The indirect evidence in favour of the Pallasian doctrine appears to me to

be extremely strong. In the earlier chapters I have attempted to show that

our various breeds of dogs are descended from several wild species; and

this probably is the case with sheep. There can no longer be any doubt that

the Zebu or humped Indian ox belongs to a distinct species from European

cattle: the latter, moreover, are descended from two or three forms, which

may be called either species or wild races, but which co-existed in a state

of nature and kept distinct. We have good evidence that our domesticated

pigs belong to at least two specific types, _S. scrofa_ and _Indica_, which

probably lived together in a wild state in South-eastern Europe. Now, a

widely-extended analogy leads to the belief that if these several allied

species, in the wild state or when first reclaimed, had been crossed, they

would have exhibited, both in their first unions and in their hybrid

offspring, some degree of sterility. Nevertheless the several domesticated

races descended from them are now all, as far as can be ascertained,

perfectly fertile together. If this reasoning be trustworthy, and it is

apparently sound, we must admit the Pallasian doctrine that long-continued

domestication tends to eliminate that sterility which is natural to species

when crossed in their aboriginal state.

{111}

_On increased Fertility from Domestication and Cultivation._

Increased fertility from domestication, without any reference to crossing,

may be here briefly considered. This subject bears indirectly on two or

three points connected with the modification of organic beings. As Buffon

long ago remarked,[242] domestic animals breed oftener in the year and

produce more young at a birth than wild animals of the same species; they,

also, sometimes breed at an earlier age. The case would hardly have

deserved further notice, had not some authors lately attempted to show that

fertility increases and decreases in an inverse ratio with the amount of

food. This strange doctrine has apparently arisen from individual animals

when supplied with an inordinate quantity of food, and from plants of many

kinds when grown on excessively rich soil, as on a dunghill, becoming

sterile; but to this latter point I shall have occasion presently to

return. With hardly an exception, our domesticated animals, which have long

been habituated to a regular and copious supply of food, without the labour

of searching for it, are more fertile than the corresponding wild animals.

It is notorious how frequently cats and dogs breed, and how many young they

produce at a birth. The wild rabbit is said generally to breed four times

yearly, and to produce from four to eight young; the tame rabbit breeds six

or seven times yearly, and produces from four to eleven young. The ferret,

though generally so closely confined, is more prolific than its supposed

wild prototype. The wild sow is remarkably prolific, for she often breeds

twice in the year, and produces from four to eight and sometimes even

twelve young at a birth; but the domestic sow regularly breeds twice a

year, and would breed oftener if permitted; and a sow that produces less

than eight at a birth "is worth little, and the sooner she is fattened for

the butcher the better." The amount of food affects the fertility even of

the same individual: thus sheep, which on mountains never produce more than

one lamb at a birth, when brought {112} down to lowland pastures frequently

bear twins. This difference apparently is not due to the cold of the higher

land, for sheep and other domestic animals are said to be extremely

prolific in Lapland. Hard living, also, retards the period at which animals

conceive; for it has been found disadvantageous in the northern islands of

Scotland to allow cows to bear calves before they are four years old.[243]

Birds offer still better evidence of increased fertility from

domestication: the hen of the wild _Gallus bankiva_ lays from six to

ten eggs, a number which would be thought nothing of with the domestic

hen. The wild duck lays from five to ten eggs; the tame one in the

course of the year from eighty to one hundred. The wild grey-lag goose

lays from five to eight eggs; the tame from thirteen to eighteen, and

she lays a second time; as Mr. Dixon has remarked, "high-feeding, care,

and moderate warmth induce a habit of prolificacy which becomes in some

measure hereditary." Whether the semi-domesticated dovecot pigeon is

more fertile than the wild rock-pigeon _C. livia_, I know not; but the

more thoroughly domesticated breeds are nearly twice as fertile as

dovecots: the latter, however, when caged and highly fed, become

equally fertile with house pigeons. The peahen alone of domesticated

birds is rather more fertile, according to some accounts, when wild in

its native Indian home, than when domesticated in Europe and exposed to

our much colder climate.[244]

With respect to plants, no one would expect wheat to tiller more, and

each ear to produce more grain, in poor than in rich soil; or to get in

poor soil a heavy crop of peas or beans. Seeds vary so much in number

{113} that it is difficult to estimate them; but on comparing beds of

carrots saved for seed in a nursery garden with wild plants, the former

seemed to produce about twice as much seed. Cultivated cabbages yielded

thrice as many pods by measure as wild cabbages from the rocks of South

Wales. The excess of berries produced by the cultivated Asparagus in

comparison with the wild plant is enormous. No doubt many highly

cultivated plants, such as pears, pineapples, bananas, sugar-cane, &c.,

are nearly or quite sterile; and I am inclined to attribute this

sterility to excess of food and to other unnatural conditions; but to

this subject I shall presently recur.

In some cases, as with the pig, rabbit, &c., and with those plants which

are valued for their seed, the direct selection of the more fertile

individuals has probably much increased their fertility; and in all cases

this may have occurred indirectly, from the better chance of the more

numerous offspring produced by the more fertile individuals having

survived. But with cats, ferrets, and dogs, and with plants like carrots,

cabbages, and asparagus, which are not valued for their prolificacy,

selection can have played only a subordinate part; and their increased

fertility must be attributed to the more favourable conditions of life

under which they have long existed.

* * * * *

{114}

CHAPTER XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF CLOSE

INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID

TENDENCIES--GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING,

AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING--CATTLE, CLOSELY

INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME

PARKS--SHEEP--FALLOW-DEER--DOGS--RABBITS--PIGS--MAN, ORIGIN OF HIS

ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS,

GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS,

FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED

SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON

CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT,

BUT ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH

DISTINCT INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES--CONCLUSION.

The gain in constitutional vigour, derived from an occasional cross between

individuals of the same variety, but belonging to distinct families, or

between distinct varieties, has not been so largely or so frequently

discussed, as have the evil effects of too close interbreeding. But the

former point is the more important of the two, inasmuch as the evidence is

more decisive. The evil results from close interbreeding are difficult to

detect, for they accumulate slowly, and differ much in degree with

different species; whilst the good effects which almost invariably follow a

cross are from the first manifest. It should, however, be clearly

understood that the advantage of close interbreeding, as far as the

retention of character is concerned, is indisputable, and often outweighs

the evil of a slight loss of constitutional vigour. In relation to the

subject of domestication, the whole question is of some importance, as too

close interbreeding interferes with the improvement of old races, and

especially with the formation of new ones. It is important as indirectly

bearing on Hybridism; and perhaps on the extinction of species, when any

form has become so rare that only a few individuals {115} remain within a

confined area. It bears in an important manner on the influence of free

intercrossing, in obliterating individual differences, and thus giving

uniformity of character to the individuals of the same race or species; for

if additional vigour and fertility be thus gained, the crossed offspring

will multiply and prevail, and the ultimate result will be far greater than

otherwise would have occurred. Lastly, the question is of high interest, as

bearing on mankind. Hence I shall discuss this subject at full length. As

the facts which prove the evil effects of close interbreeding are more

copious, though less decisive, than those on the good effects of crossing,

I shall, under each group of beings, begin with the former.

There is no difficulty in defining what is meant by a cross; but this is by

no means easy in regard to "breeding in and in" or "too close

interbreeding," because, as we shall see, different species of animals are

differently affected by the same degree of interbreeding. The pairing of a

father and daughter, or mother and son, or brothers and sisters, if carried

on during several generations, is the closest possible form of

interbreeding. But some good judges, for instance Sir J. Sebright, believe

that the pairing of a brother and sister is closer than that of parents and

children; for when the father is matched with his daughter he crosses, as

is said, with only half his own blood. The consequences of close

interbreeding carried on for too long a time, are, as is generally

believed, loss of size, constitutional vigour, and fertility, sometimes

accompanied by a tendency to malformation. Manifest evil does not usually

follow from pairing the nearest relations for two, three, or even four

generations; but several causes interfere with our detecting the evil--such

as the deterioration being very gradual, and the difficulty of

distinguishing between such direct evil and the inevitable augmentation of

any morbid tendencies which may be latent or apparent in the related

parents. On the other hand, the benefit from a cross, even when there has

not been any very close interbreeding, is almost invariably at once

conspicuous. There is reason to believe, and this was the opinion of that

most experienced observer Sir J. Sebright,[245] that the evil effects of

close interbreeding may be checked by the related individuals {116} being

separated during a few generations and exposed to different conditions of

life.

That evil directly follows from any degree of close interbreeding has been

denied by many persons; but rarely by any practical breeder; and never, as

far as I know, by one who has largely bred animals which propagate their

kind quickly. Many physiologists attribute the evil exclusively to the

combination and consequent increase of morbid tendencies common to both

parents: that this is an active source of mischief there can be no doubt.

It is unfortunately too notorious that men and various domestic animals

endowed with a wretched constitution, and with a strong hereditary

disposition to disease, if not actually ill, are fully capable of

procreating their kind. Close interbreeding, on the other hand, induces

sterility; and this indicates something quite distinct from the

augmentation of morbid tendencies common to both parents. The evidence

immediately to be given convinces me that it is a great law of nature, that

all organic beings profit from an occasional cross with individuals not

closely related to them in blood; and that, on the other hand,

long-continued close interbreeding is injurious.

Various general considerations have had much influence in leading me to

this conclusion; but the reader will probably rely more on special facts

and opinions. The authority of experienced observers, even when they do not

advance the grounds of their belief, is of some little value. Now almost

all men who have bred many kinds of animals and have written on the

subject, such as Sir J. Sebright, Andrew Knight, &c.,[246] have expressed

the strongest conviction on the impossibility of long-continued close

interbreeding. Those who have compiled works on agriculture, and have

associated much with breeders, such as the sagacious Youatt, Low, &c., have

strongly declared their opinion to the same effect. Prosper Lucas, trusting

largely to French authorities, has come to a similar conclusion. The

distinguished German agriculturist Hermann von Nathusius, who has written

the most able treatise on this subject which I have met with, concurs; and

as I shall have to quote from {117} this treatise, I may state that

Nathusius is not only intimately acquainted with works on agriculture in

all languages, and knows the pedigrees of our British breeds better than

most Englishmen, but has imported many of our improved animals, and is

himself an experienced breeder.

Evidence of the evil effects of close interbreeding can most readily be

acquired in the case of animals, such as fowls, pigeons, &c., which

propagate quickly, and, from being kept in the same place, are exposed to

the same conditions. Now I have inquired of very many breeders of these

birds, and I have hitherto not met with a single man who was not thoroughly

convinced that an occasional cross with another strain of the same

sub-variety was absolutely necessary. Most breeders of highly-improved or

fancy birds value their own strain, and are most unwilling, at the risk, in

their opinion, of deterioration, to make a cross. The purchase of a

first-rate bird of another strain is expensive, and exchanges are

troublesome; yet all breeders, as far as I can hear, excepting those who

keep large stocks at different places for the sake of crossing, are driven

after a time to take this step.

Another general consideration which has had great influence on my mind is,

that with all hermaphrodite animals and plants, which it might have been

thought would have perpetually fertilised themselves, and thus have been

subjected for long ages to the closest interbreeding, there is no single

species, as far as I can discover, in which the structure ensures

self-fertilisation. On the contrary, there are in a multitude of cases, as

briefly stated in the fifteenth chapter, manifest adaptations which favour

or inevitably lead to an occasional cross between one hermaphrodite and

another of the same species; and these adaptive structures are utterly

purposeless, as far as we can see, for any other end.

With _Cattle_ there can be no doubt that extremely close interbreeding

may be long carried on, advantageously with respect to external

characters and with no manifestly apparent evil as far as constitution

is concerned. The same remark is applicable to sheep. Whether these

animals have gradually been rendered less susceptible than others to

this evil, in order to permit them to live in herds,--a habit which

leads the old and vigorous males to expel all intruders, and in

consequence often to pair with their own daughters, I will not pretend

to decide. The case of Bakewell's Long-horns, which were closely

interbred for a long period, has often been {118} quoted; yet Youatt

says[247] the breed "had acquired a delicacy of constitution

inconsistent with common management," and "the propagation of the

species was not always certain." But the Shorthorns offer the most

striking case of close interbreeding; for instance, the famous bull

Favourite (who was himself the offspring of a half-brother and sister

from Foljambe) was matched with his own daughter, granddaughter, and

great-granddaughter; so that the produce of this last union, or the

great-great-granddaughter, had 15-16ths, or 93.75 per cent. of the

blood of Favourite in her veins. This cow was matched with the bull

Wellington, having 62.5 per cent. of Favourite blood in his veins, and

produced Clarissa; Clarissa was matched with the bull Lancaster, having

68.75 of the same blood, and she yielded valuable offspring.[248]

Nevertheless Collings, who reared these animals, and was a strong

advocate for close breeding, once crossed his stock with a Galloway,

and the cows from this cross realised the highest prices. Bates's herd

was esteemed the most celebrated in the world. For thirteen years he

bred most closely in and in; but during the next seventeen years,

though he had the most exalted notion of the value of his own stock, he

thrice infused fresh blood into his herd: it is said that he did this,

not to improve the form of his animals, but on account of their

lessened fertility. Mr. Bates's own view, as given by a celebrated

breeder,[249] was, that "to breed in and in from a bad stock was ruin

and devastation; yet that the practice may be safely followed within

certain limits when the parents so related are descended from

first-rate animals." We thus see that there has been extremely close

interbreeding with Shorthorns; but Nathusius, after the most careful

study of their pedigrees, says that he can find no instance of a

breeder who has strictly followed this practice during his whole life.

From this study and his own experience, he concludes that close

interbreeding is necessary to ennoble the stock; but that in effecting

this the greatest care is necessary, on account of the tendency to

infertility and weakness. It may be added, that another high

authority[250] asserts that many more calves are born cripples from

Shorthorns than from other and less closely interbred races of cattle.

Although by carefully selecting the best animals (as Nature effectually

does by the law of battle) close interbreeding may be long carried on

with cattle, yet the good effects of a cross between almost any two

breeds is at once shown by the greater size and vigour of the

offspring; as Mr. Spooner writes to me, "crossing distinct breeds

certainly improves cattle for the butcher." Such crossed animals are of

course of no value to the breeder; but they have been raised during

many years in several {119} parts of England to be slaughtered;[251]

and their merit is now so fully recognised, that at fat-cattle shows a

separate class has been formed for their reception. The best fat ox at

the great show at Islington in 1862 was a crossed animal.

The half-wild cattle, which have been kept in British parks probably

for 400 or 500 years, or even for a longer period, have been advanced

by Culley and others as a case of long-continued interbreeding within

the limits of the same herd without any consequent injury. With respect

to the cattle at Chillingham, the late Lord Tankerville owned that they

were bad breeders.[252] The agent, Mr. Hardy, estimates (in a letter to

me, dated May, 1861) that in the herd of about fifty the average number

annually slaughtered, killed by fighting, and dying, is about ten, or

one in five. As the herd is kept up to nearly the same average number,

the annual rate of increase must be likewise about one in five. The

bulls, I may add, engage in furious battles, of which battles the

present Lord Tankerville has given me a graphic description, so that

there will always be rigorous selection of the most vigorous males. I

procured in 1855 from Mr. D. Gardner, agent to the Duke of Hamilton,

the following account of the wild cattle kept in the Duke's park in

Lanarkshire, which is about 200 acres in extent. The number of cattle

varies from sixty-five to eighty; and the number annually killed (I

presume by all causes) is from eight to ten; so that the annual rate of

increase can hardly be more than one in six. Now in South America,

where the herds are half-wild, and therefore offer a nearly fair

standard of comparison, according to Azara the natural increase of the

cattle on an estancia is from one-third to one-fourth of the total

number, or one in between three and four; and this, no doubt, applies

exclusively to adult animals fit for consumption. Hence the half-wild

British cattle which have long interbred within the limits of the same

herd are relatively far less fertile. Although in an unenclosed country

like Paraguay there must be some crossing between the different herds,

yet even there the inhabitants believe that the occasional introduction

of animals from distant localities is necessary to prevent

"degeneration in size and diminution of fertility."[253] The decrease

in size from ancient times in the Chillingham and Hamilton cattle must

have been prodigious, for Professor Ruetimeyer has shown that they are

almost certainly the descendants of the gigantic _Bos primigenius_. No

doubt this decrease in size may be largely attributed to less

favourable conditions of life; yet animals roaming over large parks,

and fed during severe winters, can hardly be considered as placed under

very unfavourable conditions.

With _Sheep_ there has often been long-continued interbreeding within

the limits of the same flock; but whether the nearest relations have

been matched so frequently as in the case of Shorthorn cattle, I do not

know. The Messrs. Brown during fifty years have never infused fresh

blood into their excellent flock of Leicesters. Since 1810 Mr. Barford

has acted on the same principle with the Foscote flock. He asserts that

half a century {120} of experience has convinced him that when two

nearly related animals are quite sound in constitution, in-and-in

breeding does not induce degeneracy; but he adds that he "does not

pride himself on breeding from the nearest affinities." In France the

Naz flock has been bred for sixty years without the introduction of a

single strange ram.[254] Nevertheless, most great breeders of sheep

have protested against close interbreeding prolonged for too great a

length of time.[255] The most celebrated of recent breeders, Jonas

Webb, kept five separate families to work on, thus "retaining the

requisite distance of relationship between the sexes."[256]

Although by the aid of careful selection the near interbreeding of

sheep may be long continued without any manifest evil, yet it has often

been the practice with farmers to cross distinct breeds to obtain

animals for the butcher, which plainly shows that good is derived from

this practice. Mr. Spooner sums up his excellent Essay on Crossing by

asserting that there is a direct pecuniary advantage in judicious

cross-breeding, especially when the male is larger than the female. A

former celebrated breeder, Lord Somerville, distinctly states that his

half-breeds from Ryelands and Spanish sheep were larger animals than

either the pure Ryelands or pure Spanish sheep.[257]

As some of our British parks are ancient, it occurred to me that there

must have been long-continued close interbreeding with the fallow deer

(_Cervus dama_) kept in them; but on inquiry I find that it is a common

practice to infuse new blood by procuring bucks from other parks. Mr.

Shirley,[258] who has carefully studied the management of deer, admits

that in some parks there has been no admixture of foreign blood from a

time beyond the memory of man. But he concludes "that in the end the

constant breeding in-and-in is sure to tell to the disadvantage of the

whole herd, though it may take a very long time to prove it; moreover,

when we find, as is very constantly the case, that the introduction of

fresh blood has been of the very greatest use to deer, both by

improving their size and appearance, and particularly by being of

service in removing the taint of 'rickback,' if not of other diseases,

to which deer are sometimes subject when the blood has not been

changed, there can, I think, be no doubt but that a judicious cross

with a good stock is of the greatest consequence, and is indeed

essential, sooner or later, to the prosperity of every well-ordered

park."

Mr. Meynell's famous foxhounds have been adduced, as showing that no

ill effects follow from close interbreeding; and Sir J. Sebright

ascertained from him that he frequently bred from father and daughter,

mother and {121} son, and sometimes even from brothers and sisters. Sir

J. Sebright, however, declares,[259] that by breeding _in-and-in_, by

which he means matching brothers and sisters, he has actually seen

strong spaniels become weak and diminutive lapdogs. The Rev. W. D. Fox

has communicated to me the case of a small lot of bloodhounds, long

kept in the same family, which had become very bad breeders, and nearly

all had a bony enlargement in the tail. A single cross with a distinct

strain of bloodhounds restored their fertility, and drove away the

tendency to malformation in the tail. I have heard the particulars of

another case with bloodhounds, in which the female had to be held to

the male. Considering how rapid is the natural increase of the dog, it

is difficult to understand the high price of most highly improved

breeds, which almost implies long-continued close interbreeding, except

on the belief that this process lessens fertility and increases

liability to distemper and other diseases. A high authority, Mr.

Scrope, attributes the rarity and deterioration in size of the Scotch

deerhound (the few individuals now existing throughout the country

being all related) in large part to close interbreeding.

With all highly-bred animals there is more or less difficulty in

getting them to procreate quickly, and all suffer much from delicacy of

constitution; but I do not pretend that these effects ought to be

wholly attributed to close interbreeding. A great judge of rabbits[260]

says, "the long-eared does are often too highly bred or forced in their

youth to be of much value as breeders, often turning out barren or bad

mothers." Again: "Very long-eared bucks will also sometimes prove

barren." These highly-bred rabbits often desert their young, so that it

is necessary to have nurse-rabbits.

With _Pigs_ there is more unanimity amongst breeders on the evil

effects of close interbreeding than, perhaps, with any other large

animal. Mr. Druce, a great and successful breeder of the Improved

Oxfordshires (a crossed race), writes, "without a change of boars of a

different tribe, but of the same breed, constitution cannot be

preserved." Mr. Fisher Hobbs, the raiser of the celebrated Improved

Essex breed, divided his stock into three separate families, by which

means he maintained the breed for more than twenty years, "by judicious

selection from the _three distinct families_."[261] Lord Western was

the first importer of a Neapolitan boar and sow. "From this pair he

bred in-and-in, until the breed was in danger of becoming extinct, a

sure result (as Mr. Sidney remarks) of in-and-in breeding." Lord

Western then crossed his Neapolitan pigs with the old Essex, and made

the first great step towards the Improved Essex breed. Here is a more

interesting case. Mr. J. Wright, well known as a breeder, crossed[262]

the same boar with the daughter, granddaughter, and

great-granddaughter, and so on for seven generations. The result was,

that in many instances the offspring failed to breed; in others they

produced few that lived; and of the latter many were idiotic, without

sense {122} even to suck, and when attempting to move could not walk

straight. Now it deserves especial notice, that the two last sows

produced by this long course of interbreeding were sent to other boars,

and they bore several litters of healthy pigs. The best sow in external

appearance produced during the whole seven generations was one in the

last stage of descent; but the litter consisted of this one sow. She

would not breed to her sire, yet bred at the first trial to a stranger

in blood. So that, in Mr. Wright's case, long-continued and extremely

close interbreeding did not affect the external form or merit of the

young; but with many of them the general constitution and mental

powers, and especially the reproductive functions, were seriously

affected.

Nathusius gives[263] an analogous and even more striking case: he

imported from England a pregnant sow of the large Yorkshire breed, and

bred the product closely in-and-in for three generations: the result

was unfavourable, as the young were weak in constitution, with impaired

fertility. One of the latest sows, which he esteemed a good animal,

produced, when paired with her own uncle (who was known to be

productive with sows of other breeds), a litter of six, and a second

time a litter of only five weak young pigs. He then paired this sow

with a boar of a small black breed, which he had likewise imported from

England, and which boar, when matched with sows of his own breed,

produced from seven to nine young: now, the sow of the large breed,

which was so unproductive when paired with her own uncle, yielded to

the small black boar, in the first litter twenty-one, and in the second

litter eighteen young pigs; so that in one year she produced

thirty-nine fine young animals!

As in the case of several other animals already mentioned, even when no

injury is perceptible from moderately close interbreeding, yet, to

quote the words of Mr. Coate, a most successful breeder (who five times

won the annual gold medal of the Smithfield Club Show for the best pen

of pigs), "Crosses answer well for profit to the farmer, as you get

more constitution and quicker growth; but for me, who sell a great

number of pigs for breeding purposes, I find it will not do, as it

requires many years to get anything like purity of blood again."[264]

Before passing on to Birds, I ought to refer to man, though I am unwilling

to enter on this subject, as it is surrounded by natural prejudices. It has

moreover been discussed by various authors under many points of view.[265]

Mr. Tylor[266] has shown {123} that with widely different races, in the

most distant quarters of the world, marriages between relations--even

between distant relations--have been strictly prohibited. A few exceptional

cases can be specified, especially with royal families; and these have been

enlarged on in a learned article[267] by Mr. W. Adam, and formerly in 1828

by Hofacker. Mr. Tylor is inclined to believe that the almost universal

prohibition of closely-related marriages has arisen from their evil effects

having been observed, and he ingeniously explains some apparent anomalies

in the prohibition not extending equally to the relations on both the male

and female side. He admits, however, that other causes, such as the

extension of friendly alliances, may have come into play. Mr. W. Adam, on

the other hand, concludes that related marriages are prohibited and viewed

with repugnance from the confusion which would thus arise in the descent of

property, and from other still more recondite reasons; but I cannot accept

this view, seeing that the savages of Australia and South America,[268] who

have no property to bequeath or fine moral feelings to confuse, hold the

crime of incest in abhorrence.

It would be interesting to know, if it could be ascertained, as throwing

light on this question with respect to man, what occurs with the higher

anthropomorphous apes--whether the young males and females soon wander away

from their parents, or whether the old males become jealous of their sons

and expel them, or whether any inherited instinctive feeling, from being

beneficial, has been generated, leading the young males and females of the

same family to prefer pairing with distinct families, and to dislike

pairing with each other. A considerable body of evidence has already been

advanced, showing that the offspring from parents which are not related are

more vigorous and fertile than those from parents which are closely

related; hence any slight feeling, arising from the sexual excitement of

novelty or other cause, which led to the former rather than to the latter

unions, would be augmented through natural selection, and thus might become

instinctive; for those individuals which had an innate preference of this

kind would increase in number. It seems more probable, that degraded

savages should {124} thus unconsciously have acquired their dislike and

even abhorrence of incestuous marriages, rather than that they should have

discovered by reasoning and observation the evil results. The abhorrence

occasionally failing is no valid argument against the feeling being

instinctive, for any instinct may occasionally fail or become vitiated, as

sometimes occurs with parental love and the social sympathies. In the case

of man, the question whether evil follows from close interbreeding will

probably never be answered by direct evidence, as he propagates his kind so

slowly and cannot be subjected to experiment; but the almost universal

practice of all races at all times of avoiding closely-related marriages is

an argument of considerable weight; and whatever conclusion we arrive at in

regard to the higher animals may be safely extended to man.

Turning now to Birds: in the case of the _Fowl_ a whole array of

authorities could be given against too close interbreeding. Sir J.

Sebright positively asserts that he made many trials, and that his

fowls, when thus treated, became long in the legs, small in the body,

and bad breeders.[269] He produced the famous Sebright Bantams by

complicated crosses, and by breeding in-and-in; and since his time

there has been much close interbreeding with these Bantams; and they

are now notoriously bad breeders. I have seen Silver Bantams, directly

descended from his stock, which had become almost as barren as hybrids;

for not a single chicken had been that year hatched from two full nests

of eggs. Mr. Hewitt says that with these Bantams the sterility of the

male stands, with rare exceptions, in the closest relation with their

loss of certain secondary male characters: he adds, "I have noticed, as

a general rule, that even the slightest deviation from feminine

character in the tail of the male Sebright--say the elongation by only

half an inch of the two principal tail-feathers--brings with it

improved probability of increased fertility."[270]

Mr. Wright states[271] that Mr. Clark, "whose fighting-cocks were so

notorious, continued to breed from his own kind till they lost their

disposition to fight, but stood to be cut up without making any

resistance, and were so reduced in size as to be under those weights

required for the best prizes; but on obtaining a cross from Mr.

Leighton, they again resumed their former courage and weight." It

should be borne in mind that game-cocks before they fought were always

weighed, so that nothing was left to the imagination about any

reduction or increase of {125} weight. Mr. Clark does not seem to have

bred from brothers and sisters, which is the most injurious kind of

union; and he found, after repeated trials, that there was a greater

reduction in weight in the young from a father paired with his

daughter, than from a mother with her son. I may add that Mr. Eyton, of

Eyton, the well-known ornithologist, who is a large breeder of Grey

Dorkings, informs me that they certainly diminish in size, and become

less prolific, unless a cross with another strain is occasionally

obtained. So it is with Malays, according to Mr. Hewitt, as far as size

is concerned.[272]

An experienced writer[273] remarks that the same amateur, as is well

known, seldom long maintains the superiority of his birds; and this, he

adds, undoubtedly is due to all his stock "being of the same blood;"

hence it is indispensable that he should occasionally procure a bird of

another strain. But this is not necessary with those who keep a stock

of fowls at different stations. Thus, Mr. Ballance, who has bred Malays

for thirty years, and has won more prizes with these birds than any

other fancier in England, says that breeding in-and-in does not

necessarily cause deterioration; "but all depends upon how this is

managed." "My plan has been to keep about five or six distinct runs,

and to rear about two hundred or three hundred chickens each year, and

select the best birds from each run for crossing. I thus secure

sufficient crossing to prevent deterioration."[274]

We thus see that there is almost complete unanimity with

poultry-breeders that, when fowls are kept at the same place, evil

quickly follows from interbreeding carried on to an extent which would

be disregarded in the case of most quadrupeds. On the other hand, it is

a generally received opinion that cross-bred chickens are the hardiest

and most easily reared.[275] Mr. Tegetmeier, who has carefully attended

to poultry of all breeds, says[276] that Dorking hens, allowed to run

with Houdan or Crevecoeur cocks, "produce in the early spring chickens

that for size, hardihood, early maturity, and fitness for the market,

surpass those of any pure breed that we have ever raised." Mr. Hewitt

gives it as a general rule with fowls, that crossing the breed

increases their size. He makes this remark after stating that hybrids

from the pheasant and fowl are considerably larger than either

progenitor: so again, hybrids from the male golden pheasant and hen

common pheasant "are of far larger size than either parent-bird."[277]

To this subject of the increased size of hybrids I shall presently

return.

With _Pigeons_, breeders are unanimous, as previously stated, that it

is absolutely indispensable, notwithstanding the trouble and expense

thus caused, occasionally to cross their much-prized birds with

individuals of another strain, but belonging, of course, to the same

variety. It deserves {126} notice that, when large size is one of the

desired characters, as with pouters,[278] the evil effects of close

interbreeding are much sooner perceived than when small birds, such as

short-faced tumblers, are valued. The extreme delicacy of the high

fancy breeds, such as these tumblers and improved English carriers, is

remarkable; they are liable to many diseases, and often die in the egg

or during the first moult; and their eggs have generally to be hatched

under foster-mothers. Although these highly-prized birds have

invariably been subjected to much close interbreeding, yet their

extreme delicacy of constitution cannot perhaps be thus fully

explained. Mr. Yarrell informed me that Sir J. Sebright continued

closely interbreeding some owl-pigeons, until from their extreme

sterility he as nearly as possible lost the whole family. Mr.

Brent[279] tried to raise a breed of trumpeters, by crossing a common

pigeon, and recrossing the daughter, granddaughter,

great-granddaughter, and great-great-granddaughter, with the same male

trumpeter, until he obtained a bird with 15/16ths of trumpeter's blood;

but then the experiment failed, for "breeding so close stopped

reproduction." The experienced Neumeister[280] also asserts that the

offspring from dovecotes and various other breeds are "generally very

fertile and hardy birds:" so again, MM. Boitard and Corbie,[281] after

forty-five years' experience, recommend persons to cross their breeds

for amusement; for, if they fail to make interesting birds, they will

succeed under an economical point of view, "as it is found that

mongrels are more fertile than pigeons of pure race."

I will refer only to one other animal, namely, the Hive-bee, because a

distinguished entomologist has advanced this as a case of inevitable

close interbreeding. As the hive is tenanted by a single female, it

might have been thought that her male and female offspring would always

have bred together, more especially as bees of different hives are

hostile to each other; a strange worker being almost always attacked

when trying to enter another hive. But Mr. Tegetmeier has shown[282]

that this instinct does not apply to drones, which are permitted to

enter any hive; so that there is no _a priori_ improbability of a queen

receiving a foreign drone. The fact of the union invariably and

necessarily taking place on the wing, during the queen's nuptial

flight, seems to be a special provision against continued

interbreeding. However this may be, experience has shown, since the

introduction of the yellow-banded Ligurian race into Germany and

England, that bees freely cross: Mr. Woodbury, who introduced Ligurian

bees into Devonshire, found during a single season that three stocks,

at distances of from one to two miles from his hives, were crossed by

his drones. In one case the Ligurian drones must have flown over the

city of Exeter, and over several intermediate hives. On another

occasion several common black queens were crossed by Ligurian drones at

a distance of from one to three and a half miles.[283]

{127}

_Plants._

When a single plant of a new species is introduced into any country, if

propagated by seed, many individuals will soon be raised, so that if

the proper insects be present there will be crossing. With

newly-introduced trees or other plants not propagated by seed we are

not here concerned. With old-established plants it is an almost

universal practice occasionally to make exchanges of seed, by which

means individuals which have been exposed to different conditions of

life,--and this, as we have seen, diminishes the evil from close

interbreeding,--will occasionally be introduced into each district.

Experiments have not been tried on the effects of fertilising flowers

with their own pollen during _several_ generations. But we shall

presently see that certain plants, either normally or abnormally, are

more or less sterile, even in the first generation, when fertilised by

their own pollen. Although nothing is directly known on the evil

effects of long-continued close interbreeding with plants, the converse

proposition that great good is derived from crossing is well

established.

With respect to the crossing of individuals belonging to the same

sub-variety, Gaertner, whose accuracy and experience exceeded that of

all other hybridisers, states[284] that he has many times observed good

effects from this step, especially with exotic genera, of which the

fertility is somewhat impaired, such as Passiflora, Lobelia, and

Fuchsia. Herbert also says,[285] "I am inclined to think that I have

derived advantage from impregnating the flower from which I wished to

obtain seed with pollen from another individual of the same variety, or

at least from another flower, rather than with its own." Again,

Professor Lecoq asserts that he has ascertained that crossed offspring

are more vigorous and robust than their parents.[286]

General statements of this kind, however, can seldom be fully trusted;

consequently I have begun a series of experiments, which, if they

continue to give the same results as hitherto, will for ever settle the

question of the good effects of crossing two distinct plants of the

same variety, and of the evil effects of self-fertilisation. A clear

light will thus also be thrown on the fact that flowers are invariably

constructed so as to permit, or favour, or necessitate the union of two

individuals. We shall clearly understand why monoecious and

dioecious,--why dimorphic and trimorphic plants exist, and many other

such cases. The plan which I have followed in my experiments is to grow

plants in the same pot, or in pots of the same size, or close together

in the open ground; to carefully exclude insects; and then to fertilise

some of the flowers with pollen from the same flower, and others on the

same plant with pollen from a distinct but adjoining plant. In many,

but not all, of these experiments, the crossed plants yielded much more

seed than the self-fertilised plants; and I have never seen the {128}

reversed case. The self-fertilised and crossed seeds thus obtained were

allowed to germinate in the same glass vessel on damp sand; and as the

seeds successively germinated, they were planted in pairs on opposite

sides of the same pot, with a superficial partition between them, and

were placed so as to be equally exposed to the light. In other cases

the self-fertilised and crossed seeds were simply sown on opposite

sides of the same small pot. I have, in short, followed different

plans, but in every case have taken all the precautions which I could

think of, so that the two lots should be equally favoured. Now, I have

carefully observed the growth of plants raised from crossed and

self-fertilised seed, from their germination to maturity, in species of

the following genera, namely, Brassica, Lathyrus, Lupinus, Lobelia,

Lactuca, Dianthus, Myosotis, Petunia, Linaria, Calceolaria, Mimulus,

and Ipomoea, and the difference in their powers of growth, and of

withstanding in certain cases unfavourable conditions, was most

manifest and strongly marked. It is of importance that the two lots of

seed should be sown or planted on opposite sides of the same pot, so

that the seedlings may struggle against each other; for if sown

separately in ample and good soil, there is often but little difference

in their growth.

I will briefly describe the two most striking cases as yet observed by

me. Six crossed and six self-fertilised seeds of _Ipomoea purpurea_,

from plants treated in the manner above described, were planted as soon

as they had germinated, in pairs on opposite sides of two pots, and

rods of equal thickness were given them to twine up. Five of the

crossed plants grew from the first more quickly than the opposed

self-fertilised plants; the sixth, however, was weakly and was for a

time beaten, but at last its sounder constitution prevailed and it shot

ahead of its antagonist. As soon as each crossed plant reached the top

of its seven-foot rod its fellow was measured, and the result was that,

when the crossed plants were seven feet high, the self-fertilised had

attained the average height of only five feet four and a half inches.

The crossed plants flowered a little before, and more profusely than

the self-fertilised plants. On opposite sides of another _small_ pot a

large number of crossed and self-fertilised seeds were sown, so that

they had to struggle for bare existence; a single rod was given to each

lot: here again the crossed plants showed from the first their

advantage; they never quite reached the summit of the seven-foot rod,

but relatively to the self-fertilised plants their average height was

as seven feet to five feet two inches. The experiment was repeated in

the two following generations with plants raised from the

self-fertilised and crossed plants, treated in exactly the same manner,

and with nearly the same result. In the second generation, the crossed

plants, which were again crossed, produced 121 seed-capsules, whilst

the self-fertilised plants, again self-fertilised, produced only 84

capsules.

Some flowers of the _Mimulus luteus_ were fertilised with their own

pollen, and others were crossed with pollen from distinct plants

growing in the same pot. The seeds after germinating were thickly

planted on opposite sides of a pot. The seedlings were at first equal

in height; but when the young crossed plants were exactly half an inch,

the {129} self-fertilised plants were only a quarter of an inch high.

But this inequality did not continue, for, when the crossed plants were

four and a half inches high, the self-fertilised were three inches; and

they retained the same relative difference till their growth was

complete. The crossed plants looked far more vigorous than the

uncrossed, and flowered before them; they produced also a far greater

number of flowers, which yielded capsules (judging, however, from only

a few) containing more seeds. As in the former case, the experiment was

repeated in the same manner during the next two generations, and with

exactly the same result. Had I not watched these plants of the Mimulus

and Ipomoea during their whole growth, I could not have believed it

possible, that a difference apparently so slight, as that of the pollen

being taken from the same flower, and from a distinct plant growing in

the same small pot, could have made so wonderful a difference in the

growth and vigour of the plants thus produced. This, under a

physiological point of view, is a most remarkable phenomenon.

* * * * *

With respect to the benefit derived from crossing distinct varieties,

plenty of evidence has been published. Sageret[287] repeatedly speaks

in strong terms of the vigour of melons raised by crossing different

varieties, and adds that they are more easily fertilised than common

melons, and produce numerous good seed. Here follows the evidence of an

English gardener:[288] "I have this summer met with better success in

my cultivation of melons, in an unprotected state, from the seeds of

hybrids (_i.e._ mongrels) obtained by cross impregnation, than with old

varieties. The offspring of three different hybridisations (one more

especially, of which the parents were the two most dissimilar varieties

I could select) each yielded more ample and finer produce than any one

of between twenty and thirty established varieties."

Andrew Knight[289] believed that his seedlings from crossed varieties

of the apple exhibited increased vigour and luxuriance; and M.

Chevreul[290] alludes to the extreme vigour of some of the crossed

fruit-trees raised by Sageret.

By crossing reciprocally the tallest and shortest peas, Knight[291]

says, "I had in this experiment a striking instance of the stimulative

effects of crossing the breeds; for the smallest variety, whose height

rarely exceeded two feet, was increased to six feet; whilst the height

of the large and luxuriant kind was very little diminished." Mr. Laxton

gave me seed-peas produced from crosses between four distinct kinds;

and the plants thus raised were extraordinarily vigorous, being in each

case from one to two or three feet taller than the parent-forms growing

close alongside them.

{130}

Wiegmann[292] made many crosses between several varieties of cabbage;

and he speaks with astonishment of the vigour and height of the

mongrels, which excited the amazement of all the gardeners who beheld

them. Mr. Chaundy raised a great number of mongrels by planting

together six distinct varieties of cabbage. These mongrels displayed an

infinite diversity of character; "But the most remarkable circumstance

was, that, while all the other cabbages and borecoles in the nursery

were destroyed by a severe winter, these hybrids were little injured,

and supplied the kitchen when there was no other cabbage to be had."

Mr. Maund exhibited before the Royal Agricultural Society[293]

specimens of crossed wheat, together with their parent varieties; and

the editor states that they were intermediate in character, "united

with that greater vigour of growth, which it appears, in the vegetable

as in the animal world, is the result of a first cross." Knight also

crossed several varieties of wheat,[294] and he says "that in the years

1795 and 1796, when almost the whole crop of corn in the island was

blighted, the varieties thus obtained, and these only, escaped in this

neighbourhood, though sown in several different soils and situations."

Here is a remarkable case: M. Clotzsch[295] crossed _Pinus sylvestris_

and _nigricans_, _Quercus robur_ and _pedunculata, Alnus glutinosa_ and

_incana_, _Ulmus campestris_ and _effusa_; and the cross-fertilised

seeds, as well as seeds of the pure parent-trees, were all sown at the

same time and in the same place. The result was, that after an interval

of eight years, the hybrids were one-third taller than the pure trees!

* * * * *

The facts above given refer to undoubted varieties, excepting the trees

crossed by Clotzsch, which are ranked by various botanists as

strongly-marked races, sub-species, or species. That true hybrids

raised from entirely distinct species, though they lose in fertility,

often gain in size and constitutional vigour, is certain. It would be

superfluous to quote any facts; for all experimenters, Koelreuter,

Gaertner, Herbert, Sageret, Lecoq, and Naudin, have been struck with

the wonderful vigour, height, size, tenacity of life, precocity, and

hardiness of their hybrid productions. Gaertner[296] sums up his

conviction on this head in the strongest terms. Koelreuter[297] gives

numerous precise measurements of the weight and height of his hybrids

in comparison with measurements of both parent-forms; and speaks with

astonishment of their "_statura portentosa_," their "_ambitus

vastissimus ac altitudo valde conspicua_." Some exceptions to the rule

in the case of very sterile hybrids have, however, been noticed by

Gaertner and {131} Herbert; but the most striking exceptions are given

by Max Wichura,[298] who found that hybrid willows were generally

tender in constitution, dwarf, and short-lived.

Koelreuter explains the vast increase in the size of the roots, stems,

&c., of his hybrids, as the result of a sort of compensation due to

their sterility, in the same way as many emasculated animals are larger

than the perfect males. This view seems at first sight extremely

probable, and has been accepted by various authors;[299] but

Gaertner[300] has well remarked that there is much difficulty in fully

admitting it; for with many hybrids there is no parallelism between the

degree of their sterility and their increased size and vigour. The most

striking instances of luxuriant growth have been observed with hybrids

which were not sterile in any extreme degree. In the genus Mirabilis,

certain hybrids are unusually fertile, and their extraordinary

luxuriance of growth, together with their enormous roots,[301] have

been transmitted to their progeny. The increased size of the hybrids

produced between the fowl and pheasant, and between the distinct

species of pheasants, has been already noticed. The result in all cases

is probably in part due to the saving of nutriment and vital force

through the sexual organs not acting, or acting imperfectly, but more

especially to the general law of good being derived from a cross. For

it deserves especial attention that mongrel animals and plants, which

are so far from being sterile that their fertility is often actually

augmented, have, as previously shown, their size, hardiness, and

constitutional vigour generally increased. It is not a little

remarkable that an accession of vigour and size should thus arise under

the opposite contingencies of increased and diminished fertility.

It is a perfectly well ascertained fact[302] that hybrids will

invariably breed more readily with either pure parent, and not rarely

with a distinct species, than with each other. Herbert is inclined to

explain even this fact by the advantage derived from a cross; but

Gaertner more justly accounts for it by the pollen of the hybrid, and

probably its ovules, being in some degree vitiated, whereas the pollen

and ovules of both pure parents and of any third species are sound.

Nevertheless there are some well-ascertained and remarkable facts,

which, as we shall immediately see, show that the act of crossing in

itself undoubtedly tends to increase or re-establish the fertility of

hybrids.

_On certain Hermaphrodite Plants which, either normally or abnormally,

require to be fertilised by pollen from a distinct individual or species._

The facts now to be given differ from those hitherto detailed, as the

self-sterility does not here result from long-continued, {132} close

interbreeding. These facts are, however, connected with our present

subject, because a cross with a distinct individual is shown to be either

necessary or advantageous. Dimorphic and trimorphic plants, though they are

hermaphrodites, must be reciprocally crossed, one set of forms by the

other, in order to be fully fertile, and in some cases to be fertile in any

degree. But I should not have noticed these plants, had it not been for the

following cases given by Dr. Hildebrand:[303]--

_Primula sinensis_ is a reciprocally dimorphic species: Dr. Hildebrand

fertilised twenty-eight flowers of both forms, each by pollen of the

other form, and obtained the full number of capsules containing on an

average 42.7 seed per capsule; here we have complete and normal

fertility. He then fertilised forty-two flowers of both forms with

pollen of the same form, but taken from a distinct plant, and all

produced capsules containing on an average only 19.6 seed. Lastly, and

here we come to our more immediate point, he fertilised forty-eight

flowers of both forms with pollen of the same form, taken from the same

flower, and now he obtained only thirty-two capsules, and these

contained on an average 18.6 seed, or one less per capsule than in the

former case. So that, with these illegitimate unions, the act of

impregnation is less assured, and the fertility slightly less, when the

pollen and ovules belong to the same flower, than when belonging to two

distinct individuals of the same form. Dr. Hildebrand has recently made

analogous experiments on the long-styled form of _Oxalis rosea_, with

the same result.[304]

It has recently been discovered that certain plants, whilst growing in

their native country under natural conditions, cannot be fertilised with

pollen from the same plant. They are sometimes so utterly self-impotent,

that, though they can readily be fertilised by the pollen of a distinct

species or even distinct genus, yet, wonderful as the fact is, they never

produce a single seed by their own pollen. In some cases, moreover, the

plant's own pollen and stigma mutually act on each other in a deleterious

manner. Most of the facts to be given relate to Orchids, but I will

commence with a plant belonging to a widely different family.

Sixty-three flowers of _Corydalis cava_, borne on distinct plants, were

fertilised by Dr. Hildebrand[305] with pollen from other plants of the

same species; and fifty-eight capsules were obtained, including on an

average {133} 4.5 seed in each. He then fertilised sixteen flowers

produced by the same raceme, one with another, but obtained only three

capsules, one of which alone contained any good seeds, namely, two in

number. Lastly, he fertilised twenty-seven flowers, each with its own

pollen; he left also fifty-seven flowers to be spontaneously

fertilised, and this would certainly have ensued if it had been

possible, for the anthers not only touch the stigma, but the

pollen-tubes were seen by Dr. Hildebrand to penetrate it; nevertheless

these eighty-four flowers did not produce a single seed-capsule! This

whole case is highly instructive, as it shows how widely different the

action of the same pollen is, according as it is placed on the stigma

of the same flower, or on that of another flower on the same raceme, or

on that of a distinct plant.

With exotic Orchids several analogous cases have been observed, chiefly

by Mr. John Scott.[306] _Oncidium sphacelatum_ has effective pollen,

for with it Mr. Scott fertilised two distinct species; its ovules are

likewise capable of impregnation, for they were readily fertilised by

the pollen of _O. divaricatum_; nevertheless, between one and two

hundred flowers fertilised by their own pollen did not produce a single

capsule, though the stigmas were penetrated by the pollen-tubes. Mr.

Robinson Munro, of the Royal Botanic Gardens of Edinburgh, also informs

me (1864) that a hundred and twenty flowers of this same species were

fertilised by him with their own pollen, and did not produce a capsule,

but eight flowers fertilised by the pollen of _O. divaricatum_ produced

four fine capsules: again, between two and three hundred flowers of _O.

divaricatum_, fertilised by their own pollen, did not set a capsule,

but twelve flowers fertilised by _O. flexuosum_ produced eight fine

capsules: so that here we have three utterly self-impotent species,

with their male and female organs perfect, as shown by their mutual

fertilisation. In these cases fertilisation was effected only by the

aid of a distinct species. But, as we shall presently see, distinct

plants, raised from seed, of _Oncidium flexuosum_, and probably of the

other species, would have been perfectly capable of fertilising each

other, for this is the natural process. Again, Mr. Scott found that the

pollen of a plant of _O. microchilum_ was good, for with it he

fertilised two distinct species; he found its ovules good, for they

could be fertilised by the pollen of one of these species, and by the

pollen of a distinct plant of _O. microchilum_; but they could not be

fertilised by pollen of the same plant, though the pollen-tubes

penetrated the stigma. An analogous case has been recorded by M.

Riviere,[307] with two plants of _O. Cavendishianum_, which were both

self-sterile, but reciprocally fertilised each other. All these cases

refer to the genus Oncidium, but Mr. Scott found that _Maxillaria

atro-rubens_ was "totally insusceptible of fertilisation with its own

pollen," but fertilised, and was fertilised by, a widely distinct

species, viz. _M. squalens_.

As these orchids had grown under unnatural conditions, in {134}

hot-houses, I concluded without hesitation that their self-sterility

was due to this cause. But Fritz Mueller informs me that at Desterro,

in Brazil, he fertilised above one hundred flowers of the

above-mentioned _Oncidium flexuosum_, which is there endemic, with its

own pollen, and with that taken from distinct plants; all the former

were sterile, whilst those fertilised by pollen from any _other plant_

of the same species were fertile. During the first three days there was

no difference in the action of the two kinds of pollen: that placed on

the stigma of the same plant separated in the usual manner into grains,

and emitted tubes which penetrated the column, and the stigmatic

chamber shut itself; but the flowers alone which had been fertilised by

pollen taken from a distinct plant produced seed-capsules. On a

subsequent occasion these experiments were repeated on a large scale

with the same result. Fritz Mueller found that four other endemic

species of Oncidium were in like manner utterly sterile with their own

pollen, but fertile with that from any other plant: some of them

likewise produced seed-capsules when impregnated with pollen of widely

distinct genera, such as Leptotes, Cyrtopodium, and Rodriguezia!

_Oncidium crispum_, however, differs from the foregoing species in

varying much in its self-sterility; some plants producing fine pods

with their own pollen, others failing to do so; in two or three

instances, Fritz Mueller observed that the pods produced by pollen

taken from a distinct flower on the same plant, were larger than those

produced by the flower's own pollen. In _Epidendrum cinnabarinum_, an

orchid belonging to another division of the family, fine pods were

produced by the plant's own pollen, but they contained by weight only

about half as much seed as the capsules which had been fertilized by

pollen from a distinct plant, and in one instance from a distinct

species; moreover, a very large proportion, and in some cases nearly

all the seed produced by the plant's own pollen, was embryonless and

worthless. Some self-fertilized capsules of a Maxillaria were in a

similar state.

Another observation made by Fritz Mueller is highly remarkable, namely,

that with various orchids the plant's own pollen not only fails to

impregnate the flower, but acts on the stigma, and is acted on, in an

injurious or poisonous manner. This is shown by the surface of the

stigma in contact with the pollen, and by the pollen itself, becoming

in from three to five days dark brown, and then decaying. The

discolouration and decay are not caused by parasitic cryptogams, which

were observed by Fritz Mueller in only a single instance. These changes

are well shown by placing on the same stigma, at the same time, the

plant's own pollen and that from a distinct plant of the same species,

or of another species, or even of another and widely remote genus.

Thus, on the stigma of _Oncidium flexuosum_, the plant's own pollen and

that from a distinct plant were placed side by side, and in five days'

time the latter was perfectly fresh, whilst the plant's own pollen was

brown. On the other hand, when the pollen of a distinct plant of the

_Oncidium flexuosum_, and of the _Epidendrum zebra_ (_nov. spec.?_),

were placed together on the same stigma, they behaved in exactly the

same manner, the grains separating, emitting tubes, and penetrating the

stigma, so that the two {135} pollen-masses, after an interval of

eleven days, could not be distinguished except by the difference of

their caudicles, which, of course, undergo no change. Fritz Mueller

has, moreover, made a large number of crosses between orchids belonging

to distinct species and genera, and he finds that in all cases when the

flowers are not fertilised their footstalks first begin to wither; and

the withering slowly spreads upwards until the germens fall off, after

an interval of one or two weeks, and in one instance of between six and

seven weeks; but even in this latter case, and in most other cases, the

pollen and stigma remained in appearance fresh. Occasionally, however,

the pollen becomes brownish, generally on the external surface, and not

in contact with the stigma, as is invariably the case when the plant's

own pollen is applied.

Fritz Mueller observed the poisonous action of the plant's own pollen

in the above-mentioned _Oncidium flexuosum_, _O. unicorne, pubes_

(_?_), and in two other unnamed species. Also in two species of

Rodriguezia, in two of Notylia, in one of Burlingtonia, and of a fourth

genus in the same group. In all these cases, except the last, it was

proved that the flowers were, as might have been expected, fertile with

pollen from a distinct plant of the same species. Numerous flowers of

one species of Notylia were fertilized with pollen from the same

raceme; in two days' time they all withered, the germens began to

shrink, the pollen-masses became dark brown, and not one pollen-grain

emitted a tube. So that in this orchid the injurious action of the

plant's own pollen is more rapid than with _Oncidium flexuosum_. Eight

other flowers on the same raceme were fertilized with pollen from a

distinct plant of the same species: two of these were dissected, and

their stigmas were found to be penetrated by numberless pollen-tubes;

and the germens of the other six flowers became well developed. On a

subsequent occasion many other flowers were fertilized with their own

pollen, and all fell off dead in a few days; whilst some flowers on the

same raceme which had been left simply unfertilised adhered and long

remained fresh. We have seen that in cross-unions between extremely

distinct orchids the pollen long remains undecayed; but Notylia behaved

in this respect differently; for when its pollen was placed on the

stigma of _Oncidium flexuosum_, both the stigma and pollen quickly

became dark brown, in the same manner as if the plant's own pollen had

been applied.

Fritz Mueller suggests that, as in all these cases the plant's own

pollen is not only impotent (thus effectually preventing

self-fertilization), but likewise prevents, as was ascertained in the

case of the Notylia and _Oncidium flexuosum_, the action of

subsequently applied pollen from a distinct individual, it would be an

advantage to the plant to have its own pollen rendered more and more

deleterious; for the germens would thus quickly be killed, and,

dropping off, there would be no further waste in nourishing a part

which ultimately could be of no avail. Fritz Mueller's discovery that a

plant's own pollen and stigma in some cases act on each other as if

mutually poisonous, is certainly most remarkable.

We now come to cases closely analogous with those just {136} given, but

different, inasmuch as individual plants alone of the species are

self-impotent. This self-impotence does not depend on the pollen or ovules

being in a state unfit for fertilisation, for both have been found

effective in union with other plants of the same or of a distinct species.

The fact of these plants having spontaneously acquired so peculiar a

constitution, that they can be fertilised more readily by the pollen of a

distinct species than by their own, is remarkable. These abnormal cases, as

well as the foregoing normal cases, in which certain orchids, for instance,

can be much more easily fertilised by the pollen of a distinct species than

by their own, are exactly the reverse of what occurs with all ordinary

species. For in these latter the two sexual elements of the same individual

plant are capable of freely acting on each other; but are so constituted

that they are more or less impotent when brought into union with the sexual

elements of a distinct species, and produce more or less sterile hybrids.

It would appear that the pollen or ovules, or both, of the individual

plants which are in this abnormal state, have been affected in some strange

manner by the conditions to which they themselves or their parents have

been exposed; but whilst thus rendered self-sterile, they have retained the

capacity common to most species of partially fertilizing and being

partially fertilized by allied forms. However this may be, the subject, to

a certain extent, is related to our general conclusion that good is derived

from the act of crossing.

Gaertner experimented on two plants of _Lobelia fulgens_, brought from

separate places, and found[308] that their pollen was good, for he

fertilised with it _L. cardinalis_ and _syphilitica_; their ovules were

likewise good, for they were fertilised by the pollen of these same two

species; but these two plants of _L. fulgens_ could not be fertilised

by their own pollen, as can generally be effected with perfect ease

with this species. Again, the pollen of a plant of _Verbascum nigrum_

grown in a pot was found by Gaertner[309] capable of fertilising _V.

lychnitis_ and _V. Austriacum_; the ovules could be fertilised by the

pollen of _V. thapsus_; but the flowers could not be fertilised by

their own pollen. Koelreuter, also,[310] gives the case of three {137}

garden plants of _Verbascum phoeniceum_, which bore during two years

many flowers; these he successfully fertilised by the pollen of no less

than four distinct species, but they produced not a seed with their own

apparently good pollen; subsequently these same plants, and others

raised from seed, assumed a strangely fluctuating condition, being

temporarily sterile on the male or female side, or on both sides, and

sometimes fertile on both sides; but two of the plants were perfectly

fertile throughout the summer.

It appears[311] that certain flowers on certain plants of _Lilium

candidum_ can be fertilised more easily by pollen from a distinct

individual than by their own. So, again, with the varieties of the

potato. Tinzmann,[312] who made many trials with this plant, says that

pollen from another variety sometimes "exerts a powerful influence, and

I have found sorts of potatoes which would not bear seed from

impregnation with the pollen of their own flowers, would bear it when

impregnated with other pollen." It does not, however, appear to have

been proved that the pollen which failed to act on the flower's own

stigma was in itself good.

In the genus Passiflora it has long been known that several species do

not produce fruit, unless fertilised by pollen taken from distinct

species: thus, Mr. Mowbray[313] found that he could not get fruit from

_P. alata_ and _racemosa_ except by reciprocally fertilising them with

each other's pollen. Similar facts have been observed in Germany and

France;[314] and I have received two authentic accounts of _P.

quadrangularis_, which never produced fruit with its own pollen, but

would do so freely when fertilised in one case with the pollen of _P.

coerulea_, and in another case with that of _P. edulis_. So again, with

respect to _P. laurifolia_, a cultivator of much experience has

recently remarked[315] that the flowers "must be fertilised with the

pollen of _P. coerulea_, or of some other common kind, as their own

pollen will not fertilise them." But the fullest details on this

subject have been given by Mr. Scott:[316] plants of _Passiflora

racemosa_, _coerulea_, and _alata_ flowered profusely during many years

in the Botanic Gardens of Edinburgh, and, though repeatedly fertilised

by Mr. Scott and by others with their own pollen, never produced any

seed; yet this occurred at once with all three species when they were

crossed together in various ways. But in the case of _P. coerulea_,

three plants, two of which grew in the Botanic Gardens, were all

rendered fertile, merely by impregnating the one with pollen of the

other. The same result was attained in the same manner with _P. alata_,

but only with one plant out of three. As so many self-sterile species

have been mentioned, it may be stated that in the case of _P.

gracilis_, which is an annual, the flowers are nearly as fertile with

their own pollen as with that from a distinct plant; thus sixteen

flowers {138} spontaneously self-fertilised produced fruit, each

containing on an average 21.3 seed, whilst fruit from fourteen crossed

flowers contained 24.1 seed.

Returning to _P. alata_, I have received (1866) some interesting

details from Mr. Robinson Munro. Three plants, including one in

England, have already been mentioned which were inveterately

self-sterile, and Mr. Munro informs me of several others which, after

repeated trials during many years, have been found in the same

predicament. At some other places, however, this species fruits readily

when fertilised with its own pollen. At Taymouth Castle there is a

plant which was formerly grafted by Mr. Donaldson on a distinct

species, name unknown, and ever since the operation it has produced

fruit in abundance by its own pollen; so that this small and unnatural

change in the state of this plant has restored its self-fertility! Some

of the seedlings from the Taymouth Castle plant were found to be not

only sterile with their own pollen, but with each other's pollen, and

with the pollen of distinct species. Pollen from the Taymouth plant

failed to fertilise certain plants of the same species, but was

successful on one plant in the Edinburgh Botanic Gardens. Seedlings

were raised from this latter union, and some of their flowers were

fertilised by Mr. Munro with their own pollen; but they were found to

be as self-impotent as the mother-plant had always proved, except when

fertilised by the grafted Taymouth plant, and except, as we shall see,

when fertilised by her own seedlings. For Mr. Munro fertilised eighteen

flowers on the self-impotent mother-plant with pollen from these her

own self-impotent seedlings, and obtained, remarkable as the fact is,

eighteen fine capsules full of excellent seed! I have met with no case

in regard to plants which shows so well as this of _P. alata_, on what

small and mysterious causes complete fertility or complete sterility

depends.

The facts hitherto given relate to the much-lessened or completely

destroyed fertility of pure species when impregnated with their own pollen,

in comparison with their fertility when impregnated by distinct individuals

or distinct species; but closely analogous facts have been observed with

hybrids.

Herbert states[317] that having in flower at the same time nine hybrid

Hippeastrums, of complicated origin, descended from several species, he

found that "almost every flower touched with pollen from another cross

produced seed abundantly, and those which were touched with their own

pollen either failed entirely, or formed slowly a pod of inferior size,

with fewer seeds." In the 'Horticultural Journal' he adds that, "the

admission of the pollen of another cross-bred Hippeastrum (however

complicated the cross) to any _one_ flower of the number, is almost

sure to check the fructification of the others." In a letter written to

me in 1839, Dr. Herbert says that he had already tried these

experiments during five consecutive years, and he subsequently repeated

them, with the same invariable result. {139} He was thus led to make an

analogous trial on a pure species, namely, on the _Hippeastrum

aulicum_, which he had lately imported from Brazil: this bulb produced

four flowers, three of which were fertilised by their own pollen, and

the fourth by the pollen of a triple cross between _H. bulbulosum_,

_reginae_, and _vittatum_; the result was, that "the ovaries of the

three first flowers soon ceased to grow, and after a few days perished

entirely: whereas the pod impregnated by the hybrid made vigorous and

rapid progress to maturity, and bore good seed, which vegetated

freely." This is, indeed, as Herbert remarks, "a strange truth," but

not so strange as it then appeared.

As a confirmation of these statements, I may add that Mr. M.

Mayes,[318] after much experience in crossing the species of Amaryllis

(Hippeastrum), says, "neither the species nor the hybrids will, we are

well aware, produce seed so abundantly from their own pollen as from

that of others." So, again, Mr. Bidwell, in New South Wales,[319]

asserts that _Amaryllis belladonna_ bears many more seeds when

fertilised by the pollen of _Brunswigia_ (_Amaryllis_ of some authors)

_Josephinae_ or of _B. multiflora_, than when fertilised by its own

pollen. Mr. Beaton dusted four flowers of a Cyrtanthus with their own

pollen, and four with the pollen of _Vallota_ (_Amaryllis_) _purpurea_;

on the seventh day "those which received their own pollen slackened

their growth, and ultimately perished; those which were crossed with

the Vallota held on."[320] These latter cases, however, relate to

uncrossed species, like those before given with respect to Passiflora,

Orchids, &c., and are here referred to only because the plants belong

to the same group of Amaryllidaceae.

In the experiments on the hybrid Hippeastrums, if Herbert had found

that the pollen of two or three kinds alone had been more efficient on

certain kinds than their own pollen, it might have been argued that

these, from their mixed parentage, had a closer mutual affinity than

the others; but this explanation is inadmissible, for the trials were

made reciprocally backwards and forwards on nine different hybrids; and

a cross, whichever way taken, always proved highly beneficial. I can

add a striking and analogous case from experiments made by the Rev. A.

Rawson, of Bromley Common, with some complex hybrids of Gladiolus. This

skilful horticulturist possessed a number of French varieties,

differing from each other only in the colour and size of the flowers,

all descended from Gandavensis, a well-known old hybrid, said to be

descended from _G. Natalensis_ by the pollen of _G.

oppositiflorus_.[321] Mr. Rawson, after repeated trials, found that

none of the varieties would set seed with their own pollen, although

{140} taken from distinct plants of the same variety, which had, of

course, been propagated by bulbs, but that they all seeded freely with

pollen from any other variety. To give two examples: Ophir did not

produce a capsule with its own pollen, but when fertilised with that of

Janire, Brenchleyensis, Vulcain, and Linne, it produced ten fine

capsules; but the pollen of Ophir was good, for when Linne was

fertilised by it seven capsules were produced. This later variety, on

the other hand, was utterly barren with its own pollen, which we have

seen was perfectly efficient on Ophir. Altogether, Mr. Rawson, in the

year 1861, fertilised twenty-six flowers borne by four varieties with

pollen taken from other varieties, and every single flower produced a

fine seed-capsule; whereas fifty-two flowers on the same plants,

fertilised at the same time with their own pollen, did not yield a

single seed-capsule. Mr. Rawson fertilised, in some cases, the

alternate flowers, and in other cases all those down one side of the

spike, with pollen of other varieties, and the remaining flowers with

their own pollen; I saw these plants when the capsules were nearly

mature, and their curious arrangement at once brought full conviction

to the mind that an immense advantage had been derived from crossing

these hybrids.

Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made

numerous experiments in crossing the species of Cistus, but as not yet

published the results, that, when any of these hybrids are fertile,

they may be said to be, in regard to function, dioecious; "for the

flowers are always sterile when the pistil is fertilised by pollen

taken from the same flower or from flowers on the same plant. But they

are often fertile if pollen be employed from a distinct individual of

the same hybrid nature, or from a hybrid made by a reciprocal cross."

_Conclusion._--The facts just given, which show that certain plants are

self-sterile, although both sexual elements are in a fit state for

reproduction when united with distinct individuals of the same or other

species, appear at first sight opposed to all analogy. The sexual elements

of the same flower have become, as already remarked, differentiated in

relation to each other, almost like those of two distinct species.

With respect to the species which, whilst living under their natural

conditions, have their reproductive organs in this peculiar state, we may

conclude that it has been naturally acquired for the sake of effectually

preventing self-fertilisation. The case is closely analous with dimorphic

and trimorphic plants, which can be fully fertilised only by plants belong

to the opposite form, and not, as in the foregoing cases, in differently by

any other plant. Some of these dimorphic plants are completely sterile with

pollen taken from the same plant or from the same {141} form. It is

interesting to observe the graduated series from plants which, when

fertilised by their own pollen, yield the full number of seed, but with the

seedlings a little dwarfed in stature--to plants which when self-fertilised

yield few seeds--to those with yield none--and, lastly, to those in which

the plant's own pollen and stigma act on each other like poison. This

peculiar state of the reproductive organs, when occurring in certain

individuals alone, is evidently abnormal; and as it chiefly affects exotic

plants, or indigenous plants cultivated in pots, we may attribute it to

some change in the conditions of life, acting on the plants themselves or

on their parents. The self-impotent _Passiflora alata_, which recovered its

self-fertility after having been grafted on a distinct stock, shows how

small a change is sufficient to act powerfully on the reproductive system.

The possibility of a plant becoming under culture self-impotent is

interesting as throwing light on the occurrence of this same condition in

natural species. A cultivated plant in this state generally remains so

during its whole life; and from this fact we may infer that the state is

probably congenital.

Koelreuter, however, has described some plants of Verbascum which varied in

this respect even during the same season. As in all the normal cases, and

in many, probably in most, of the abnormal cases, any two self-impotent

plants can reciprocally fertilize each other, we may infer that a very

slight difference in the nature of their sexual elements suffices to give

fertility; but in other instances, as with some Passifloras and the hybrid

Gladioli, a greater degree of differentiation appears to be necessary, for

with these plants fertility is gained only by the union of distinct

species, or of hybrids of distinct parentage. These facts all point to the

same general conclusion, namely, that good is derived from a cross between

individuals, which either innately, or from exposure to dissimilar

conditions, have come to differ in sexual constitution.

Exotic animals confined in menageries are sometimes in nearly the same

state as the above-described self-impotent plants; for, as we shall see in

the following chapter, certain monkeys, the larger carnivora, several

finches, geese, and pheasants, cross together, quite as freely as, or even

more freely than, the individuals of the same species breed together. Cases

will, {142} also, be given of sexual incompatibility between certain male

and female domesticated animals, which, nevertheless, are fertile when

matched with any other individual of the same kind.

In the early part of this chapter it was shown that the crossing of

distinct forms, whether closely or distantly allied, gives increased size

and constitutional vigour, and, except in the case of crossed species,

increased fertility, to the offspring. The evidence rests on the universal

testimony of breeders (for it should be observed that I am not here

speaking of the evil results of close interbreeding), and is practically

exemplified in the higher value of cross-bred animals for immediate

consumption. The good results of crossing have also been demonstrated, in

the case of some animals and of numerous plants, by actual weight and

measurement. Although animals of pure blood will obviously be deteriorated

by crossing, as far as their characteristic qualities are concerned, there

seems to be no exception to the rule that advantages of the kind just

mentioned are thus gained, even when there has not been any previous close

interbreeding. The rule applies to all animals, even to cattle and sheep,

which can long resist breeding in-and-in between the nearest

blood-relations. It applies to individuals of the same sub-variety but of

distinct families, to varieties or races, to sub-species, as well as to

quite distinct species.

In this latter case, however, whilst size, vigour, precocity, and hardiness

are, with rare exceptions, gained, fertility, in a greater or less degree,

is lost; but the gain cannot be exclusively attributed to the principle of

compensation; for there is no close parallelism between the increased size

and vigour of the offspring and their sterility. Moreover it has been

clearly proved that mongrels which are perfectly fertile gain these same

advantages as well as sterile hybrids.

The evil consequences of long-continued close interbreeding are not so

easily recognised as the good effects from crossing, for the deterioration

is gradual. Nevertheless it is the general opinion of those who have had

most experience, especially with animals which propagate quickly, that evil

does inevitably follow sooner or later, but at different rates with

different animals. No doubt a false belief may widely prevail like a

superstition; yet it is difficult to suppose that so many acute and

original {143} observers have all been deceived at the expense of much cost

and trouble. A male animal may sometimes be paired with his daughter,

granddaughter, and so on, even for seven generations, without any manifest

bad result; but the experiment has never been tried of matching brothers

and sisters, which is considered the closest form of interbreeding, for an

equal number of generations. There is good reason to believe that by

keeping the members of the same family in distinct bodies, especially if

exposed to somewhat different conditions of life, and by occasionally

crossing these families, the evil results may be much diminished, or quite

eliminated. These results are loss of constitutional vigour, size, and

fertility; but there is no necessary deterioration in the general form of

the body, or in other good qualities. We have seen that with pigs

first-rate animals have been produced after long-continued close

interbreeding, though they had become extremely infertile when paired with

their near relations. The loss of fertility, when it occurs, seems never to

be absolute, but only relative to animals of the same blood; so that this

sterility is to a certain extent analogous with that of self-impotent

plants which cannot be fertilised by their own pollen, but are perfectly

fertile with pollen of any other plant of the same species. The fact of

infertility of this peculiar nature being one of the results of

long-continued interbreeding, shows that interbreeding does not act merely

by combining and augmenting various morbid tendencies common to both

parents; for animals with such tendencies, if not at the time actually ill,

can generally propagate their kind. Although offspring descended from the

nearest blood-relations are not necessarily deteriorated in structure, yet

some authors[322] believe that they are eminently liable to malformations;

and this is not improbable, as everything which lessens the vital powers

acts in this manner. Instances of this kind have been recorded in the case

of pigs, bloodhounds, and some other animals.

Finally, when we consider the various facts now given which plainly show

that good follows from crossing, and less plainly {144} that evil follows

from close interbreeding, and when we bear in mind that throughout the

whole organic world elaborate provision has been made for the occasional

union of distinct individuals, the existence of a great law of nature is,

if not proved, at least rendered in the highest degree probable; namely,

that the crossing of animals and plants which are not closely related to

beach other is highly beneficial or even necessary, and that interbreeding

prolonged during many generations is highly injurious.

* * * * *

{145}

CHAPTER XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE:

STERILITY FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF

LIFE--STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE

COUNTRY AND IN MENAGERIES--MAMMALS, BIRDS, AND INSECTS--LOSS OF

SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS--CAUSES OF

STERILITY--STERILITY OF DOMESTICATED ANIMALS FROM CHANGED

CONDITIONS--SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS--STERILITY OF

PLANTS FROM CHANGED CONDITIONS OF LIFE--CONTABESCENCE OF THE

ANTHERS--MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE

FLOWERS--SEEDLESS FRUIT--STERILITY FROM THE EXCESSIVE DEVELOPMENT OF

THE ORGANS OF VEGETATION--FROM LONG-CONTINUED PROPAGATION BY

BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND

SEEDLESS FRUIT.

_On the Good derived from slight Changes in the Conditions of Life._--In

considering whether any facts were known which might throw light on the

conclusion arrived at in the last chapter, namely, that benefits ensue from

crossing, and that it is a law of nature that all organic beings should

occasionally cross, it appeared to me probable that the good derived from

slight changes in the conditions of life, from being an analogous

phenomenon, might serve this purpose. No two individuals, and still less no

two varieties, are absolutely alike in constitution and structure; and when

the germ of one is fertilised by the male element of another, we may

believe that it is acted on in a somewhat similar manner as an individual

when exposed to slightly changed conditions. Now, every one must have

observed the remarkable influence on convalescents of a change of

residence, and no medical man doubts the truth of this fact. Small farmers

who hold but little land are convinced that their cattle derive great

benefit from a change of pasture. In the case of plants, the evidence is

strong that a great advantage is derived from exchanging seeds, tubers,

bulbs, and cuttings from one soil or place to another as different as

possible. {146}

The belief that plants are thus benefited, whether or not well founded,

has been firmly maintained from the time of Columella, who wrote

shortly after the Christian era, to the present day; and it now

prevails in England, France, and Germany.[323] A sagacious observer,

Bradley, writing in 1724,[324] says, "When we once become Masters of a

good Sort of Seed, we should at least put it into Two or Three Hands,

where the Soils and Situations are as different as possible; and every

Year the Parties should change with one another; by which Means, I find

the Goodness of the Seed will be maintained for several Years. For Want

of this Use many Farmers have failed in their Crops and been great

Losers." He then gives his own practical experience on this head. A

modern writer[325] asserts, "Nothing can be more clearly established in

agriculture than that the continual growth of any one variety in the

same district makes it liable to deterioration either in quality or

quantity." Another writer states that he sowed close together in the

same field two lots of wheat-seed, the product of the same original

stock, one of which had been grown on the same land, and the other at a

distance, and the difference in favour of the crop from the latter seed

was remarkable. A gentleman in Surrey who has long made it his business

to raise wheat to sell for seed, and who has constantly realised in the

market higher prices than others, assures me that he finds it

indispensable continually to change his seed; and that for this purpose

he keeps two farms differing much in soil and elevation.

With respect to the tubers of the potato, I find that at the present

day the practice of exchanging sets is almost everywhere followed. The

great growers of potatoes in Lancashire formerly used to get tubers

from Scotland, but they found that "a change from the moss-lands, and

_vice versa_, was generally sufficient." In former times in France the

crop of potatoes in the Vosges had become reduced in the course of

fifty or sixty years in the proportion from 120-150 to 30-40 bushels;

and the famous Oberlin attributed the surprising good which he effected

in large part to changing the sets.[326]

A well-known practical gardener, Mr. Robson[327] positively states that

he has himself witnessed decided advantage from obtaining bulbs of the

onion, tubers of the potato, and various seeds, all of the same kind,

from different soils and distant parts of England. He further states

that with {147} plants propagated by cuttings, as with the Pelargonium,

and especially the Dahlia, manifest advantage is derived from getting

plans of the same variety, which have been cultivated in another place;

or, "where the extent of the place allows, to take cuttings from one

description of soil to plant on another, so as to afford the change

that seems so necessary to the well-being of the plants." He maintains

that after a time an exchange of this nature is "forced on the grower,

whether he be prepared for it or not." Similar remarks have been made

by another excellent gardener, Mr. Fish, namely, that cuttings of the

same variety of Calceolaria, which he obtained from a neighbour,

"showed much greater vigour than some of his own that were treated in

exactly the same manner," and he attributed this solely to his own

plants having become "to a certain extent worn out or tired of their

quarters." Something of this kind apparently occurs in grafting and

budding fruit-trees; for, according to Mr. Abbey, grafts or buds

generally take on a distinct variety or even species, or on a stock

previously grafted, with greater facility than on stocks raised from

seeds of the variety which is to be grafted; and he believes this

cannot be altogether explained by the stocks in question being better

adapted to the soil and climate of the place. It should, however, be

added, that varieties grafted or budded on very distinct kinds, though

they may take more readily and grow at first more vigorously than when

grafted on closely allied stocks, afterwards often become unhealthy.

I have studied M. Tessier's careful and elaborate experiments,[328]

made to disprove the common belief that good is derived from a change

of seed; and he certainly shows that the same seed may with care be

cultivated on the same farm (it is not stated whether on exactly the

same soil) for ten consecutive years without loss. Another excellent

observer, Colonel Le Couteur,[329] has come to the same conclusion; but

then he expressly adds, if the same seed be used, "that which is grown

on land manured from the mixen one year becomes seed for land prepared

with lime, and that again becomes seed for land dressed with ashes,

then for land dressed with mixed manure, and so on." But this in effect

is a systematic exchange of seed, within the limits of the same farm.

On the whole the belief, which has long been held by many skilful

cultivators, that good follows from exchanging seed, tubers, &c., seems to

be fairly well founded. Considering the small size of most seeds, it seems

hardly credible that the advantage thus derived can be due to the seeds

obtaining in one soil some chemical element deficient in the other soil. As

plants after once germinating naturally become fixed to the same spot, it

might have been anticipated that they would show the good effects of a

change more plainly than animals, which continually wander about; and this

apparently is the {148} case. Life depending on, or consisting in, an

incessant play of the most complex forces, it would appear that their

action is in some way stimulated by slight changes in the circumstances to

which each organism is exposed. All forces throughout nature, as Mr.

Herbert Spencer[330] remarks, tend towards an equilibrium, and for the life

of each being it is necessary that this tendency should be checked. If

these views and the foregoing facts can be trusted, they probably throw

light, on the one hand, on the good effects of crossing the breed, for the

germ will be thus slightly modified or acted on by new forces; and on the

other hand, on the evil effects of close interbreeding prolonged during

many generations, during which the germ will be acted on by a male having

almost identically the same constitution.

_Sterility from changed Conditions of Life._

I will now attempt to show that animals and plants, when removed from their

natural conditions, are often rendered in some degree infertile or

completely barren; and this occurs even when the conditions have not been

greatly changed. This conclusion is not necessarily opposed to that at

which we have just arrived, namely, that lesser changes of other kinds are

advantageous to organic beings. Our present subject is of some importance,

from having an intimate connexion with the causes of variability.

Indirectly it perhaps bears on the sterility of species when crossed: for

as, on the one hand, slight changes in the conditions of life are

favourable to plants and animals, and the crossing of varieties adds to the

size, vigour, and fertility of their offspring; so, on the other hand,

certain other changes in the conditions of life cause sterility; and as

this likewise ensues from crossing much-modified forms or species, we have

a parallel and double series of facts, which apparently stand in close

relation to each other.

It is notorious that many animals, though perfectly tamed, {149} refuse to

breed in captivity. Isidore Geoffroy St. Hilaire[331] consequently has

drawn a broad distinction between tamed animals which will not breed under

captivity, and truly domesticated animals which breed freely--generally

more freely, as shown in the sixteenth chapter, than in a state of nature.

It is possible and generally easy to tame most animals; but experience has

shown that it is difficult to get them to breed regularly, or even at all.

I shall discuss this subject in detail; but will give only those cases

which seem most illustrative. My materials are derived from notices

scattered through various works, and especially from a Report, drawn up for

me by the kindness of the officers of the Zoological Society of London,

which has especial value, as it records all the cases, during nine years

from 1838-46, in which the animals were seen to couple but produced no

offspring, as well as the cases in which they never, as far as known,

coupled. This MS. Report I have corrected by the annual Reports

subsequently published. Many facts are given on the breeding of the animals

in that magnificent work, 'Gleanings from the Menageries of Knowsley Hall,'

by Dr. Gray. I made, also, particular inquiries from the experienced keeper

of the birds in the old Surrey Zoological Gardens. I should premise that a

slight change in the treatment of animals sometimes makes a great

difference in their fertility; and it is probable that the results observed

in different menageries would differ. Indeed some animals in our Zoological

Gardens have become more productive since the year 1846. It is, also,

manifest from F. Cuvier's account of the Jardin des Plantes,[332] that the

animals formerly bred much less freely there than with us; for instance, in

the Duck tribe, which is highly prolific, only one species had at that

period produced young.

The most remarkable cases, however, are afforded by animals kept in

their native country, which, though perfectly tamed, quite healthy, and

allowed some freedom, are absolutely incapable of breeding.

Rengger,[333] who in Paraguay particularly attended to this subject,

specifies six quadrupeds in this condition; and he mentions two or

three others which most rarely {150} breed. Mr. Bates, in his admirable

work on the Amazons, strongly insists on similar cases;[334] and he

remarks, that the fact of thoroughly tamed native mammals and birds not

breeding when kept by the Indians, cannot be wholly accounted for by

their negligence or indifference, for the turkey is valued by them, and

the fowl has been adopted by the remotest tribes. In almost every part

of the world--for instance, in the interior of Africa, and in several

of the Polynesian islands--the natives are extremely fond of taming the

indigenous quadrupeds and birds; but they rarely or never succeed in

getting them to breed.

The most notorious case of an animal not breeding in captivity is that

of the elephant. Elephants are kept in large numbers in their native

Indian home, live to old age, and are vigorous enough for the severest

labour; yet, with one or two exceptions, they have never been known

even to couple, though both males and females have their proper

periodical seasons. If, however, we proceed a little eastward to Ava,

we hear from Mr. Crawfurd[335] that their "breeding in the domestic

state, or at least in the half-domestic state in which the female

elephants are generally kept, is of every-day occurrence;" and Mr.

Crawfurd informs me that he believes that the difference must be

attributed solely to the females being allowed to roam the forests with

some degree of freedom. The captive rhinoceros, on the other hand,

seems from Bishop Heber's account[336] to breed in India far more

readily than the elephant. Four wild species of the horse genus have

bred in Europe, though here exposed to a great change in their natural

habits of life; but the species have generally been crossed one with

another. Most of the members of the pig family breed readily in our

menageries: even the Red River hog (_Potamochoerus penicillatus_), from

the sweltering plains of West Africa, has bred twice in the Zoological

Gardens. Here also the Peccary (_Dicotyles torquatus_) has bred several

times; but another species, the _D. labiatus_, though rendered so tame

as to be half-domesticated, breeds so rarely in its native country of

Paraguay, that according to Rengger[337] the fact requires

confirmation. Mr. Bates remarks that the tapir, though often kept tame

in Amazonia by the Indians, never breeds.

Ruminants generally breed quite freely in England, though brought from

widely different climates, as may be seen in the Annual Reports of the

Zoological Gardens, and in the Gleanings from Lord Derby's menagerie.

The Carnivora, with the exception of the Plantigrade division,

generally breed (though with capricious exceptions) almost as freely as

ruminants. Many species of Felidae have bred in various menageries,

although imported from various climates and closely confined. Mr.

Bartlett, the present superintendent of the Zoological Gardens,[338]

remarks that the lion appears to breed more frequently and to bring

forth more young at a birth than any other species of the family. He

adds that the tiger has rarely bred; {151} "but there are several

well-authenticated instances of the female tiger breeding with the

lion." Strange as the fact may appear, many animals under confinement

unite with distinct species and produce hybrids quite as freely as, or

even more freely than, with their own species. On inquiring from Dr.

Falconer and others, it appears that the tiger when confined in India

does not breed, though it has been known to couple. The cheetah (_Felis

jubata_) has never been known by Mr. Bartlett to breed in England, but

it has bred at Frankfort; nor does it breed in India, where it is kept

in large numbers for hunting; but no pains would be taken to make them

breed, as only those animals which have hunted for themselves in a

state of nature are serviceable and worth training.[339] According to

Rengger, two species of wild cats in Paraguay, though thoroughly tamed,

have never bred. Although so many of the Felidae breed readily in the

Zoological Gardens, yet conception by no means always follows union: in

the nine-year Report, various species are specified which were observed

to couple seventy-three times, and no doubt this must have passed many

times unnoticed; yet from the seventy-three unions only fifteen births

ensued. The Carnivora in the Zoological Gardens were formerly less

freely exposed to the air and cold than at present, and this change of

treatment, as I was assured by the former superintendent, Mr. Miller,

greatly increased their fertility. Mr. Bartlett, and there cannot be a

more capable judge, says, "it is remarkable that lions breed more

freely in travelling collections than in the Zoological Gardens;

probably the constant excitement and irritation produced by moving from

place to place, or change of air, may have considerable influence in

the matter."

Many members of the Dog family breed readily when confined. The Dhole

is one of the most untameable animals in India, yet a pair kept there

by Dr. Falconer produced young. Foxes, on the other hand, rarely breed,

and I have never heard of such an occurrence with the European fox: the

silver fox of North America (_Canis argentatus_), however, has bred

several times in the Zoological Gardens. Even the otter has bred there.

Every one knows how readily the semi-domesticated ferret breeds, though

shut up in miserably small cages; but other species of Viverra and

Paradoxurus absolutely refuse to breed in the Zoological Gardens. The

Genetta has bred both here and in the Jardin des Plantes, and produced

hybrids. The _Herpestes fasciatus_ has likewise bred; but I was

formerly assured that the _H. griseus_, though many were kept in the

Gardens, never bred.

The Plantigrade Carnivora breed under confinement much less freely,

without our being able to assign any reason, than other members of the

group. In the nine-year Report it is stated that the bears had been

seen in the Zoological Gardens to couple freely, but previously to 1848

had most rarely conceived. In the Reports published since this date

three species have produced young (hybrids in one case), and, wonderful

to relate, the white Polar bear has produced young. The badger (_Meles

taxus_) has bred several times in the Gardens; but I have not heard of

this {152} occurring elsewhere in England, and the event must be very

rare, for an instance in Germany has been thought worth recording.[340]

In Paraguay the native Nasua, though kept in pairs during many years

and perfectly tamed, has never been known, according to Rengger, to

breed or show any sexual passion; nor, as I hear from Mr. Bates, does

this animal, or the Cercoleptes, breed in the region of the Amazons.

Two other plantigrade genera, Procyon and Gulo, though often kept tame

in Paraguay, never breed there. In the Zoological Gardens species of

Nasua and Procyon have been seen to couple; but they did not produce

young.

As domesticated rabbits, guinea-pigs, and white mice breed so

abundantly when closely confined under various climates, it might have

been thought that most other members of the Rodent order would have

bred in captivity, but this is not the case. It deserves notice, as

showing how the capacity to breed sometimes goes by affinity, that the

one native rodent of Paraguay, which there breeds _freely_ and has

yielded successive generations, is the _Cavia aperea_; and this animal

is so closely allied to the guinea-pig, that it has been erroneously

thought to be the parent-form.[341] In the Zoological Gardens, some

rodents have coupled, but have never produced young; some have neither

coupled nor bred; but a few have bred, as the porcupine more than once,

the Barbary mouse, lemming, chinchilla, and the agouti (_Dasyprocta

aguti_), several times. This latter animal has also produced young in

Paraguay, though they were born dead and ill-formed; but in Amazonia,

according to Mr. Bates, it never breeds, though often kept tame about

the houses. Nor does the paca (_Coelogenys paca_) breed there. The

common hare when confined has, I believe, never bred in Europe;[342]

though, according to a recent statement, it has crossed with the

rabbit. I have never heard of the dormouse breeding in confinement. But

squirrels offer a more curious case: with one exception, no species has

ever bred in the Zoological Gardens, yet as many as fourteen

individuals of _S. palmarum_ were kept together during several years.

The _S. cinerea_ has been seen to couple, but it did not produce young;

nor has this species, when rendered extremely tame in its native

country, North America, been ever known to breed.[343] At Lord Derby's

menagerie squirrels of many kinds were kept in numbers, but Mr.

Thompson, the superintendent, told me that none had ever bred there, or

elsewhere as far as he knew. I have never heard of the English squirrel

breeding in confinement. But the species which has bred more than once

in the Zoological Gardens is the one which perhaps might have been

least expected, namely, the flying squirrel (_Sciuropterus volucella_):

it has, also, bred several times {153} near Birmingham; but the female

never produced more than two young at a birth, whereas in its native

American home she bears from three to six young.[344]

Monkeys, in the nine-year Report from the Zoological Gardens, are

stated to unite most freely, but during this period, though many

individuals were kept, there were only seven births. I have heard of

one American monkey alone, the Ouistiti, breeding in Europe.[345] A

Macacus, according to Flourens, bred in Paris; and more than one

species of this genus has produced young in London, especially the

_Macacus rhesus_, which everywhere shows a special capacity to breed

under confinement. Hybrids have been produced both in Paris and London

from this same genus. The Arabian baboon, or _Cynocephalus

hamadryas_,[346] and a Cercopithecus have bred in the Zoological

Gardens, and the latter species at the Duke of Northumberland's.

Several members of the family of Lemurs have produced hybrids in the

Zoological Gardens. It is much more remarkable that monkeys very rarely

breed when confined in their native country; thus the Cay (_Cebus

azarae_) is frequently and completely tamed in Paraguay, but

Rengger[347] says that it breeds so rarely, that he never saw more than

two females which had produced young. A similar observation has been

made with respect to the monkeys which are frequently tamed by the

aborigines in Brazil.[348] In the region of the Amazons, these animals

are so often kept in a tame state, that Mr. Bates in walking through

the streets of Para counted thirteen species; but, as he asserts, they

have never been known to breed in captivity.[349]

_Birds._

Birds offer in some respects better evidence than quadrupeds, from

their breeding more rapidly and being kept in greater numbers. We have

seen that carnivorous animals are more fertile under confinement than

most other mammals. The reverse holds good with carnivorous birds. It

is said[350] that as many as eighteen species have been used in Europe

for hawking, and several others in Persia and India;[351] they have

been kept in their native country in the finest condition, and have

been flown during six, eight, or nine years;[352] yet there is no

record of their having ever produced young. As these birds were

formerly caught whilst young, at great expense, being imported from

Iceland, Norway, and Sweden, there can {154} be little doubt that, if

possible, they would have been propagated. In the Jardin des Plantes,

no bird of prey has been known to couple.[353] No hawk, vulture, or owl

has ever produced fertile eggs in the Zoological Gardens, or in the old

Surrey Gardens, with the exception, in the former place on one

occasion, of a condor and a kite (_Milvus niger_). Yet several species,

namely, the _Aquila fusca_, _Haliaetus leucocephalus_, _Falco

tinnunculus_, _F. subbuteo_, and _Buteo vulgaris_, have been seen to

couple in the Zoological Gardens. Mr. Morris[354] mentions as a unique

fact that a kestrel (_Falco tinnunculus_) bred in an aviary. The one

kind of owl which has been known to couple in the Zoological Gardens

was the Eagle Owl (_Bubo maximus_); and this species shows a special

inclination to breed in captivity; for a pair at Arundel Castle, kept

more nearly in a state of nature "than ever fell to the lot of an

animal deprived of its liberty,"[355] actually reared their young. Mr.

Gurney has given another instance of this same owl breeding in

confinement; and he records the case of a second species of owl, the

_Strix passerina_, breeding in captivity.[356]

Of the smaller graminivorous birds, many kinds have been kept tame in

their native countries, and have lived long; yet, as the highest

authority on cage-birds[357] remarks, their propagation is "uncommonly

difficult." The canary-bird shows that there is no inherent difficulty

in these birds breeding freely in confinement; and Audubon says[358]

that the _Fringilla_ (_Spiza_) _ciris_ of North America breeds as

perfectly as the canary. The difficulty with the many finches which

have been kept in confinement is all the more remarkable as more than a

dozen species could be named which have yielded hybrids with the

canary; but hardly any of these, with the exception of the siskin

(_Fringilla spinus_), have reproduced their own kind. Even the

bullfinch (_Loxia pyrrhula_) has bred as frequently with the canary,

though belonging to a distinct genus, as with its own species.[359]

With respect to the skylark (_Alauda arvensis_), I have heard of birds

living for seven years in an aviary, which never produced young; and a

great London bird-fancier assured me that he had never known an

instance of their breeding; nevertheless one case has been

recorded.[360] In the nine-year Report from the Zoological Society,

twenty-four incessorial species are enumerated which had not bred, and

of these only four were known to have coupled.

Parrots are singularly long-lived birds; and Humboldt mentions the

curious fact of a parrot in South America, which spoke the language of

{155} an extinct Indian tribe, so that this bird preserved the sole

relic of a lost language. Even in this country there is reason to

believe[361] that parrots have lived to the age of nearly one hundred

years; yet, though many have been kept in Europe, they breed so rarely

that the event has been thought worth recording in the gravest

publications.[362] According to Bechstein[363] the African _Psittacus

erithacus_ breeds oftener than any other species: the _P. macoa_

occasionally lays fertile eggs, but rarely succeeds in hatching them;

this bird, however, has the instinct of incubation sometimes so

strongly developed, that it will hatch the eggs of fowls or pigeons. In

the Zoological Gardens and in the old Surrey Gardens some few species

have coupled, but, with the exception of three species of parrakeets,

none have bred. It is a much more remarkable fact that in Guiana

parrots of two kinds, as I am informed by Sir E. Schomburgk, are often

taken from the nests by the Indians and reared in large numbers; they

are so tame that they fly freely about the houses, and come when called

to be fed, like pigeons; yet he has never heard of a single instance of

their breeding.[364] In Jamaica, a resident naturalist, Mr. R.

Hill,[365] says, "no birds more readily submit to human dependence than

the parrot-tribe, but no instance of a parrot breeding in this tame

life has been known yet." Mr. Hill specifies a number of other native

birds kept tame in the West Indies, which never breed in this state.

The great pigeon family offers a striking contrast with parrots: in the

nine-year Report thirteen species are recorded as having bred, and,

what is more noticeable, only two were seen to couple without any

result. Since the above date every annual Report gives many cases of

various pigeons breeding. The two magnificent crowned pigeons (_Goura

coronata_ and _Victoriae_) produced hybrids; nevertheless, of the

former species more than a dozen birds were kept, as I am informed by

Mr. Crawfurd, in a park at Penang, under a perfectly well-adapted

climate, but never once bred. The _Columba migratoria_ in its native

country, North America, invariably lays two eggs, but in Lord Derby's

menagerie never more than one. The same fact has been observed with the

_C. leucocephala_.[366]

Gallinaceous birds of many genera likewise show an eminent capacity for

breeding under captivity. This is particularly the case with pheasants;

yet our English species seldom lays more than ten eggs in confinement;

whilst from eighteen to twenty is the usual number in the wild

state.[367] With the Gallinaceae, as with all other orders, there are

marked and {156} inexplicable exceptions in regard to the fertility of

certain species and genera under confinement. Although many trials have

been made with the common partridge, it has rarely bred, even when

reared in large aviaries; and the hen will never hatch her own

eggs.[368] The American tribe of Guans or Cracidae are tamed with

remarkable ease, but are very shy breeders in this country;[369] but

with care various species were formerly made to breed rather freely in

Holland.[370] Birds of this tribe are often kept in a perfectly tamed

condition in their native country by the Indians, but they never

breed.[371] It might have been expected that grouse from their habits

of life would not have bred in captivity, more especially as they are

said soon to languish and die.[372] But many cases are recorded of

their breeding: the capercailzie (_Tetrao urogallus_) has bred in the

Zoological Gardens; it breeds without much difficulty when confined in

Norway, and in Russia five successive generations have been reared:

_Tetrao tetrix_ has likewise bred in Norway; _T. Scoticus_ in Ireland;

_T. umbellus_ at Lord Derby's; and _T. cupido_ in North America.

It is scarcely possible to imagine a greater change in habits than that

which the members of the ostrich family must suffer, when cooped up in

small enclosures under a temperate climate, after freely roaming over

desert and tropical plains or entangled forests. Yet almost all the

kinds, even the mooruk (_Casuarius Bennettii_) from New Ireland, has

frequently produced young in the various European menageries. The

African ostrich, though perfectly healthy and living long in the South

of France, never lays more than from twelve to fifteen eggs, though in

its native country it lays from twenty-five to thirty.[373] Here we

have another instance of fertility impaired, but not lost, under

confinement, as with the flying squirrel, the hen-pheasant, and two

species of American pigeons.

Most Waders can be tamed, as the Rev. E. S. Dixon informs me, with

remarkable facility; but several of them are short-lived under

confinement, so that their sterility in this state is not surprising.

The cranes breed more readily than other genera: _Grus montigresia_ has

bred several times in Paris and in the Zoological Gardens, as has _G.

cinerea_ at the latter place, and _G. antigone_ at Calcutta. Of other

members of this great order, _Tetrapteryx paradisea_ has bred at

Knowsley, a Porphyrio in Sicily, and the _Gallinula chloropus_ in the

Zoological Gardens. On the other hand, several {157} birds belonging to

this order will not breed in their native country, Jamaica; and the

Psophia, though often kept by the Indians of Guiana about their houses,

"is seldom or never known to breed."[374]

No birds breed with such complete facility under confinement as the

members of the great Duck family; yet, considering their aquatic and

wandering habits, and the nature of their food, this could not have

been anticipated. Even some time ago above two dozen species had bred

in the Zoological Gardens; and M. Selys-Longchamps has recorded the

production of hybrids from forty-four different members of the family;

and to these Professor Newton has added a few more cases.[375] "There

is not," says Mr. Dixon,[376] "in the wide world, a goose which is not

in the strict sense of the word domesticable;" that is, capable of

breeding under confinement; but this statement is probably too bold.

The capacity to breed sometimes varies in individuals of the same

species; thus Audubon[377] kept for more than eight years some wild

geese (_Anser Canadensis_), but they would not mate; whilst other

individuals of the same species produced young during the second year.

I know of but one instance in the whole family of a species which

absolutely refuses to breed in captivity, namely, the _Dendrocygna

viduata_, although, according to Sir R. Schomburgk,[378] it is easily

tamed, and is frequently kept by the Indians of Guiana. Lastly, with

respect to Gulls, though many have been kept in the Zoological Gardens

and in the old Surrey Gardens, no instance was known before the year

1848 of their coupling or breeding; but since that period the herring

gull (_Larus argentatus_) has bred many times in the Zoological Gardens

and at Knowsley.

There is reason to believe that insects are affected by confinement

like the higher animals. It is well known that the Sphingidae rarely

breed when thus treated. An entomologist[379] in Paris kept twenty-five

specimens of _Saturnia pyri_, but did not succeed in getting a single

fertile egg. A number of females of _Orthosia munda_ and of _Mamestra

suasa_ reared in confinement were unattractive to the males.[380] Mr.

Newport kept nearly a hundred individuals of two species of Vanessa,

but not one paired; this, however, might have been due to their habit

of coupling on the wing.[381] Mr. Atkinson could never succeed in India

in making the Tarroo silk-moth breed in confinement.[382] It appears

that a number of moths, especially the Sphingidae, when hatched in the

autumn out of their proper season, {158} are completely barren; but

this latter case is still involved in some obscurity.[383]

Independently of the fact of many animals under confinement not coupling,

or, if they couple, not producing young, there is evidence of another kind,

that their sexual functions are thus disturbed. For many cases have been

recorded of the loss by male birds when confined of their characteristic

plumage. Thus the common linnet (_Linota cannabina_) when caged does not

acquire the fine crimson colour on its breast, and one of the buntings

(_Emberiza passerina_) loses the black on its head. A Pyrrhula and an

Oriolus have been observed to assume the quiet plumage of the hen-bird; and

the _Falco albidus_ returned to the dress of an earlier age.[384] Mr.

Thomson, the superintendent of the Knowsley menagerie, informed me that he

had often observed analogous facts. The horns of a male deer (_Cervus

Canadensis_) during the voyage from America were badly developed; but

subsequently in Paris perfect horns were produced.

When conception takes place under confinement, the young are often born

dead, or die soon, or are ill-formed. This frequently occurs in the

Zoological Gardens, and, according to Rengger, with native animals confined

in Paraguay. The mother's milk often fails. We may also attribute to the

disturbance of the sexual functions the frequent occurrence of that

monstrous instinct which leads the mother to devour her own offspring,--a

mysterious case of perversion, as it at first appears.

Sufficient evidence has now been advanced to prove that animals when first

confined are eminently liable to suffer in their reproductive systems. We

feel at first naturally inclined to attribute the result to loss of health,

or at least to loss of vigour; but this view can hardly be admitted when we

reflect how healthy, long-lived, and vigorous many animals are under {159}

captivity, such as parrots, and hawks when used for hawking, chetahs when

used for hunting, and elephants. The reproductive organs themselves are not

diseased; and the diseases, from which animals in menageries usually

perish, are not those which in any way affect their fertility. No domestic

animal is more subject too disease than the sheep, yet it is remarkably

prolific. The failure of animals to breed under confinement has been

sometimes attributed exclusively to a failure in their sexual instincts:

this may occasionally come into play, but there is no obvious reason why

this instinct should be especially liable to be affected with perfectly

tamed animals, except indeed indirectly through the reproductive system

itself being disturbed. Moreover, numerous cases have been given of various

animals which couple freely under confinement, but never conceive; or, if

they conceive and produce young, these are fewer in number than is natural

to the species. In the vegetable kingdom instinct of course can play no

part; and we shall presently see that plants when removed from their

natural conditions are affected in nearly the same manner as animals.

Change of climate cannot be the cause of the loss of fertility, for, whilst

many animals imported into Europe from extremely different climates breed

freely, many others when confined in their native land are completely

sterile. Change of food cannot be the chief cause; for ostriches, ducks,

and many other animals, which must have undergone a great change in this

respect, breed freely. Carnivorous birds when confined are extremely

sterile; whilst most carnivorous mammals, except plantigrades, are

moderately fertile. Nor can the amount of food be the cause; for a

sufficient supply will certainly be given to valuable animals; and there is

no reason to suppose that much more food would be given to them, than to

our choice domestic productions which retain their full fertility. Lastly,

we may infer from the case of the elephant, chetah, various hawks, and of

many animals which are allowed to lead an almost free life in their native

land, that want of exercise is not the sole cause.