SELECTION, continued.
NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS.
CHARACTERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE.
CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN.
FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE CONDITIONS.
CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE.
THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE.
WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED.
HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION.
TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT,
LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE.
CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE
ALREADY VARIED.
DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, LEADS
TO DISTINCTNESS IN OUR DOMESTIC RACES.
LIMIT TO THE POWER OF SELECTION.
LAPSE OF TIME IMPORTANT.
MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED.
SUMMARY.
NATURAL SELECTION, OR THE SURVIVAL OF THE FITTEST, AS AFFECTING DOMESTIC
PRODUCTIONS.
We know little on this head. But as animals kept by savages have to provide
throughout the year their own food either entirely or to a large extent, it
can hardly be doubted that in different countries, varieties differing in
constitution and in various characters would succeed best, and so be naturally
selected. Hence perhaps it is that the few domesticated animals kept by
savages partake, as has been remarked by more than one writer, of the wild
appearance of their masters, and likewise resemble natural species. Even in
long-civilised countries, at least in the wilder parts, natural selection must
act on our domestic races. It is obvious that varieties having very different
habits, constitution, and structure, would succeed best on mountains and on
rich lowland pastures. For example, the improved Leicester sheep were formerly
taken to the Lammermuir Hills; but an intelligent sheep-master reported that
"our coarse lean pastures were unequal to the task of supporting such heavy-
bodied sheep; and they gradually dwindled away into less and less bulk: each
generation was inferior to the preceding one; and when the spring was severe,
seldom more than two-thirds of the lambs survived the ravages of the storms."
(21/1. Quoted by Youatt on 'Sheep' page 325. See also Youatt on 'Cattle' pages
62, 69.) So with the mountain cattle of North Wales and the Hebrides, it has
been found that they could not withstand being crossed with the larger and
more delicate lowland breeds. Two French naturalists, in describing the horses
of Circassia, remark that, subjected as they are to extreme vicissitudes of
climate, having to search for scanty pasture, and exposed to constant danger
from wolves, the strongest and most vigorous alone survive. (21/2. MM.
Lherbette and De Quatrefages in 'Bull. Soc. d'Acclimat.' tome 8 1861 page
311.)
Every one must have been struck with the surpassing grace, strength, and
vigour of the Game-cock, with its bold and confident air, its long, yet firm
neck, compact body, powerful and closely pressed wings, muscular thighs,
strong beak massive at the base, dense and sharp spurs set low on the legs for
delivering the fatal blow, and its compact, glossy, and mail-like plumage
serving as a defence. Now the English game-cock has not only been improved
during many years by man's careful selection, but in addition, as Mr.
Tegetmeier has remarked (21/3. 'The Poultry Book' 1866 page 123. Mr.
Tegetmeier, 'The Homing or Carrier Pigeon' 1871 pages 45-58.), by a kind of
natural selection, for the strongest, most active and courageous birds have
stricken down their antagonists in the cockpit, generation after generation,
and have subsequently served as the progenitors of their race. The same kind
of double selection has come into play with the carrier pigeon, for during
their training the inferior birds fail to return home and are lost, so that
even without selection by man only the superior birds propagate their race.
In Great Britain, in former times, almost every district had its own breed of
cattle and sheep; "they were indigenous to the soil, climate, and pasturage of
the locality on which they grazed: they seemed to have been formed for it and
by it." (21/4. 'Youatt on Sheep' page 312.) But in this case we are quite
unable to disentangle the effects of the direct action of the conditions of
life,--of use or habit--of natural selection--and of that kind of selection
which we have seen is occasionally and unconsciously followed by man even
during the rudest periods of history.
Let us now look to the action of natural selection on special characters.
Although nature is difficult to resist, yet man often strives against her
power, and sometimes with success. From the facts to be given, it will also be
seen that natural selection would powerfully affect many of our domestic
productions if left unprotected. This is a point of much interest, for we thus
learn that differences apparently of very slight importance would certainly
determine the survival of a form when forced to struggle for its own
existence. It may have occurred to some naturalists, as it formerly did to me,
that, though selection acting under natural conditions would determine the
structure of all important organs, yet that it could not affect characters
which are esteemed by us of little importance; but this is an error to which
we are eminently liable, from our ignorance of what characters are of real
value to each living creature.
When man attempts to make a breed with some serious defect in structure, or in
the mutual relation of the several parts, he will partly or completely fail,
or encounter much difficulty; he is in fact resisted by a form of natural
selection. We have seen that an attempt was once made in Yorkshire to breed
cattle with enormous buttocks, but the cows perished so often in bringing
forth their calves, that the attempt had to be given up. In rearing short-
faced tumblers, Mr. Eaton says (21/5. 'Treatise on the Almond Tumbler' 1851
page 33.), "I am convinced that better head and beak birds have perished in
the shell than ever were hatched; the reason being that the amazingly short-
faced bird cannot reach and break the shell with its beak, and so perishes."
Here is a more curious case, in which natural selection comes into play only
at long intervals of time: during ordinary seasons the Niata cattle can graze
as well as others, but occasionally, as from 1827 to 1830 the plains of La
Plata suffer from long-continued droughts and the pasture is burnt up; at such
times common cattle and horses perish by the thousand, but many survive by
browsing on twigs, reeds, etc.; this the Niata cattle cannot so well effect
from their upturned jaws and the shape of their lips; consequently, if not
attended to, they perish before the other cattle. In Columbia, according to
Roulin, there is a breed of nearly hairless cattle, called Pelones; these
succeed in their native hot district, but are found too tender for the
Cordillera; in this case, however, natural selection determines only the range
of the variety. It is obvious that a host of artificial races could never
survive in a state of nature;--such as Italian greyhounds,--hairless and
almost toothless Turkish dogs,--fantail pigeons, which cannot fly well against
a strong wind,--barbs and Polish fowls, with their vision impeded by their eye
wattles and great topknots,--hornless bulls and rams, which consequently
cannot cope with other males, and thus have a poor chance of leaving
offspring,--seedless plants, and many other such cases.
Colour is generally esteemed by the systematic naturalist as unimportant: let
us, therefore, see how far it indirectly affects our domestic productions, and
how far it would affect them if they were left exposed to the full force of
natural selection. In a future chapter I shall have to show that
constitutional peculiarities of the strangest kind, entailing liability to the
action of certain poisons, are correlated with the colour of the skin. I will
here give a single case, on the high authority of Professor Wyman; he informs
me that, being surprised at all the pigs in a part of Virginia being black, he
made inquiries, and ascertained that these animals feed on the roots of the
Lachnanthes tinctoria, which colours their bones pink, and, excepting in the
case of the black varieties, causes the hoofs to drop off. Hence, as one of
the squatters remarked, "we select the black members of the litter for
raising, as they alone have a good chance of living." So that here we have
artificial and natural selection working hand in hand. I may add that in the
Tarentino the inhabitants keep black sheep alone, because the Hypericum
crispum abounds there; and this plant does not injure black sheep, but kills
the white ones in about a fortnight's time. (21/6. Dr. Heusinger
'Wochenschrift fur die Hei1kunde' Berlin 1846 s. 279.)
Complexion, and liability to certain diseases, are believed to run together in
man and the lower animals. Thus white terriers suffer more than those of any
other colour from the fatal distemper. (21/7. Youatt on the 'Dog' page 232.)
In North America plum-trees are liable to a disease which Downing (21/8. 'The
Fruit-trees of America' 1845 page 270: for peaches page 466.) believes is not
caused by insects; the kinds bearing purple fruit are most affected, "and we
have never known the green or yellow fruited varieties infected until the
other sorts had first become filled with the knots." On the other hand,
peaches in North America suffer much from a disease called the "yellows,"
which seems to be peculiar to that continent, and more than nine-tenths of the
victims, "when the disease first appeared, were the yellow-fleshed peaches.
The white-fleshed kinds are much more rarely attacked; in some parts of the
country never." In Mauritius, the white sugar-canes have of late years been so
severely attacked by a disease, that many planters have been compelled to give
up growing this variety (although fresh plants were imported from China for
trial), and cultivate only red canes. (21/9. 'Proc. Royal Soc. of Arts and
Sciences of Mauritius' 1852 page 135.) Now, if these plants had been forced to
struggle with other competing plants and enemies, there cannot be a doubt that
the colour of the flesh or skin of the fruit, unimportant as these characters
are considered, would have rigorously determined their existence.
Liability to the attacks of parasites is also connected with colour. White
chickens are certainly more subject than dark-coloured chickens to the
"gapes," which is caused by a parasitic worm in the trachea. (21/10.
'Gardener's Chronicle' 1856 page 379.) On the other hand, experience has shown
that in France the caterpillars which produce white cocoons resist the deadly
fungus better than those producing yellow cocoons. (21/11. Quatrefages
'Maladies Actuelles du Ver a Soie' 1859 pages 12, 214.) Analogous facts have
been observed with plants: a new and beautiful white onion, imported from
France, though planted close to other kinds, was alone attacked by a parasitic
fungus. (21/12. 'Gardener's Chronicle' 1851 page 595.) White verbenas are
especially liable to mildew. (21/13. 'Journal of Horticulture' 1862 page 476.)
Near Malaga, during an early period of the vine-disease, the green sorts
suffered most; "and red and black grapes, even when interwoven with the sick
plants, suffered not at all." In France whole groups of varieties were
comparatively free, and others, such as the Chasselas, did not afford a single
fortunate exception; but I do not know whether any correlation between colour
and liability to disease was here observed. (21/14. 'Gardener's Chronicle'
1852 pages 435, 691.) In a former chapter it was shown how curiously liable
one variety of the strawberry is to mildew.
It is certain that insects regulate in many cases the range and even the
existence of the higher animals, whilst living under their natural conditions.
Under domestication light-coloured animals suffer most: in Thuringia (21/15.
Bechstein 'Naturgesch. Deutschlands' 1801 b. 1 s. 310.) the inhabitants do not
like grey, white, or pale cattle, because they are much more troubled by
various kinds of flies than the brown, red, or black cattle. An Albino negro,
it has been remarked (21/16. Prichard 'Phys. Hist. of Mankind' 1851 volume 1
page 224.), was peculiarly sensitive to the bites of insects. In the West
Indies (21/17. G. Lewis 'Journal of Residence in West Indies' 'Home and Col.
Library' page 100.) it is said that "the only horned cattle fit for work are
those which have a good deal of black in them. The white are terribly
tormented by the insects; and they are weak and sluggish in proportion to the
white."
In Devonshire there is a prejudice against white pigs, because it is believed
that the sun blisters them when turned out (21/18. Sidney's edition of Youatt
on the 'Pig' page 24. I have given analogous facts in the case of mankind in
my 'Descent of Man' 2nd edition page 195.); and I knew a man who would not
keep white pigs in Kent, for the same reason. The scorching of flowers by the
sun seems likewise to depend much on colour; thus, dark pelargoniums suffer
most; and from various accounts it is clear that the cloth-of-gold variety
will not withstand a degree of exposure to sunshine which other varieties
enjoy. Another amateur asserts that not only all dark-coloured verbenas, but
likewise scarlets, suffer from the sun: "the paler kinds stand better, and
pale blue is perhaps the best of all." So again with the heartsease (Viola
tricolor); hot weather suits the blotched sorts, whilst it destroys the
beautiful markings of some other kinds. (21/19. 'Journal of Horticulture' 1862
pages 476, 498; 1865 page 460. With respect to the heartsease 'Gardener's
Chronicle' 1863 page 628.) During one extremely cold season in Holland all
red-flowered hyacinths were observed to be very inferior in quality. It is
believed by many agriculturists that red wheat is hardier in northern climates
than white wheat. (21/20. 'Des Jacinthes, de leur Culture' 1768 page 53: on
wheat 'Gardener's Chronicle' 1846 page 653.)
With animals, white varieties from being conspicuous are the most liable to be
attacked by beasts and birds of prey. In parts of France and Germany where
hawks abound, persons are advised not to keep white pigeons; for, as
Parmentier says, "it is certain that in a flock the white always first fall
victims to the kite." In Belgium, where so many societies have been
established for the flight of carrier-pigeons, white is the one colour which
for the same reason is disliked. (20/21. W.B. Tegetmeier 'The Field' February
25, 1865. With respect to black fowls see a quotation in Thompson 'Nat. Hist.
of Ireland' 1849 volume 1 page 22.) Prof. G. Jaeger (21/22. 'In Sachen
Darwin's contra Wigand' 1874 page 70.) whilst fishing found four pigeons which
had been killed by hawks, and all were white; on another occasion he examined
the eyrie of a hawk, and the feathers of the pigeons which had been caught
were all of a white or yellow colour. On the other hand, it is said that the
sea-eagle (Falco ossifragus, Linn.) on the west coast of Ireland picks out the
black fowls, so that "the villagers avoid as much as possible rearing birds of
that colour." M. Daudin (20/23. 'Bull. de la Soc. d'Acclimat.' tome 7 1860
page 359.), speaking of white rabbits kept in warrens in Russia, remarks that
their colour is a great disadvantage, as they are thus more exposed to attack,
and can be seen during bright nights from a distance. A gentleman in Kent, who
failed to stock his woods with a nearly white and hardy kind of rabbit,
accounted in the same manner for their early disappearance. Any one who will
watch a white cat prowling after her prey will soon perceive under what a
disadvantage she lies.
The white Tartarian cherry, "owing either to its colour being so much like
that of the leaves, or to the fruit always appearing from a distance unripe,"
is not so readily attacked by birds as other sorts. The yellow-fruited
raspberry, which generally comes nearly true by seed, "is very little molested
by birds, who evidently are not fond of it; so that nets may be dispensed with
in places where nothing else will protect the red fruit." (21/24. 'Transact.
Hort. Soc.' volume 1 2nd series 1835 page 275. For raspberries see 'Gardener's
Chronicle' 1855 page 154 and 1863 page 245.) This immunity, though a benefit
to the gardener, would be a disadvantage in a state of nature both to the
cherry and raspberry, as dissemination depends on birds. I noticed during
several winters that some trees of the yellow-berried holly, which were raised
from seed from a tree found wild by my father remained covered with fruit,
whilst not a scarlet berry could be seen on the adjoining trees of the common
kind. A friend informs me that a mountain-ash (Pyrus aucuparia) growing in his
garden bears berries which, though not differently coloured, are always
devoured by birds before those on the other trees. This variety of the
mountain-ash would thus be more freely disseminated, and the yellow-berried
variety of the holly less freely, than the common varieties of these two
trees.
Independently of colour, trifling differences are sometimes found to be of
importance to plants under cultivation, and would be of paramount importance
if they had to fight their own battle and to struggle with many competitors.
The thin-shelled peas, called pois sans parchemin, are attacked by birds
(21/25. 'Gardener's Chronicle' 1843 page 806.) much more commonly than
ordinary peas. On the other hand, the purple-podded pea, which has a hard
shell, escaped the attacks of tomtits (Parus major) in my garden far better
than any other kind. The thin-shelled walnut likewise suffers greatly from the
tomtit. (21/26. Ibid 1850 page 732.) These same birds have been observed to
pass over and thus favour the filbert, destroying only the other kinds of nuts
which grew in the same orchard. (21/27. Ibid 1860 page 956.)
Certain varieties of the pear have soft bark, and these suffer severely from
wood-boring beetles; whilst other varieties are known to resist their attacks
much better. (21/28. J. De Jonghe in 'Gardener's Chronicle' 1860 page 120.) In
North America the smoothness, or absence of down on the fruit, makes a great
difference in the attacks of the weevil, "which is the uncompromising foe of
all smooth stone-fruits;" and the cultivator "has the frequent mortification
of seeing nearly all, or indeed often the whole crop, fall from the trees when
half or two-thirds grown." Hence the nectarine suffers more than the peach. A
particular variety of the Morello cherry, raised in North America, is, without
any assignable cause, more liable to be injured by this same insect than other
cherry-trees. (21/29. Downing 'Fruit-trees of North America' pages 266, 501:
in regard to the cherry page 198.) From some unknown cause, certain varieties
of the apple enjoy, as we have seen, the great advantage in various parts of
the world of not being infested by the coccus. On the other hand, a particular
case has been recorded in which aphides confined themselves to the Winter
Nelis pear and touched no other kind in an extensive orchard. (21/30.
'Gardener's Chronicle' 1849 page 755.) The existence of minute glands on the
leaves of peaches, nectarines, and apricots, would not be esteemed by
botanists as a character of the least importance for they are present or
absent in closely-related sub-varieties, descended from the same parent-tree;
yet there is good evidence (21/31. 'Journal of Horticulture' September 26,
1865 page 254; see other references given in chapter 10.) that the absence of
glands leads to mildew, which is highly injurious to these trees.
A difference either in flavour or in the amount of nutriment in certain
varieties causes them to be more eagerly attacked by various enemies than
other varieties of the same species. Bullfinches (Pyrrhula vulgaris) injure
our fruit-trees by devouring the flower-buds, and a pair of these birds have
been seen "to denude a large plum-tree in a couple of days of almost every
bud;" but certain varieties (21/32. Mr. Selby in 'Mag. of Zoology and Botany'
Edinburgh volume 2 1838 page 393.) of the apple and thorn (Crataegus
oxyacantha) are more especially liable to be attacked. A striking instance of
this was observed in Mr. Rivers's garden, in which two rows of a particular
variety of plum (21/33. The Reine Claude de Bavay 'Journal of Horticulture'
December 27, 1864 page 511.) had to be carefully protected, as they were
usually stripped of all their buds during the winter, whilst other sorts
growing near them escaped. The root (or enlarged stem) of Laing's Swedish
turnip is preferred by hares, and therefore suffers more than other varieties.
Hares and rabbits eat down common rye before St. John's-day-rye, when both
grow together. (21/34. Mr. Pusey in 'Journal of R. Agricult. Soc.' volume 6
page 179. For Swedish turnips see 'Gardener's Chronicle' 1847 page 91.) In the
south of France, when an orchard of almond-trees is formed, the nuts of the
bitter variety are sown, "in order that they may not be devoured by field-
mice" (21/35. Godron 'De l'Espece' tome 2 page 98.); so we see the use of the
bitter principle in almonds.
Other slight differences, which would be thought quite unimportant, are no
doubt sometimes of great service both to plants and animals. The Whitesmith's
gooseberry, as formerly stated, produces its leaves later than other
varieties, and, as the flowers are thus left unprotected, the fruit often
fails. In one variety of the cherry, according to Mr. Rivers (21/36.
'Gardener's Chronicle' 1866 page 732.), the petals are much curled backwards,
and in consequence of this the stigmas were observed to be killed by a severe
frost; whilst at the same time, in another variety with incurved petals, the
stigmas were not in the least injured. The straw of the Fenton wheat is
remarkably unequal in height; and a competent observer believes that this
variety is highly productive, partly because the ears from being distributed
at various heights above the ground are less crowded together. The same
observer maintains that in the upright varieties the divergent awns are
serviceable by breaking the shocks when the ears are dashed together by the
wind. (21/37. 'Gardener's Chronicle' 1862 pages 820, 821.) If several
varieties of a plant are grown together, and the seed is indiscriminately
harvested, it is clear that the hardier and more productive kinds will, by a
sort of natural selection, gradually prevail over the others; this takes
place, as Colonel Le Couteur believes (21/38. 'On the Varieties of Wheat' page
59.), in our wheat-fields, for, as formerly shown, no variety is quite uniform
in character. The same thing, as I am assured by nurserymen, would take place
in our flower-gardens, if the seed of the different varieties were not
separately saved. When the eggs of the wild and tame duck are hatched
together, the young wild ducks almost invariably perish, from being of smaller
size and not getting their fair share of food. (21/39. Mr. Hewitt and others,
in 'Journal of Hort.' 1862 page 773.)
Facts in sufficient number have now been given showing that natural selection
often checks, but occasionally favours, man's power of selection. These facts
teach us, in addition, a valuable lesson, namely, that we ought to be
extremely cautious in judging what characters are of importance in a state of
nature to animals and plants, which have to struggle for existence from the
hour of their birth to that of their death,--their existence depending on
conditions, about which we are profoundly ignorant.
CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN.
The possibility of selection rests on variability, and this, as we shall see
in the following chapters, mainly depends on changed conditions of life, but
is governed by infinitely complex and unknown laws. Domestication, even when
long continued, occasionally causes but a small amount of variability, as in
the case of the goose and turkey. The slight differences, however, which
characterise each individual animal and plant would in most, probably in all,
cases suffice for the production of distinct races through careful and
prolonged selection. We see what selection, though acting on mere individual
differences, can effect when families of cattle, sheep, pigeons, etc., of the
same race, have been separately bred during a number of years by different men
without any wish on their part to modify the breed. We see the same fact in
the difference between hounds bred for hunting in different districts (21/40.
'Encyclop. of Rural Sports' page 405.), and in many other such cases.
In order that selection should produce any result, it is manifest that the
crossing of distinct races must be prevented; hence facility in pairing, as
with the pigeon, is highly favourable for the work; and difficulty in pairing,
as with cats, prevents the formation of distinct breeds. On nearly the same
principle the cattle of the small island of Jersey have been improved in their
milking qualities "with a rapidity that could not have been obtained in a
widely extended country like France." (21/41. Col. Le Couteur 'Journal Roy.
Agricult. Soc.' volume 4 page 43.) Although free crossing is a danger on the
one side which every one can see, too close interbreeding is a hidden danger
on the other side. Unfavourable conditions of life overrule the power of
selection. Our improved heavy breeds of cattle and sheep could not have been
formed on mountainous pastures; nor could dray-horses have been raised on a
barren and inhospitable land, such as the Falkland Islands, where even the
light horses of La Plata rapidly decrease in size. It seems impossible to
preserve several English breeds of sheep in France; for as soon as the lambs
are weaned their vigour decays as the heat of the summer increases (21/42.
Malingie-Nouel 'Journal R. Agricult. Soc.' volume 14 1853 pages 215, 217.): it
would be impossible to give great length of wool to sheep within the tropics;
yet selection has kept the Merino breed nearly true under diversified and
unfavourable conditions. The power of selection is so great, that breeds of
the dog, sheep, and poultry, of the largest and smallest size, long and short
beaked pigeons, and other breeds with opposite characters, have had their
characteristic qualities augmented, though treated in every way alike, being
exposed to the same climate and fed on the same food. Selection, however, is
either checked or favoured by the effects of use or habit. Our wonderfully-
improved pigs could never have been formed if they had been forced to search
for their own food; the English racehorse and greyhound could not have been
improved up to their present high standard of excellence without constant
training.
As conspicuous deviations of structure occur rarely, the improvement of each
breed is generally the result of the selection of slight individual
differences. Hence the closest attention, the sharpest powers of observation,
and indomitable perseverance, are indispensable. It is, also, highly important
that many individuals of the breed which is to be improved should be raised;
for thus there will be a better chance of the appearance of variations in the
right direction, and individuals varying in an unfavourable manner may be
freely rejected or destroyed. But that a large number of individuals should be
raised, it is necessary that the conditions of life should favour the
propagation of the species. Had the peacock been reared as easily as the fowl,
we should probably ere this have had many distinct races. We see the
importance of a large number of plants, from the fact of nursery gardeners
almost always beating amateurs in the exhibition of new varieties. In 1845 it
was estimated (21/43. Gardener's Chronicle' 1845 page 273.) that between 4000
and 5000 pelargoniums were annually raised from seed in England, yet a
decidedly improved variety is rarely obtained. At Messrs. Carter's grounds, in
Essex, where such flowers as the Lobelia, Nemophila, Mignonette, etc., are
grown by the acre for seed, "scarcely a season passes without some new kinds
being raised, or some improvement effected on old kinds." (21/44. 'Journal of
Horticulture' 1862 page 157.) At Kew, as Mr. Beaton remarks, where many
seedlings of common plants are raised, "you see new forms of Laburnums,
Spiraeas, and other shrubs." (21/45. 'Cottage Gardener' 1860 page 368.) So
with animals: Marshall (21/46. 'A Review of Reports' 1808 page 406.), in
speaking of the sheep in one part of Yorkshire, remarks, "as they belong to
poor people, and are mostly in small lots, they never can be improved." Lord
Rivers, when asked how he succeeded in always having first-rate greyhounds,
answered, "I breed many, and hang many." This, as another man remarks, "was
the secret of his success; and the same will be found in exhibiting fowls,--
successful competitors breed largely, and keep the best." (21/47. 'Gardener's
Chronicle' 1853 page 45.)
It follows from this that the capacity of breeding at an early age and at
short intervals, as with pigeons, rabbits, etc., facilitates selection; for
the result is thus soon made visible, and perseverance in the work encouraged.
It can hardly be an accident that the great majority of the culinary and
agricultural plants which have yielded numerous races are annuals or
biennials, which therefore are capable of rapid propagation, and thus of
improvement. Sea-kale, asparagus, common and Jerusalem artichokes, potatoes,
and onions, must be excepted, as they are perennials: but onions are
propagated like annuals, and of the other plants just specified, none, with
the exception of the potato, have yielded in this country more than one or two
varieties. In the Mediterranean region, where artichokes are often raised from
seed, there are several kinds, as I hear from Mr. Bentham. No doubt fruit-
trees, which cannot be propagated quickly by seed, have yielded a host of
varieties, though not permanent races; but these, judging from prehistoric
remains, have been produced at a comparatively late period.
A species may be highly variable, but distinct races will not be formed, if
from any cause selection be not applied. It would be difficult to select
slight variations in fishes from their place of habitation; and though the
carp is extremely variable and is much attended to in Germany, only one well-
marked race has been formed, as I hear from Lord A. Russell, namely the
spiegel-carpe; and this is carefully secluded from the common scaly kind. On
the other hand, a closely allied species, the gold-fish, from being reared in
small vessels, and from having been carefully attended to by the Chinese, has
yielded many races. Neither the bee, which has been semi-domesticated from an
extremely remote period, nor the cochineal insect, which was cultivated by the
aboriginal Mexicans (21/48. Isidore Geoffroy Saint-Hilaire 'Hist. Nat. Gen.'
tome 3 page 49. 'On the Cochineal Insect' page 46.), has yielded races; and it
would be impossible to match the queen-bee with any particular drone, and most
difficult to match cochineal insects. Silk-moths, on the other hand, have been
subjected to rigorous selection, and have produced a host of races. Cats,
which from their nocturnal habits cannot be selected for breeding, do not, as
formerly remarked, yield distinct races within the same country. Dogs are held
in abomination in the East, and their breeding is neglected; consequently, as
Prof. Moritz Wagner (21/49. 'Die Darwin'sche Theorie und das Migrationsgesetz
der Organismen' 1868 page 19.) remarks, one kind alone exists there. The ass
in England varies much in colour and size; but as it is an animal of little
value and bred by poor people, there has been no selection, and distinct races
have not been formed. We must not attribute the inferiority of our asses to
climate, for in India they are of even smaller size than in Europe. But when
selection is brought to bear on the ass, all is changed. Near Cordova, as I am
informed (February 1860) by Mr. W.E. Webb, C.E., they are carefully bred, as
much as 200 pounds having been paid for a stallion ass, and they have been
immensely improved. In Kentucky, asses have been imported (for breeding mules)
from Spain, Malta, and France; these "seldom averaged more than fourteen hands
high: but the Kentuckians, by great care, have raised them up to fifteen
hands, and sometimes even to sixteen. The prices paid for these splendid
animals, for such they really are, will prove how much they are in request.
One male, of great celebrity, was sold for upwards of one thousand pounds
sterling." These choice asses are sent to cattle-shows, a day being given for
their exhibition. (21/50. Capt. Marryat quoted by Blyth in 'Journ. Asiatic
Soc. of Bengal' volume 28 page 229.)
Analogous facts have been observed with plants: the nutmeg-tree in the Malay
archipelago is highly variable, but there has been no selection, and there are
no distinct races. (21/51. Mr. Oxley 'Journal of the Indian Archipelago'
volume 2 1848 page 645.) The common mignonette (Reseda odorata), from bearing
inconspicuous flowers, valued solely for their fragrance, "remains in the same
unimproved condition as when first introduced." (21/52. Mr. Abbey 'Journal of
Horticulture' December 1, 1863 page 430.) Our common forest-trees are very
variable, as may be seen in every extensive nursery-ground; but as they are
not valued like fruit-trees, and as they seed late in life, no selection has
been applied to them; consequently, as Mr. Patrick Matthews remarks (21/53.
'On Naval Timber' 1831 page 107.), they have not yielded distinct races,
leafing at different periods, growing to different sizes, and producing timber
fit for different purposes. We have gained only some fanciful and semi-
monstrous varieties, which no doubt appeared suddenly as we now see them.
Some botanists have argued that plants cannot have so strong a tendency to
vary as is generally supposed, because many species long grown in botanic
gardens, or unintentionally cultivated year after year mingled with our corn
crops, have not produced distinct races; but this is accounted for by slight
variations not having been selected and propagated. Let a plant which is now
grown in a botanic garden, or any common weed, be cultivated on a large scale,
and let a sharp-sighted gardener look out for each slight variety and sow the
seed, and then, if distinct races are not produced, the argument will be
valid.
The importance of selection is likewise shown by considering special
characters. For instance, with most breeds of fowls the form of the comb and
the colour of the plumage have been attended to, and are eminently
characteristic of each race; but in Dorkings fashion has never demanded
uniformity of comb or colour; and the utmost diversity in these respects
prevails. Rose-combs, double-combs, cup-combs, etc., and colours of all kinds,
may be seen in purely bred and closely related Dorking fowls, whilst other
points, such as the general form of body, and the presence of an additional
toe, have been attended to, and are invariably present. It has also been
ascertained that colour can be fixed in this breed, as well as in any other.
(21/54. Mr. Baily in 'The Poultry Chronicle' volume 2 1854 page 150. Also
volume 1 page 342; volume 3 page 245.)
During the formation or improvement of a breed, its members will always be
found to vary much in those characters to which especial attention is
directed, and of which each slight improvement is eagerly sought and selected.
Thus, with short-faced tumbler-pigeons, the shortness of the beak, shape of
head and plumage,--with carriers, the length of the beak and wattle,--with
fantails, the tail and carriage,--with Spanish fowls, the white face and
comb,--with long-eared rabbits, the length of ear, are all points which are
eminently variable. So it is in every case; and the large price paid for
first-rate animals proves the difficulty of breeding them up to the highest
standard of excellence. This subject has been discussed by fanciers (21/55.
'Cottage Gardener' 1855 December page 171; 1856 January pages 248, 323.), and
the greater prizes given for highly improved breeds, in comparison with those
given for old breeds which are not now undergoing rapid improvement, have been
fully justified. Nathusius makes (21/56. 'Ueber Shorthorn Rindvieh' 1857 s.
51.) a similar remark when discussing the less uniform character of improved
Shorthorn cattle and of the English horse, in comparison, for example, with
the unennobled cattle of Hungary, or with the horses of the Asiatic steppes.
This want of uniformity in the parts which at the time are undergoing
selection chiefly depends on the strength of the principle of reversion; but
it likewise depends to a certain extent on the continued variability of the
parts which have recently varied. That the same parts do continue varying in
the same manner we must admit, for if it were not so, there could be no
improvement beyond an early standard of excellence, and we know that such
improvement is not only possible, but is of general occurrence.
As a consequence of continued variability, and more especially of reversion,
all highly improved races, if neglected or not subjected to incessant
selection, soon degenerate. Youatt gives a curious instance of this in some
cattle formerly kept in Glamorganshire; but in this case the cattle were not
fed with sufficient care. Mr. Baker, in his memoir on the Horse, sums up: "It
must have been observed in the preceding pages that, whenever there has been
neglect, the breed has proportionally deteriorated." (21/57. 'The Veterinary'
volume 13 page 720. For the Glamorganshire cattle see Youatt on 'Cattle' page
51.) If a considerable number of improved cattle, sheep, or other animals of
the same race, were allowed to breed freely together, with no selection, but
with no change in their condition of life, there can be no doubt that after a
score or hundred generations they would be very far from excellent of their
kind; but, from what we see of the many common races of dogs, cattle, fowls,
pigeons, etc., which without any particular care have long retained nearly the
same character, we have no grounds for believing that they would altogether
depart from their type.
It is a general belief amongst breeders that characters of all kinds become
fixed by long-continued inheritance. But I have attempted to show in the
fourteenth chapter that this belief apparently resolves itself into the
following proposition, namely, that all characters whatever, whether recently
acquired or ancient, tend to be transmitted, but that those which have already
long withstood all counteracting influences, will, as a general rule, continue
to withstand them, and consequently be faithfully transmitted.
TENDENCY IN MAN TO CARRY THE PRACTICE OF SELECTION TO AN EXTREME POINT.
It is an important principle that in the process of selection man almost
invariably wishes to go to an extreme point. Thus, there is no limit to his
desire to breed certain kinds of horses and dogs as fleet as possible, and
others as strong as possible; certain kinds of sheep for extreme fineness, and
others for extreme length of wool; and he wishes to produce fruit, grain,
tubers, and other useful parts of plants, as large and excellent as possible.
With animals bred for amusement, the same principle is even more powerful; for
fashion, as we see in our dress, always runs to extremes. This view has been
expressly admitted by fanciers. Instances were given in the chapters on the
pigeon, but here is another: Mr. Eaton, after describing a comparatively new
variety, namely, the Archangel, remarks, "What fanciers intend doing with this
bird I am at a loss to know, whether they intend to breed it down to the
tumbler's head and beak, or carry it out to the carrier's head and beak;
leaving it as they found it, is not progressing." Ferguson, speaking of fowls,
says, "their peculiarities, whatever they may be, must necessarily be fully
developed: a little peculiarity forms nought but ugliness, seeing it violates
the existing laws of symmetry." So Mr. Brent, in discussing the merits of the
sub-varieties of the Belgian canary-bird, remarks, "Fanciers always go to
extremes; they do not admire indefinite properties." (21/58. J.M. Eaton 'A
Treatise on Fancy Pigeons' page 82; Ferguson on 'Rare and Prize Poultry' page
162; Mr. Brent in 'Cottage Gardener' October 1860 page 13.)
This principle, which necessarily leads to divergence of character, explains
the present state of various domestic races. We can thus see how it is that
racehorses and dray-horses, greyhounds and mastiffs, which are opposed to each
other in every character,--how varieties so distinct as Cochin-china fowls and
bantams, or carrier-pigeons with very long beaks, and tumblers with
excessively short beaks, have been derived from the same stock. As each breed
is slowly improved, the inferior varieties are first neglected and finally
lost. In a few cases, by the aid of old records, or from intermediate
varieties still existing in countries where other fashions have prevailed, we
are enabled partially to trace the graduated changes through which certain
breeds have passed. Selection, whether methodical or unconscious, always
tending towards an extreme point, together with the neglect and slow
extinction of the intermediate and less-valued forms, is the key which unlocks
the mystery of how man has produced such wonderful results.
In a few instances selection, guided by utility for a single purpose, has led
to convergence of character. All the improved and different races of the pig,
as Nathusius has well shown (21/59. 'Die Racen des Schweines' 1860 s. 48.),
closely approach each other in character, in their shortened legs and muzzles,
their almost hairless, large, rounded bodies, and small tusks. We see some
degree of convergence in the similar outline of the body in well-bred cattle
belonging to distinct races. (21/60. See some good remarks on this head by M.
de Quatrefages 'Unite de l'Espece Humaine' 1861 page 119.) I know of no other
such cases.
Continued divergence of character depends on, and is indeed a clear proof, as
previously remarked, of the same parts continuing to vary in the same
direction. The tendency to mere general variability or plasticity of
organisation can certainly be inherited, even from one parent, as has been
shown by Gartner and Kolreuter, in the production of varying hybrids from two
species, of which one alone was variable. It is in itself probable that, when
an organ has varied in any manner, it will again vary in the same manner, if
the conditions which first caused the being to vary remain, as far as can be
judged, the same. This is either tacitly or expressly admitted by all
horticulturists: if a gardener observes one or two additional petals in a
flower, he feels confident that in a few generations he will be able to raise
a double flower, crowded with petals. Some of the seedlings from the weeping
Moccas oak were so prostrate that they only crawled along the ground. A
seedling from the fastigiate or upright Irish yew is described as differing
greatly from the parent-form "by the exaggeration of the fastigiate habit of
its branches." (21/61. Verlot 'Des Varietes' 1865 page 94.) Mr. Shirreff, who
has been highly successful in raising new kinds of wheat, remarks, "A good
variety may safely be regarded as the forerunner of a better one." (21/62. Mr.
Patrick Shirreff 'Gardener's Chronicle' 1858 page 771.) A great rose-grower,
Mr. Rivers, has made the same remark with respect to roses. Sageret (21/63.
'Pomologie Physiolog.' 1830 page 106.), who had large experience, in speaking
of the future progress of fruit-trees, observes that the most important
principle is "that the more plants have departed from their original type, the
more they tend to depart from it." There is apparently much truth in this
remark; for we can in no other way understand the surprising amount of
difference between varieties in the parts or qualities which are valued,
whilst other parts retain nearly their original character.
The foregoing discussion naturally leads to the question, what is the limit to
the possible amount of variation in any part or quality, and, consequently, is
there any limit to what selection can effect? Will a racehorse ever be reared
fleeter than Eclipse? Can our prize-cattle and sheep be still further
improved? Will a gooseberry ever weigh more than that produced by "London" in
1852? Will the beet-root in France yield a greater percentage of sugar? Will
future varieties of wheat and other grain produce heavier crops than our
present varieties? These questions cannot be positively answered; but it is
certain that we ought to be cautious in answering them by a negative. In some
lines of variation the limit has probably been reached. Youatt believes that
the reduction of bone in some of our sheep has already been carried so far
that it entails great delicacy of constitution. (21/64. Youatt on 'Sheep' page
521.) But seeing the great improvement within recent times in our cattle and
sheep, and especially in our pigs; seeing the wonderful increase in weight in
our poultry of all kinds during the last few years; he would be a bold man who
would assert that perfection has been reached. It has often been said that
Eclipse never was, and never will be, beaten in speed by any other horse; but
on making inquiries I find that the best judges believe that our present
racehorses are fleeter. (21/65. See also Stonehenge 'British Rural Sports'
edition of 1871 page 384.) The attempt to raise a new variety of wheat more
productive than the many old kinds, might have been thought until lately quite
hopeless; but this has been effected by Major Hallett, by careful selection.
With respect to almost all our animals and plants, those who are best
qualified to judge do not believe that the extreme point of perfection has yet
been reached even in the characters which have already been carried to a high
standard. For instance, the short-faced tumbler-pigeon has been greatly
modified; nevertheless, according to Mr. Eaton (21/66. 'A Treatise on the
Almond Tumbler' page 1.) "the field is still as open for fresh competitors as
it was one hundred years ago." Over and over again it has been said that
perfection had been attained with our flowers, but a higher standard has soon
been reached. Hardly any fruit has been more improved than the strawberry, yet
a great authority remarks (21/67. M. J. de Jonghe in 'Gardener's Chronicle'
1858 page 173.), "it must not be concealed that we are far from the extreme
limits at which we may arrive."
No doubt there is a limit beyond which the organisation cannot be modified
compatibly with health or life. The extreme degree of fleetness, for instance,
of which a terrestrial animal is capable, may have been acquired by our
present racehorses; but as Mr. Wallace has well remarked (21/68.
'Contributions to the Theory of Natural Selection' 2nd edition 1871 page
292.), the question that interests us, "is not whether indefinite and
unlimited change in any or all directions is possible, but whether such
differences as do occur in nature could have been produced by the accumulation
of varieties by selection." And in the case of our domestic productions, there
can be no doubt that many parts of the organisation, to which man has
attended, have been thus modified to a greater degree than the corresponding
parts in the natural species of the same genera or even families. We see this
in the form and size of our light and heavy dogs or horses,--in the beak and
many other characters of our pigeons,--in the size and quality of many
fruits,--in comparison with the species belonging to the same natural groups.
Time is an important element in the formation of our domestic races, as it
permits innumerable individuals to be born, and these when exposed to
diversified conditions are rendered variable. Methodical selection has been
occasionally practised from an ancient period to the present day, even by
semi-civilised people, and during former times will have produced some effect.
Unconscious selection will have been still more effective; for during a
lengthened period the more valuable individual animals will occasionally have
been saved, and the less valuable neglected. In the course of time, different
varieties, especially in the less civilised countries, will also have been
more or less modified through natural selection. It is generally believed,
though on this head we have little or no evidence, that new characters in time
become fixed; and after having long remained fixed it seems possible that
under new conditions they might again be rendered variable.
How great the lapse of time has been since man first domesticated animals and
cultivated plants, we begin dimly to see. When the lake-dwellings of
Switzerland were inhabited during the Neolithic period, several animals were
already domesticated and various plants cultivated. The science of language
tells us that the art of ploughing and sowing the land was followed, and the
chief animals had been already domesticated, at an epoch so immensely remote,
that the Sanskrit, Greek, Latin, Gothic, Celtic, and Sclavonic languages had
not as yet diverged from their common parent-tongue. (21/69. Max Muller
'Science of Language' 1861 page 223.)
It is scarcely possible to overrate the effects of selection occasionally
carried on in various ways and places during thousands of generations. All
that we know, and, in a still stronger degree, all that we do not know (21/70.
'Youatt on Cattle' pages 116, 128.), of the history of the great majority of
our breeds, even of our more modern breeds, agrees with the view that their
production, through the action of unconscious and methodical selection, has
been almost insensibly slow. When a man attends rather more closely than is
usual to the breeding of his animals, he is almost sure to improve them to a
slight extent. They are in consequence valued in his immediate neighbourhood,
and are bred by others; and their characteristic features, whatever these may
be, will then slowly but steadily be increased, sometimes by methodical and
almost always by unconscious selection. At last a strain, deserving to be
called a sub-variety, becomes a little more widely known, receives a local
name, and spreads. The spreading will have been extremely slow during ancient
and less civilised times, but now is rapid. By the time that the new breed had
assumed a somewhat distinct character, its history, hardly noticed at the
time, will have been completely forgotten; for, as Low remarks (21/71.
'Domesticated Animals' page 188.), "we know how quickly the memory of such
events is effaced."
As soon as a new breed is thus formed, it is liable through the same process
to break up into new strains and sub-varieties. For different varieties are
suited for, and are valued under, different circumstances. Fashion changes,
but, should a fashion last for even a moderate length of time, so strong is
the principle of inheritance, that some effect will probably be impressed on
the breed. Thus varieties go on increasing in number, and history shows us how
wonderfully they have increased since the earliest records. (21/72. Volz
'Beitrage zur Kulturgeschichte' 1852 s. 99 et passim.) As each new variety is
produced, the earlier, intermediate, and less valuable forms will be
neglected, and perish. When a breed, from not being valued, is kept in small
numbers, its extinction almost inevitably follows sooner or later, either from
accidental causes of destruction or from close interbreeding; and this is an
event which, in the case of well-marked breeds, excites attention. The birth
or production of a new domestic race is so slow a process that it escapes
notice; its death or destruction is comparatively sudden, is often recorded,
and when too late sometimes regretted.
Several authors have drawn a wide distinction between artificial and natural
races. The latter are more uniform in character, possessing in a high degree
the appearance of natural species, and are of ancient origin. They are
generally found in less civilised countries, and have probably been largely
modified by natural selection, and only to a small extent by man's unconscious
and methodical selection. They have, also, during a long period, been directly
acted on by the physical conditions of the countries which they inhabit. The
so-called artificial races, on the other hand, are not so uniform in
character; some have a semi-monstrous character, such as "the wry-legged
terriers so useful in rabbit-shooting" (21/73. Blaine 'Encyclop. of Rural
Sports' page 213.), turnspit dogs, ancon sheep, niata oxen, Polish fowls,
fantail-pigeons, etc.; their characteristic features have generally been
acquired suddenly, though subsequently increased by careful selections in many
cases. Other races, which certainly must be called artificial, for they have
been largely modified by methodical selection and by crossing, as the English
racehorse, terrier-dogs, the English game-cock, Antwerp carrier-pigeons, etc.,
nevertheless cannot be said to have an unnatural appearance; and no distinct
line, as it seems to me, can be drawn between natural and artificial races.
It is not surprising that domestic races should generally present a different
aspect from natural species. Man selects and propagates modifications solely
for his own use or fancy, and not for the creature's own good. His attention
is struck by strongly marked modifications, which have appeared suddenly, due
to some great disturbing cause in the organisation. He attends almost
exclusively to external characters; and when he succeeds in modifying internal
organs,--when for instance he reduces the bones and offal, or loads the
viscera with fat, or gives early maturity, etc.-the chances are strong that he
will at the same time weaken the constitution. On the other hand, when an
animal has to struggle throughout its life with many competitors and enemies,
under circumstances inconceivably complex and liable to change, modifications
of the most varied nature in the internal organs as well as in external
characters, in the functions and mutual relations of parts, will be rigorously
tested, preserved, or rejected. Natural selection often checks man's
comparatively feeble and capricious attempts at improvement; and if it were
not so, the result of his work, and of nature's work, would be even still more
different. Nevertheless, we must not overrate the amount of difference between
natural species and domestic races; the most experienced naturalists have
often disputed whether the latter are descended from one or from several
aboriginal stocks, and this clearly shows that there is no palpable difference
between species and races.
Domestic races propagate their kind far more truly, and endure for munch
longer periods, than most naturalists are willing to admit. Breeders feel no
doubt on this head: ask a man who has long reared Shorthorn or Hereford
cattle, Leicester or Southdown sheep, Spanish or Game poultry, tumbler or
carrier-pigeons, whether these races may not have been derived from common
progenitors, and he will probably laugh you to scorn. The breeder admits that
he may hope to produce sheep with finer or longer wool and with better
carcases, or handsomer fowls, or carrier-pigeons with beaks just perceptibly
longer to the practised eye, and thus be successful at an exhibition. Thus far
he will go, but no farther. He does not reflect on what follows from adding up
during a long course of time many slight, successive modifications; nor does
he reflect on the former existence of numerous varieties, connecting the links
in each divergent line of descent. He concludes, as was shown in the earlier
chapters, that all the chief breeds to which he has long attended are
aboriginal productions. The systematic naturalist, on the other hand, who
generally knows nothing of the art of breeding, who does not pretend to know
how and when the several domestic races were formed, who cannot have seen the
intermediate gradations, for they do not now exist, nevertheless feels no
doubt that these races are sprung from a single source. But ask him whether
the closely allied natural species which he has studied may not have descended
from a common progenitor, and he in his turn will perhaps reject the notion
with scorn. Thus the naturalist and breeder may mutually learn a useful lesson
from each other.
SUMMARY ON SELECTION BY MAN.
There can be no doubt that methodical selection has effected and will effect
wonderful results. It was occasionally practised in ancient times, and is
still practised by semi-civilised people. Characters of the highest
importance, and others of trifling value, have been attended to, and modified.
I need not here repeat what has been so often said on the part which
unconscious selection has played: we see its power in the difference between
flocks which have been separately bred, and in the slow changes, as
circumstances have slowly changed, which many animals have undergone in the
same country, or when transported into a foreign land. We see the combined
effects of methodical and unconscious selection, in the great amount of
difference in those parts or qualities which are valued by man in comparison
with the parts which are not valued, and consequently have not been attended
to. Natural selection often determines man's power of selection. We sometimes
err in imagining that characters, which are considered as unimportant by the
systematic naturalist, could not be affected by the struggle for existence,
and could not be acted on by natural selection; but striking cases have been
given, showing how great an error this is.
The possibility of selection coming into action rests on variability; and this
is mainly caused, as we shall hereafter see, by changes in the conditions of
life. Selection is sometimes rendered difficult, or even impossible, by the
conditions being opposed to the desired character or quality. It is sometimes
checked by the lessened fertility and weakened constitution which follow from
long-continued close interbreeding. That methodical selection may be
successful, the closest attention and discernment, combined with unwearied
patience, are absolutely necessary; and these same qualities, though not
indispensable, are highly serviceable in the case of unconscious selection. It
is almost necessary that a large number of individuals should be reared; for
thus there will be a fair chance of variations of the desired nature arising,
and of every individual with the slightest blemish or in any degree inferior
being freely rejected. Hence length of time is an important element of
success. Thus, also, reproduction at an early age and at short intervals
favours the work. Facility in pairing animals, or their inhabiting a confined
area, is advantageous as a check to free crossing. Whenever and wherever
selection is not practised, distinct races are not formed within the same
country. When any one part of the body or one quality is not attended to, it
remains either unchanged or varies in a fluctuating manner, whilst at the same
time other parts and other qualities may become permanently and greatly
modified. But from the tendency to reversion and to continued variability,
those parts or organs which are now undergoing rapid improvement through
selection, are likewise found to vary much. Consequently highly-bred animals
when neglected soon degenerate; but we have no reason to believe that the
effects of long-continued selection would, if the conditions of life remained
the same, be soon and completely lost.
Man always tends to go to an extreme point in the selection, whether
methodical or unconscious, of all useful and pleasing qualities. This is an
important principle, as it leads to continued divergence, and in some rare
cases to convergence of character. The possibility of continued divergence
rests on the tendency in each part or organ to go on varying in the same
manner in which it has already varied; and that this occurs, is proved by the
steady and gradual improvement of many animals and plants during lengthened
periods. The principle of divergence of character, combined with the neglect
and final extinction of all previous, less-valued, and intermediate varieties,
explains the amount of difference and the distinctness of our several races.
Although we may have reached the utmost limit to which certain characters can
be modified, yet we are far from having reached, as we have good reason to
believe, the limit in the majority of cases. Finally, from the difference
between selection as carried on by man and by nature, we can understand how it
is that domestic races often, though by no means always, differ in general
aspect from closely allied natural species.
Throughout this chapter and elsewhere I have spoken of selection as the
paramount power, yet its action absolutely depends on what we in our ignorance
call spontaneous or accidental variability. Let an architect be compelled to
build an edifice with uncut stones, fallen from a precipice. The shape of each
fragment may be called accidental; yet the shape of each has been determined
by the force of gravity, the nature of the rock, and the slope of the
precipice,--events and circumstances, all of which depend on natural laws; but
there is no relation between these laws and the purpose for which each
fragment is used by the builder. In the same manner the variations of each
creature are determined by fixed and immutable laws; but these bear no
relation to the living structure which is slowly built up through the power of
selection, whether this be natural or artificial selection.
If our architect succeeded in rearing a noble edifice, using the rough wedge-
shaped fragments for the arches, the longer stones for the lintels, and so
forth, we should admire his skill even in a higher degree than if he had used
stones shaped for the purpose. So it is with selection, whether applied by man
or by nature; for although variability is indispensably necessary, yet, when
we look at some highly complex and excellently adapted organism, variability
sinks to a quite subordinate position in importance in comparison with
selection, in the same manner as the shape of each fragment used by our
supposed architect is unimportant in comparison with his skill.