222 



KNOVSTLEDGE ♦ 



[August 1, 1888. 



ill an animal whose life depsnds on its not becoming the 

 prey of carnivoi'ous animals. We can understand how, in 

 certain regions, those members of feline races who chanced 

 to have markings on their bodies which corresponded in 

 appearance with the stems of trees, or with jungle reeds, and 

 the like, would be better able to remain concealed till the 

 animals which formed their prey came within range of their 

 spring, and so would have the best chances of living — for 

 carnivorous propensities have their life-supporting as well as 

 their life-destroying aspect. And in like manner, although 

 the zebra is chiefly protected from carnivorous enemies by 

 his almost unrivalled speed, yet the zebra has his occasions 

 for rest and sleep, and it is manifestly to his advantage, 

 when sleeping in the shade of trees, to have markings on his 

 body which from a distance would be confounded with the 

 stems of trees and shrubs beneath which for awhile his 

 active limbs were at rest. For so would he best escape 

 the attacks of animals of prey. 



It is noteworthy that when the zebra is stretched on the 

 ground the stripes on his legs as well as those on his body 

 are vertical as seen from a distance. The same is the case 

 with the tiger's stripes when the animal is couched for a 

 spring. 



We can understand then how in the course of many 

 generations the tiger would develop his stripes to aid 

 him in attack, and the zebra develop his to give him safety 

 — for the less striped of either race would have the worst 

 chances in life's struggle, and so be steadily eliminated from 

 the stock — as surely (in the long run) though not as uni- 

 formly as the inferior members of flocks and herds are re- 

 moved by the breeder. In like manner and to like advan- 

 tage, the leopard and the jaguar have their spots, simula- 

 ting the spotted shade of leaf-bearing trees, the lion has his 

 sand-hued body, the antelope (besides his speed) his colour 

 akin to the surface over which he urges his course, and so 

 forth. Some animals even change in colour with the 

 season, or aro modified according to liabits ; for instance, 

 the alpine ptarmigan is white in winter, and the red grouse 

 resembles in colour tlie heather ; leaf-eating insscts are 

 green ; those which feed on the bark are grey, or brown, or 

 mottled. 



Apart from the interest which such cases have in them- 

 selves (to mention only thsse few, and not the thousands 

 whose mere names would fill all the space available to me), 

 there is singular, to me imj^ressive, interest in the evidence 

 which these characteristic colours and markings carry with 

 them, even through untold ages, of their origin and persist- 

 ence. <-)nly a few minutes ago there passed across the porch 

 outside my study window a sandy-coloured cat marked with 

 stripes such as hundreds of thousands of years ago were of 

 value to its remote ancestors in the struggle for life. Bat 

 though it is wonderful to see such a feature as this handed 

 down through generation after generation after the time 

 when tliey were of essential use in the struggle for life, 

 there is something to me even more impressive in the latent 

 continuance of such characteristics. A few minutes ago I 

 saw ploughing a field of mine a mule, round whose legs, near 

 the joints which we call the knees in the forelegs and the 

 hocks in tlie hind legs (really corresponding to the wrists 

 and heels of man), are seven or eight rings precisely corre- 

 sponding to the rings round the corresponding parts of his 

 remote ancestor, the zebra. Through thousands of genera- 

 tions, in the horse and the ass, these stripes have as it were 

 remained dormant — though for aught I know they may 

 have occasionally shown themselves in particular individuals, 

 even as in particular men special monkey or ape-like traits 

 may show themselves. But, as we know, such markings 

 are so exceptional among horses and among asses that the 

 animals showing them are regarded almost as monstrosities. 



Yet there has been lying in wait in the blood of both races, 

 during hundreds of thousands of years, this particular trait 

 of the wild ancestral race, ready to show itself when the two 

 descended races should be crossed. The case is akin to the 

 appearance, when breeds of fancy pigeons are crossed, of 

 young which are scarcely to be distinguished from the wild 

 ancestral rock-pigeon ; but iu one case we can trace back 

 the line on either side to the blue rock-pigeons through a 

 limited range of removals. In the other we have the 

 immense range of time to deal with which separates the 

 branching off of the equine and asinine stocks out of that 

 particular family of hippie animals from which the descent 

 of both began. 



The colouring of animals i-i not always of this simply 

 protective character, however, though always (so far as cm 

 be judged) playing an important part in developments. 

 There are some cases in which it has been found diffisult, 

 even impossible, to account for the ditt'erence which 

 undoubtedly exists in regard to the struggle for life 

 between animals of the same class difl'erently coloured. In 

 the human race itself we find races of different colour 

 affected in different degrees by specific diseases. " The 

 colour of the skin," says Darwiu, " is sometimes correlated 

 in a surprising manner with a complete immunity from 

 the action of certain vegetable poisons, and from the 

 attacks of certain parasites. Negroes and mulattoes 

 are almost entirely exempt from yellow fever and 

 from the intermittent fevers which prevail along the 

 shores of Africa. The susceptibility of animals to the 

 attacks of insects is found to be correlated with colour. So 

 also is the liability to be poisoned by particular plants." 

 Professor Wyman informed Darwin that the farmers in 

 Virginia found only black pigs cajjable of resisting the 

 effects of paint root. White sheep and pigs are injured by 

 plants on which the darker-coloured animals can feed with 

 impunity. Hundreds of such cases could be cited. 



In another respect colour plays an important part, viz., 

 in influencing sexual selection. It is not as yet easy to 

 say in some cases whether this or some protective or con- 

 cealing influence is really in question. Thus, as Darwin 

 remarks, the colour of the green woodpecker seems " a 

 beautiful adaptation to conceal this tree-frequenting animal 

 from its enemies ; " but we know that there are many black 

 .and pied varieties, so that he concludes that " the colour is 

 probably due in chief part to sexual selection." It does not 

 seem clear that in this particular case the latter interpreta- 

 tion is forced upon us — since most of the pied varieties 

 seem as well protected by their colour as the green ; and, 

 in fact, we find them for the most part frequenting trees 

 whose bark or foliage harmonises with their own prevailing 

 tints. Moreover, we have already seen that the insects on 

 which woodpecker's live, including leaf-eaters and bark- 

 feeders, are diversely coloured to correspond with these 

 special habits. Why should not tlie same variety be found 

 among the birds which seek them 1 Even the red-headed 

 woodpecker is not quite certainly to be regarded as an 

 exception ; still in his case sexu.al selection seems to be the 

 explanation naturally suggested. In many cases there can 

 be no doubt that peculiarities of colour in animals of various 

 kinds have been developed mainly in virtue of natural 

 selection, or have at least been carried f;u- beyond the 

 requirements of mere protection. 



In the vegetable world colour seems to be in all cases 

 dependent on the requirements of propagation. Thus where 

 seeds are diffused by animals, as with the berries, we find 

 the fruits brightly coloured to attract the attention of the 

 animal distributors. It may be noticed that where seeds 

 are distributed by the winds bright colours are not found in 

 the fruit, even though the plant be closely allied to species 



