449] in describing the Short-faced

Almond Tumbler, says, "There are many first-rate fanciers who are

particularly partial to what is called the goldfinch-beak, which is very

beautiful; others say, take a full-size round cherry, then take a

barley-corn, and judiciously placing and thrusting it into the cherry, form

as it were your beak; and that is not all, for it will form a good head and

beak, provided, as I said before, it is judiciously done; others take an

oat; but as I think the goldfinch-beak the handsomest, I would advise the

inexperienced fancier to get the head of a goldfinch, and keep it by him

for his observation." Wonderfully different as is the beak of the

rock-pigeon and goldfinch, undoubtedly, as far as {196} external shape and

proportions are concerned, the end has been nearly gained.

Not only should our animals be examined with the greatest care whilst

alive, but, as Anderson remarks,[450] their carcases should be scrutinised,

"so as to breed from the descendants of such only as, in the language of

the butcher, cut up well." The "grain of the meat" in cattle, and its being

well marbled with fat,[451] and the greater or less accumulation of fat in

the abdomen of our sheep, have been attended to with success. So with

poultry, a writer,[452] speaking of Cochin-China fowls, which are said to

differ much in the quality of their flesh, says, "the best mode is to

purchase two young brother-cocks, kill, dress, and serve up one; if he be

indifferent, similarly dispose of the other, and try again; if, however, he

be fine and well-flavoured, his brother will not be amiss for breeding

purposes for the table."

The great principle of the division of labour has been brought to bear on

selection. In certain districts[453] "the breeding of bulls is confined to

a very limited number of persons, who by devoting their whole attention to

this department, are able from year to year to furnish a class of bulls

which are steadily improving the general breed of the district." The

rearing and letting of choice rams has long been, as is well known, a chief

source of profit to several eminent breeders. In parts of Germany this

principle is carried with merino sheep to an extreme point.[454] "So

important is the proper selection of breeding animals considered, that the

best flock-masters do not trust to their own judgment, or to that of their

shepherds, but employ persons called 'sheep-classifiers,' who make it their

special business to attend to this part of the management of several

flocks, and thus to preserve, or if possible to improve, the best qualities

of both parents in the lambs." In Saxony, "when the lambs are weaned, each

in his turn is placed upon a table that his wool and form may be minutely

observed. {197} The finest are selected for breeding and receive a first

mark. When they are one year old, and prior to shearing them, another close

examination of those previously marked takes place: those in which no

defect can be found receive a second mark, and the rest are condemned. A

few months afterwards a third and last scrutiny is made; the prime rams and

ewes receive a third and final mark, but the slightest blemish is

sufficient to cause the rejection of the animal." These sheep are bred and

valued almost exclusively for the fineness of their wool; and the result

corresponds with the labour bestowed on their selection. Instruments have

been invented to measure accurately the thickness of the fibres; and "an

Austrian fleece has been produced of which twelve hairs equalled in

thickness one from a Leicester sheep."

Throughout the world, wherever silk is produced, the greatest care is

bestowed on selecting the cocoons from which the moths for breeding are to

be reared. A careful cultivator[455] likewise examines the moths

themselves, and destroys those that are not perfect. But what more

immediately concerns us is that certain families in France devote

themselves to raising eggs for sale.[456] In China, near Shanghai, the

inhabitants of two small districts have the privilege of raising eggs for

the whole surrounding country, and that they may give up their whole time

to this business, they are interdicted by law from producing silk.[457]

The care which successful breeders take in matching their birds is

surprising. Sir John Sebright, whose fame is perpetuated by the "Sebright

Bantam," used to spend "two and three days in examining, consulting, and

disputing with a friend which were the best of five or six birds."[458] Mr.

Bult, whose pouter-pigeons won so many prizes and were exported to North

America under the charge of a man sent on purpose, told me that he always

deliberated for several days before he matched each pair. Hence we can

understand the advice of an eminent fancier, who writes,[459] "I would here

particularly guard {198} you against having too great a variety of pigeons,

otherwise you will know a little of all, but nothing about one as it ought

to be known." Apparently it transcends the power of the human intellect to

breed all kinds: "it is possible that there may be a few fanciers that have

a good general knowledge of fancy pigeons; but there are many more who

labour under the delusion of supposing they know what they do not." The

excellence of one sub-variety, the Almond Tumbler, lies in the plumage,

carriage, head, beak, and eye; but it is too presumptuous in the beginner

to try for all these points. The great judge above quoted says, "there are

some young fanciers who are over-covetous, who go for all the above five

properties at once; they have their reward by getting nothing." We thus see

that breeding even fancy pigeons is no simple art: we may smile at the

solemnity of these precepts, but he who laughs will win no prizes.

What methodical selection has effected for our animals is sufficiently

proved, as already remarked, by our Exhibitions. So greatly were the sheep

belonging to some of the earlier breeders, such as Bakewell and Lord

Western, changed, that many persons could not be persuaded that they had

not been crossed. Our pigs, as Mr. Corringham remarks,[460] during the last

twenty years have undergone, through rigorous selection together with

crossing, a complete metamorphosis. The first exhibition for poultry was

held in the Zoological Gardens in 1845; and the improvement effected since

that time has been great. As Mr. Baily, the great judge, remarked to me, it

was formerly ordered that the comb of the Spanish cock should be upright,

and in four or five years all good birds had upright combs; it was ordered

that the Polish cock should have no comb or wattles, and now a bird thus

furnished would be at once disqualified; beards were ordered, and out of

fifty-seven pens lately (1860) exhibited at the Crystal Palace, all had

beards. So it has been in many other cases. But in all cases the judges

order only what is occasionally produced and what can be improved and

rendered constant by selection. The steady increase of weight during the

last few years in our {199} fowls, turkeys, ducks, and geese is notorious;

"six-pound ducks are now common, whereas four pounds was formerly the

average." As the actual time required to make a change has not often been

recorded, it may be worth mentioning that it took Mr. Wicking thirteen

years to put a clean white head on an almond tumbler's body, "a triumph,"

says another fancier, "of which he may be justly proud."[461]

Mr. Tollet, of Betley Hall, selected cows, and especially bulls, descended

from good milkers, for the sole purpose of improving his cattle for the

production of cheese; he steadily tested the milk with the lactometer, and

in eight years he increased, as I was informed by him, the product in the

proportion of four to three. Here is a curious case[462] of steady but slow

progress, with the end not as yet fully attained: in 1784 a race of

silkworms was introduced into France, in which one hundred out of the

thousand failed to produce white cocoons; but now, after careful selection

during sixty-five generations, the proportion of yellow cocoons has been

reduced to thirty-five in the thousand.

With plants selection has been followed with the same good results as with

animals. But the process is simpler, for plants in the great majority of

cases bear both sexes. Nevertheless, with most kinds it is necessary to

take as much care to prevent crosses as with animals or unisexual plants;

but with some plants, such as peas, this care does not seem to be

necessary. With all improved plants, excepting of course those which are

propagated by buds, cuttings, &c., it is almost indispensable to examine

the seedlings and destroy those which depart from the proper type. This is

called "roguing," and is, in fact, a form of selection, like the rejection

of inferior animals. Experienced horticulturists and agriculturists

incessantly urge every one to preserve the finest plants for the production

of seed.

Although plants often present much more conspicuous variations than

animals, yet the closest attention is generally requisite to detect each

slight and favourable change. Mr. Masters relates[463] how "many a patient

hour was devoted," whilst he was {200} young, to the detection of

differences in peas intended for seed. Mr. Barnet[464] remarks that the old

scarlet American strawberry was cultivated for more than a century without

producing a single variety; and another writer observes how singular it was

that when gardeners first began to attend to this fruit it began to vary;

the truth no doubt being that it had always varied, but that, until slight

varieties were selected and propagated by seed, no conspicuous result was

obtained. The finest shades of difference in wheat have been discriminated

and selected with almost as much care, as we see in Colonel Le Couteur's

works, as in the case of the higher animals; but with our cereals the

process of selection has seldom or never been long continued.

It may be worth while to give a few examples of methodical selection with

plants; but in fact the great improvement of all our anciently cultivated

plants may be attributed to selection long carried on, in part

methodically, and in part unconsciously. I have shown in a former chapter

how the weight of the gooseberry has been increased by systematic selection

and culture. The flowers of the Heartsease have been similarly increased in

size and regularity of outline. With the Cineraria, Mr. Glenny[465] "was

bold enough, when the flowers were ragged and starry and ill defined in

colour, to fix a standard which was then considered outrageously high and

impossible, and which, even if reached, it was said, we should be no

gainers by, as it would spoil the beauty of the flowers. He maintained that

he was right; and the event has proved it to be so." The doubling of

flowers has several times been effected by careful selection: the Rev. W.

Williamson,[466] after sowing during several years seed of _Anemone

coronaria_, found a plant with one additional petal; he sowed the seed of

this, and by perseverance in the same course obtained several varieties

with six or seven rows of petals. The single Scotch rose was doubled, and

yielded eight good varieties in nine or ten years.[467] The Canterbury bell

(_Campanula medium_) was doubled by careful selection in four

generations.[468] In four years Mr. Buckman,[469] by culture and {201}

careful selection, converted parsnips, raised from wild seed, into a new

and good variety. By selection during a long course of years, the early

maturity of peas has been hastened from ten to twenty-one days.[470] A more

curious case is offered by the beet-plant, which, since its cultivation in

France, has almost exactly doubled its yield of sugar. This has been

effected by the most careful selection; the specific gravity of the roots

being regularly tested, and the best roots saved for the production of

seed.[471]

_Selection by Ancient and Semi-civilised People._

In attributing so much importance to the selection of animals and plants,

it may be objected that methodical selection would not have been carried on

during ancient times. A distinguished naturalist considers it as absurd to

suppose that semi-civilised people should have practised selection of any

kind. Undoubtedly the principle has been systematically acknowledged and

followed to a far greater extent within the last hundred years than at any

former period, and a corresponding result has been gained; but it would be

a great error to suppose, as we shall immediately see, that its importance

was not recognised and acted on during the most ancient times, and by

semi-civilised people. I should premise that many facts now to be given

only show that care was taken in breeding; but when this is the case,

selection is almost sure to be practised to a certain extent. We shall

hereafter be enabled better to judge how far selection, when only

occasionally carried on, by a few of the inhabitants of a country, will

slowly produce a great effect.

In a well-known passage in the thirtieth chapter of Genesis, rules are

given for influencing, as was then thought possible, the colour of sheep;

and speckled and dark breeds are spoken of as being kept separate. By the

time of David the fleece was likened to snow. Youatt,[472] who has

discussed all the passages in relation to breeding in the Old Testament,

concludes that {202} at this early period "some of the best principles of

breeding must have been steadily and long pursued." It was ordered,

according to Moses, that "Thou shalt not let thy cattle gender with a

diverse kind;" but mules were purchased,[473] so that at this early period

other nations must have crossed the horse and ass. It is said[474] that

Erichthonius, some generations before the Trojan war, had many brood-mares,

"which by his care and judgment in the choice of stallions produced a breed

of horses superior to any in the surrounding countries." Homer (Book v.)

speaks of Aeneas's horses as bred from mares which were put to the steeds

of Laomedon. Plato, in his 'Republic,' says to Glaucus, "I see that you

raise at your house a great many dogs for the chase. Do you take care about

breeding and pairing them? Among animals of good blood, are there not

always some which are superior to the rest?" To which Glaucus answers in

the affirmative.[475] Alexander the Great selected the finest Indian cattle

to send to Macedonia to improve the breed.[476] According to Pliny,[477]

King Pyrrhus had an especially valuable breed of oxen; and he did not

suffer the bulls and cows to come together till four years old, that the

breed might not degenerate. Virgil, in his Georgics (lib. iii.), gives as

strong advice as any modern agriculturist could do, carefully to select the

breeding stock; "to note the tribe, the lineage, and the sire; whom to

reserve for husband of the herd;"--to brand the progeny;--to select sheep

of the purest white, and to examine if their tongues are swarthy. We have

seen that the Romans kept pedigrees of their pigeons, and this would have

been a senseless proceeding had not great care been taken in breeding them.

Columella gives detailed instructions about breeding fowls: "Let the

breeding hens therefore be of a choice colour, a robust body, square-built,

full-breasted, with large heads, with upright and bright-red combs. Those

are believed to be the best bred which have five toes."[478] According to

Tacitus, the Celts attended to the races of their domestic animals; {203}

and Caesar states that they paid high prices to merchants for fine imported

horses.[479] In regard to plants, Virgil speaks of yearly culling the

largest seeds; and Celsus says, "where the corn and crop is but small, we

must pick out the best ears of corn, and of them lay up our seed separately

by itself."[480]

Coming down the stream of time, we may be brief. At about the beginning of

the ninth century Charlemagne expressly ordered his officers to take great

care of his stallions; and if any proved bad or old, to forewarn him in

good time before they were put to the mares.[481] Even in a country so

little civilised as Ireland during the ninth century, it would appear from

some ancient verses,[482] describing a ransom demanded by Cormac, that

animals from particular places, or having a particular character, were

valued. Thus it is said,--

Two pigs of the pigs of Mac Lir,

A ram and ewe both round and red,

I brought with me from Aengus.

I brought with me a stallion and a mare

From the beautiful stud of Manannan,

A bull and a white cow from Druim Cain.

Athelstan, in 930, received as a present from Germany, running-horses; and

he prohibited the exportation of English horses. King John imported "one

hundred chosen stallions from Flanders."[483] On June 16th, 1305, the

Prince of Wales wrote to the Archbishop of Canterbury, begging for the loan

of any choice stallion, and promising its return at the end of the

season.[484] There are numerous records at ancient periods in English

history of the importation of choice animals of various kinds, and of

foolish laws against their exportation. In the reigns of Henry VII. and

VIII. it was ordered that the magistrates, at Michaelmas, should scour the

heaths and commons, and destroy all mares beneath a certain size.[485] Some

of our earlier kings passed laws against the slaughtering rams of any good

breed before they were seven years old, so that they {204} might have time

to breed. In Spain Cardinal Ximenes issued, in 1509, regulations on the

_selection_ of good rams for breeding.[486]

The Emperor Akbar Khan before the year 1600 is said to have "wonderfully

improved" his pigeons by crossing the breeds; and this necessarily implies

careful selection. About the same period the Dutch attended with the

greatest care to the breeding of these birds. Belon in 1555 says that good

managers in France examined the colour of their goslings in order to get

geese of a white colour and better kinds. Markham in 1631 tells the breeder

"to elect the largest and goodliest conies," and enters into minute

details. Even with respect to seeds of plants for the flower-garden, Sir J.

Hanmer writing about the year 1660[487] says, in "choosing seed, the best

seed is the most weighty, and is had from the lustiest and most vigorous

stems;" and he then gives rules about leaving only a few flowers on plants

for seed; so that even such details were attended to in our flower-gardens

two hundred years ago. In order to show that selection has been silently

carried on in places where it would not have been expected, I may add that

in the middle of the last century, in a remote part of North America, Mr.

Cooper improved by careful selection all his vegetables, "so that they were

greatly superior to those of any other person. When his radishes, for

instance, are fit for use, he takes ten or twelve that he most approves,

and plants them at least 100 yards from others that blossom at the same

time. In the same manner he treats all his other plants, varying the

circumstances according to their nature."[488]

In the great work on China published in the last century by the Jesuits,

and which is chiefly compiled from ancient Chinese encyclopaedias, it is

said that with sheep "improving the breed consists in choosing with

particular care the lambs which are destined for propagation, in nourishing

them well, and in keeping the flocks separate." The same principles were

applied by the Chinese to various plants and fruit-trees.[489] An {205}

imperial edict recommends the choice of seed of remarkable size; and

selection was practised even by imperial hands, for it is said that the

Ya-mi, or imperial rice, was noticed at an ancient period in a field by the

Emperor Khang-hi, was saved and cultivated in his garden, and has since

become valuable from being the only kind which will grow north of the Great

Wall.[490] Even with flowers, the tree paeony (_P. moutan_) has been

cultivated, according to Chinese traditions, for 1400 years; between 200

and 300 varieties have been raised, which are cherished like tulips

formerly were by the Dutch.[491]

Turning now to semi-civilised people and to savages: it occurred to me,

from what I had seen of several parts of South America, where fences do not

exist, and where the animals are of little value, that there would be

absolutely no care in breeding or selecting them; and this to a large

extent is true. Roulin,[492] however, describes in Colombia a naked race of

cattle, which are not allowed to increase, on account of their delicate

constitution. According to Azara[493] horses are often born in Paraguay

with curly hair; but, as the natives do not like them, they are destroyed.

On the other hand, Azara states that a hornless bull, born in 1770, was

preserved and propagated its race. I was informed of the existence in Banda

Oriental of a breed with reversed hair; and the extraordinary niata cattle

first appeared and have since been kept distinct in La Plata. Hence certain

conspicuous variations have been preserved, and others have been habitually

destroyed, in these countries, which are so little favourable for careful

selection. We have also seen that the inhabitants sometimes introduce

cattle on their estates to prevent the evil effects of close interbreeding.

On the other hand, I have heard on reliable authority that the Gauchos of

the Pampas never take any pains in selecting the best bulls or stallions

for breeding; and this probably accounts for the cattle and horses being

remarkably uniform in character throughout the immense range of the

Argentine republic.

Looking to the Old World, in the Sahara Desert "The Touareg is as careful

in the selection of his breeding Mahari {206} (a fine race of the

dromedary) as the Arab is in that of his horse. The pedigrees are handed

down, and many a dromedary can boast a genealogy far longer than the

descendants of the Darley Arabian."[494] According to Pallas the Mongolians

endeavour to breed the Yaks or horse-tailed buffaloes with white tails, for

these are sold to the Chinese mandarins as fly-flappers; and Moorcroft,

about seventy years after Pallas, found that white-tailed animals were

still selected for breeding.[495]

We have seen in the chapter on the Dog that savages in different parts of

North America and in Guiana cross their dogs with wild Canidae, as did the

ancient Gauls, according to Pliny. This was done to give their dogs

strength and vigour, in the same way as the keepers in large warrens now

sometimes cross their ferrets (as I have been informed by Mr. Yarrell) with

the wild polecat, "to give them more devil." According to Varro, the wild

ass was formerly caught and crossed with the tame animal to improve the

breed, in the same manner as at the present day the natives of Java

sometimes drive their cattle into the forests to cross with the wild

Banteng (_Bos sondaicus_).[496] In Northern Siberia, among the Ostyaks the

dogs vary in markings in different districts, but in each place they are

spotted black and white in a remarkably uniform manner;[497] and from this

fact alone we may infer careful breeding, more especially as the dogs of

one locality are famed throughout the country for their superiority. I have

heard of certain tribes of Esquimaux who take pride in their teams of dogs

being uniformly coloured. In Guiana, as Sir R. Schomburgk informs me,[498]

the dogs of the Turuma Indians are highly valued and extensively bartered:

the price of a good one is the same as that given for a wife: they are kept

in a sort of cage, and the Indians "take great care when the female is in

season to prevent her uniting with a dog of an inferior description." The

Indians told Sir Robert that, if a dog proved bad or useless, {207} he was

not killed, but was left to die from sheer neglect. Hardly any nation is

more barbarous than the Fuegians, but I hear from Mr. Bridges, the

Catechist to the Mission, that, "when these savages have a large, strong,

and active bitch, they take care to put her to a fine dog, and even take

care to feed her well, that her young may be strong and well favoured."

In the interior of Africa, negroes, who have not associated with white men,

show great anxiety to improve their animals: they "always choose the larger

and stronger males for stock:" the Malakolo were much pleased at

Livingstone's promise to send them a bull, and some Bakalolo carried a live

cock all the way from Loanda into the interior.[499] Further south on the

same continent, Andersson states that he has known a Damara give two fine

oxen for a dog which struck his fancy. The Damaras take great delight in

having whole droves of cattle of the same colour, and they prize their oxen

in proportion to the size of their horns. "The Namaquas have a perfect

mania for a uniform team; and almost all the people of Southern Africa

value their cattle next to their women, and take a pride in possessing

animals that look high-bred." "They rarely or never make use of a handsome

animal as a beast of burden."[500] The power of discrimination which these

savages possess is wonderful, and they can recognise to which tribe any

cattle belong. Mr. Andersson further informs me that the natives frequently

match a particular bull with a particular cow.

The most curious case of selection by semi-civilised people, or indeed by

any people, which I have found recorded, is that given by Garcilazo de la

Vega, a descendant of the Incas, as having been practised in Peru before

the country was subjugated by the Spaniards.[501] The Incas annually held

great hunts, when all the wild animals were driven from an immense circuit

to a central point. The beasts of prey were first destroyed as injurious.

The wild Guanacos and Vicunas were sheared; the old males and females

killed, and the others set at liberty. The various kinds of deer were

examined; the old males and females {208} were likewise killed; "but the

young females, with a certain number of males, selected from the most

beautiful and strong," were given their freedom. Here, then, we have

selection by man aiding natural selection. So that the Incas followed

exactly the reverse system of that which our Scottish sportsmen are accused

of following, namely, of steadily killing the finest stags, thus causing

the whole race to degenerate.[502] In regard to the domesticated llamas and

alpacas, they were separated in the time of the Incas according to colour;

and if by chance one in a flock was born of the wrong colour, it was

eventually put into another flock.

In the genus Auchenia there are four forms,--the Guanaco and Vicuna, found

wild and undoubtedly distinct species; the Llama and Alpaca, known only in

a domesticated condition. These four animals appear so different, that most

professed naturalists, especially those who have studied these animals in

their native country, maintain that they are specifically distinct,

notwithstanding that no one pretends to have seen a wild llama or alpaca.

Mr. Ledger, however, who has closely studied these animals both in Peru and

during their exportation to Australia, and who has made many experiments on

their propagation, adduces arguments[503] which seem to me conclusive, that

the llama is the domesticated descendant of the guanaco, and the alpaca of

the vicuna. And now that we know that these animals many centuries ago were

systematically bred and selected, there is nothing surprising in the great

amount of change which they have undergone.

It appeared to me at one time probable that, though ancient and

semi-civilised people might have attended to the improvement of their more

useful animals in essential points, yet that they would have disregarded

unimportant characters. But human nature is the same throughout the world:

fashion everywhere reigns supreme, and man is apt to value whatever he may

chance to possess. We have seen that in South America the niata cattle,

which certainly are not made useful by their shortened faces and upturned

nostrils, have been preserved. The Damaras of South Africa value their

cattle for uniformity {209} of colour and enormously long horns. The

Mongolians value their yaks for their white tails. And I shall now show

that there is hardly any peculiarity in our most useful animals which, from

fashion, superstition, or some other motive, has not been valued, and

consequently preserved. With respect to cattle, "an early record,"

according to Youatt,[504] "speaks of a hundred white cows with red ears

being demanded as a compensation by the princes of North and South Wales.

If the cattle were of a dark or black colour, 150 were to be presented." So

that colour was attended to in Wales before its subjugation by England. In

Central Africa, an ox that beats the ground with its tail is killed; and in

South Africa some of the Damaras will not eat the flesh of a spotted ox.

The Kaffirs value an animal with a musical voice; and "at a sale in British

Kaffraria the low of a heifer excited so much admiration that a sharp

competition sprung up for her possession, and she realised a considerable

price."[505] With respect to sheep, the Chinese prefer rams without horns;

the Tartars prefer them with spirally wound horns, because the hornless are

thought to lose courage.[506] Some of the Damaras will not eat the flesh of

hornless sheep. In regard to horses, at the end of the fifteenth century

animals of the colour described as _liart pomme_ were most valued in

France. The Arabs have a proverb, "Never buy a horse with four white feet,

for he carries his shroud with him;"[507] the Arabs also, as we have seen,

despise dun-coloured horses. So with dogs, Xenophon and others at an

ancient period were prejudiced in favour of certain colours; and "white or

slate-coloured hunting dogs were not esteemed."[508]

Turning to poultry, the old Roman gourmands thought that the liver of a

white goose was the most savoury. In Paraguay black-skinned fowls are kept

because they are thought to be more productive, and their flesh the most

proper for invalids.[509] In Guiana, as I am informed by Sir R. Schomburgk,

the aborigines will not eat the flesh or eggs of the fowl, but two {210}

races are kept distinct merely for ornament. In the Philippines, no less

than nine sub-varieties of the game cock are kept and named, so that they

must be separately bred.

At the present time in Europe, the smallest peculiarities are carefully

attended to in our most useful animals, either from fashion, or as a mark

of purity of blood. Many examples could be given, two will suffice. "In the

Western counties of England the prejudice against a white pig is nearly as

strong as against a black one in Yorkshire." In one of the Berkshire

sub-breeds, it is said, "the white should be confined to four white feet, a

white spot between the eyes, and a few white hairs behind each shoulder."

Mr. Saddler possessed "three hundred pigs, every one of which was marked in

this manner."[510] Marshall, towards the close of the last century, in

speaking of a change in one of the Yorkshire breeds of cattle, says the

horns have been considerably modified, as "a clean, small, sharp horn has

been _fashionable_ for the last twenty years."[511] In a part of Germany

the cattle of the Race de Gfoehl are valued for many good qualities, but

they must have horns of a particular curvature and tint, so much so that

mechanical means are applied if they take a wrong direction; but the

inhabitants "consider it of the highest importance that the nostrils of the

bull should be flesh-coloured, and the eyelashes light; this is an

indispensable condition. A calf with blue nostrils would not be purchased,

or purchased at a very low price."[512] Therefore let no man say that any

point or character is too trifling to be methodically attended to and

selected by breeders.

* * * * *

_Unconscious Selection._--By this term I mean, as already more than once

explained, the preservation by man of the most valued, and the destruction

of the least valued individuals, without any conscious intention on his

part of altering the breed. It is difficult to offer direct proofs of the

results which follow from this kind of selection; but the indirect evidence

is abundant. In fact, except that in the one case man acts intentionally,

and in the other unintentionally, there is little difference between {211}

methodical and unconscious selection. In both cases man preserves the

animals which are most useful or pleasing to him, and destroys or neglects

the others. But no doubt a far more rapid result follows from methodical

than from unconscious selection. The "roguing" of plants by gardeners, and

the destruction by law in Henry VIII.'s reign of all under-sized mares, are

instances of a process the reverse of selection in the ordinary sense of

the word, but leading to the same general result. The influence of the

destruction of individuals having a particular character is well shown by

the necessity of killing every lamb with a trace of black about it, in

order to keep the flock white; or again, by the effects on the average

height of the men of France of the destructive wars of Napoleon, by which

many tall men were killed, the short ones being left to be the fathers of

families. This at least is the conclusion of those who have closely studied

the subject of the conscription; and it is certain that since Napoleon's

time the standard for the army has been lowered two or three times.

Unconscious selection so blends into methodical that it is scarcely

possible to separate them. When a fancier long ago first happened to notice

a pigeon with an unusually short beak, or one with the tail-feathers

unusually developed, although he bred from these birds with the distinct

intention of propagating the variety, yet he could not have intended to

make a short-faced tumbler or a fantail, and was far from knowing that he

had made the first step towards this end. If he could have seen the final

result, he would have been struck with astonishment, but, from what we know

of the habits of fanciers, probably not with admiration. Our English

carriers, barbs, and short-faced tumblers have been greatly modified in the

same manner, as we may infer both from the historical evidence given in the

chapters on the Pigeon, and from the comparison of birds brought from

distant countries.

So it has been with dogs; our present fox-hounds differ from the old

English hound; our greyhounds have become lighter; the wolf-dog, which

belonged to the greyhound class, has become extinct; the Scotch deer-hound

has been modified, and is now rare. Our bulldogs differ from those which

were formerly used for baiting bulls. Our pointers and Newfoundlands do not

{212} closely resemble any native dog now found in the countries whence

they were brought, These changes have been effected partly by crosses; but

in every case the result has been governed by the strictest selection.

Nevertheless there is no reason to suppose that man intentionally and

methodically made the breeds exactly what they now are. As our horses

became fleeter, and the country more cultivated and smoother, fleeter

fox-hounds were desired and produced, but probably without any one

distinctly foreseeing what they would become. Our pointers and setters, the

latter almost certainly descended from large spaniels, have been greatly

modified in accordance with fashion and the desire for increased speed.

Wolves have become extinct, deer have become rarer, bulls are no longer

baited, and the corresponding breeds of the dog have answered to the

change. But we may feel almost sure that when, for instance, bulls were no

longer baited, no man said to himself, I will now breed my dogs of smaller

size, and thus create the present race. As circumstances changed, men

unconsciously and slowly modified their course of selection.

With race-horses selection for swiftness has been followed methodically,

and our horses can now easily beat their progenitors. The increased size

and different appearance of the English race-horse led a good observer in

India to ask, "Could any one in this year of 1856, looking at our

race-horses, conceive that they were the result of the union of the Arab

horse and the African mare?"[513] This change has, it is probable, been

largely effected through unconscious selection, that is, by the general

wish to breed as fine horses as possible in each generation, combined with

training and high feeding, but without any intention to give to them their

present appearance. According to Youatt,[514] the introduction in Oliver

Cromwell's time of three celebrated Eastern stallions speedily affected the

English breed; "so that Lord Harleigh, one of the old school, complained

that the great horse was fast disappearing." This is an excellent proof how

carefully selection must have been attended to; for without such care, all

traces of so small an infusion of Eastern blood would soon have been

absorbed and {213} lost. Notwithstanding that the climate of England has

never been esteemed particularly favourable to the horse, yet

long-continued selection, both methodical and unconscious, together with

that practised by the Arabs during a still longer and earlier period, has

ended in giving us the best breed of horses in the world. Macaulay[515]

remarks, "Two men whose authority on such subjects was held in great

esteem, the Duke of Newcastle and Sir John Fenwick, pronounced that the

meanest hack ever imported from Tangier would produce a finer progeny than

could be expected from the best sire of our native breed. They would not

readily have believed that a time would come when the princes and nobles of

neighbouring lands would be as eager to obtain horses from England as ever

the English had been to obtain horses from Barbary."

The London dray-horse, which differs so much in appearance from any natural

species, and which from its size has so astonished many Eastern princes,

was probably formed by the heaviest and most powerful animals having been

selected during many generations in Flanders and England, but without the

least intention or expectation of creating a horse such as we now see. If

we go back to an early period of history, we behold in the antique Greek

statues, as Schaaffhausen has remarked,[516] a horse equally unlike a race

or dray horse, and differing from any existing breed.

The results of unconscious selection, in an early stage, are well shown in

the difference between the flocks descended from the same stock, but

separately reared by careful breeders. Youatt gives an excellent instance

of this fact in the sheep belonging to Messrs. Buckley and Burgess, which

"have been purely bred from the original stock of Mr. Bakewell for upwards

of fifty years. There is not a suspicion existing in the mind of any one at

all acquainted with the subject that the owner of either flock has deviated

in any one instance from the pure blood of Mr. Bakewell's flock; yet the

difference between the sheep possessed by these two gentlemen is so great,

that they have the appearance of being quite different varieties."[517] I

have seen several analogous and {214} well-marked cases with pigeons: for

instance, I had a family of barbs, descended from those long bred by Sir J.

Sebright, and another family long bred by another fancier, and the two

families plainly differed from each other. Nathusius--and a more competent

witness could not be cited--observes that, though the Shorthorns are

remarkably uniform inn appearance (except in colouring), yet that the

individual character and wishes of each breeder become impressed on his

cattle, so that different herds differ slightly from each other.[518] The

Hereford cattle assumed their present well-marked character soon after the

year 1769, through careful selection by Mr. Tomkins,[519] and the breed has

lately split into two strains--one strain having a white face, and

differing slightly, it is said,[520] in some other points; but there is no

reason to believe that this split, the origin of which is unknown, was

intentionally made; it may with much more probability be attributed to

different breeders having attended to different points. So again, the

Berkshire breed of swine in the year 1810 had greatly changed from what it

had been in 1780; and since 1810 at least two distinct sub-breeds have

borne this same name.[521] When we bear in mind how rapidly all animals

increase, and that some must be annually slaughtered and some saved for

breeding, then, if the same breeder during a long course of years

deliberately settles which shall be saved and which shall be killed, it is

almost inevitable that his individual frame of mind will influence the

character of his stock, without his having had any intention to modify the

breed or form a new strain.

Unconscious selection in the strictest sense of the word, that is, the

saving of the more useful animals and the neglect or slaughter of the less

useful, without any thought of the future, must have gone on occasionally

from the remotest period and amongst the most barbarous nations. Savages

often suffer from famines, and are sometimes expelled by war from their own

homes. In such cases it can hardly be doubted that they would save their

most useful animals. When the Fuegians {215} are hard pressed by want, they

kill their old women for food rather than their dogs; for, as we were

assured, "old women no use--dogs catch otters." The same sound sense would

surely lead them to preserve their more useful dogs when still harder

pressed by famine. Mr. Oldfield, who has seen so much of the aborigines of

Australia, informs me that "they are all very glad to get a European

kangaroo dog, and several instances have been known of the father killing

his own infant that the mother might suckle the much-prized puppy."

Different kinds of dogs would be useful to the Australian for hunting

opossums and kangaroos, and to the Fuegian for catching fish and otters;

and the occasional preservation in the two countries of the most useful

animals would ultimately lead to the formation of two widely distinct

breeds.

* * * * *

With plants, from the earliest dawn of civilisation, the best variety which

at each period was known would generally have been cultivated and its seeds

occasionally sown; so that there will have been some selection from an

extremely remote period, but without any prefixed standard of excellence or

thought of the future. We at the present day profit by a course of

selection occasionally and unconsciously carried on during thousands of

years. This is proved in an interesting manner by Oswald Heer's researches

on the lake-inhabitants of Switzerland, as given in a former chapter; for

he shows that the grain and seed of our present varieties of wheat, barley,

oats, peas, beans, lentils, and poppy, exceed in size those which were

cultivated in Switzerland during the Neolithic and Bronze periods. These

ancient people, during the Neolithic period, possessed also a crab

considerably larger than that now growing wild on the Jura.[522] The pears

described by Pliny were evidently extremely inferior in quality to our

present pears. We can realise the effects of long-continued selection and

cultivation in another way, for would any one in his senses expect to raise

a first-rate apple from the seed of a truly wild crab, or a luscious

melting pear from the wild pear? Alphonse De Candolle informs me that he

has lately seen on an ancient mosaic at Rome a representation of {216} the

melon; and as the Romans, who were such gourmands, are silent on this

fruit, he infers that the melon has been greatly ameliorated since the

classical period.