CHAPTER XXI.

SELECTION, continued.

REAL

NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS CHARACTERS WHICH APPEAR OF TRIFLING VALUE OFTEN OF IMPORTANCECIRCUMSTANCES 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 ΤΟ 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

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preceding one; and when the spring was severe, seldom 66 more than two-thirds of the lambs survived the ravages of "the storms." 99 1 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.2

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,3 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.

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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." 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 viii., 1861, p. 311.

1 Quoted by Youatt on Sheep, p. 325. See also Youatt on Cattle, pp. 62, 69.

2 MM. Lherbette and De Quatrefages, in Bull. Soc. d'Acclimat.,' tom.

3 The Poultry Book,' 1866, p. 123. Mr. Tegetmeier, The Homing or Carrier Pigeon,' 1871, pp. 45-58.

Youatt on Sheep, p. 312.

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, "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 longcontinued 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, &c.; this the 5 Treatise on the Almond Tumbler,' 1851, p. 33.

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. Complexion, and liability to certain diseases, are believed Dr. Heusinger, Wochenschrift für die Heilkunde,' Berlin, 1846, s. 279.

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7

to run together in man and the lower animals. Thus white terriers suffer more than those of any other colour from the fatal distemper. In North America plum-trees are liable to a disease which Downings 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." 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 darkcoloured chickens to the gapes, which is caused by a parasitic worm in the trachea.10 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.11 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.12 White verbenas are especially liable to mildew.13 Near Malaga, during an early period of the vine