September 24, 1908] 



NA rURE 



527 



we can find a family of lower animals who cannot be 

 said to have thus migrated, and who show the effects of 

 environment, we shall be able to argue powerfully from 

 analogy. 



The horse family supplies the example required. If we 

 follow it from Northern Asia to the Cape of Good Hope, 

 we shall find that every belt has its own particular type, 

 changes in osteology as well as in coloration taking place 

 from region to region. First we meet the old dun horse, 

 with its tendency to become white, the best European 

 examples of which were probably the now extinct ponies 

 of the Lofoden Isles. In .Asia, PrejvalsUy's horse is the 

 best living instance — a dun-coloured animal with little 

 trace of stripes. Bordering on the Prejvalsky horse or 

 true tarpan come the Asiatic asses : first the dzeggetai of 

 Mongolia, a faw'n-coloured animal, the under-parts being 

 Isabella-coloured; then comes the kiang of the Upper Indus 

 valley, seldom found at a lower altitude than 10,000 feet, 

 rufous-brown with white under-parts, whilst, as might 

 be expected from its mountain habitat, its hind-quarters 

 are much more developed in length and strength than in 

 the asses of the plains. The Onagi:f indicus, onager and 

 hcmippus are found in all the great plains of the Punjab, 

 Afghanistan, Western India, Baluchistan, Persia, and 

 Syria, whilst a few are said to survive in South .Arabia. 

 All these are lighter in colour than the kiang, the typical 

 onager being a white animal with yellow blotches on the 

 side, neck, and head. .AH the Asiatic asses are dis- 

 tinguished by the absence of any shoulder stripe, though 

 they occasionally show traces of stripes on the lower parts 

 of the legs. The southern Asiatic asses just described, in 

 their greyer colour and smaller hoofs approximate to the 

 wild asses of Africa, especially to those of Somaliland, 

 whilst it is maintained that in their cry, as well as in 

 their colour, the kiang and dzeggetai come closer to the 

 horse, the next neighbours of which they are. 



Passing to .Africa, we find the ass of Nubia and 

 Abyssinia showing a shoulder stripe, and frequently with 

 very strongly defined narrow stripes on the legs, the ears 

 being longer than those of the onager. But in closer 

 proximity to South-Western .Asia comes the Somali ass, 

 which differs from those of Nubia and Abyssinia by being 

 greyer in colour, by the entire absence of shoulder stripes, 

 and by smaller ears, in all which characteristics it comes 

 closer to its neighbours on the .Asiatic side than it does 

 to its relations in Abyssinia and Nubia. 



Next we meet the zebras. First comes the magnificent 

 Gr^vy zebra of Somaliland, Shoa, and British East .Africa. 

 It is completely striped down to its hoofs, but the colora- 

 tion of the specimens from Shoa differs from that of those 

 from Somaliland and from those of British East .Africa. 

 The Gr^vy zebra has its hoofs rounded in front like those 

 of a horse, but its ears are more like its neighbours the 

 asses than those of anv other zebra. 



In the region north of the river Tana the Burchelline 

 group of zebras overlaps the Gr^vy, and though it differs 

 essentially in form, habits, and shape of its hoofs from 

 the Gr^vy, some of those in the neighbourhood of Lake 

 Barringo show grid-iron markincs on the croup like those 

 on the Gr^vy zebra, whilst, like the latter, they also 

 possess functional premolars. 



.All the zebras of the equatorial regions are striped to the 

 hoofs, but when we roach the Transvaal, the Burchelline 

 zebra, known as Chapman's, is divesting itself of stripes 

 on its legs, whilst the ground colour is getting less white 

 and the stripes less black. Further south the true Burchell 

 zebra of the Orange River has completely lost the stripes 

 on its legs and under-surface, its general colouring being 

 a pale yellowish-brown, the stripes being dark brown or 

 nearly black. South of the Orange River the now extinct 

 quagga of Cape Colony had not only begun to lose the 

 stripes of its under-part and on the hind-quarters, but in 

 Daniell's specimen they only survived on the neck as far 

 as the withers, the animal having its upper surface bay 

 and a tail like that of a horse, whilst all specimens of 

 quagga show a rounded hoof like that of a horse. 



In the quagga of 30° to 32° S. we have practically a bay 

 horse corresponding to the bav Libvan horse of lat. 

 30°-32° N. 



But the production of such variations in colour does not 

 require great differences in latitude. On the contrary, | 



NO. 2030, VOL. 78] 



from a study of a series of skins of zebras shot for me in- 

 British East Africa, each of which is from a known locality 

 and from a known altitude, there can be no doubt that 

 such variations in colour are found from district to district 

 within a comparatively small area. 



In addition to the two species of zebra already mentioned, 

 there is the mountain zebra, formerly extremely common 

 in the mountainous parts of Cape Colony and Natal, though, 

 now nearly extinct in that area. Its hind legs, as might 

 naturally have been expected from its habitat, are more 

 developed than those of the other zebras, just as these 

 same limbs are also more developed in the kiang of the 

 Himalayas than in any other ass. 



With these facts before us, there can be no doubt that 

 environment is a most potent factor, not only in coloration, 

 but also in osteology. No less certain is it that environ- 

 ment is capable of producing changes in animal types with 

 great rapidity. Thus, although it is an historical fact 

 that there were no horses in Java in 1346, and it is known, 

 that the ponies now there are descended from those broiight 

 in by the .Arabs, yet within five centuries there has arisen 

 a race of ponies (.often striped) some of which are not 

 more than two feet high. Darwin himself has given 

 other examples of the rapid change in structure of horses 

 when transferred from one environment to another, as, for 

 instance, when Pampas horses are brought up into the 

 .Andes. 



-Another good example is that of the now familiar Basuto 

 ponies. Up to 1846 the Basutos did not possess a single 

 horse, those of them who went down and worked for the 

 Boers of the Orange River usually taking their pay ia' 

 cattle. At the date mentioned some of them began to 

 take horses instead. These horses were of the ordinary 

 mixed colonial kinds, and we may be sure that the Boers 

 did not let the Basutos have picked specimens. The- 

 Basutos turned these horses out on their mountains, where, 

 living under perfectly natural conditions, their posterity 

 within less than forty years had settled down into a well- 

 defined tvpe of mountain pony. 



Nor is' it only in the horse family that we meet with 

 examples of the force of environment. The tiger extends 

 from the Indian Ocean, through China up to Corea, but 

 the tiger of Corea is a very different animal from that of 

 Bengal. Instead of the sho'rt hair of the Indian tiger, the 

 Corean has clothed himself with a robe of dense long fur 

 to withstand the rigours of the north. It is not unlikely 

 that if we had a sufficient number of skins from known 

 localities we could trace the change in the tiger from 

 latitude to latitude, just as I have shown in the case of 

 the Equidse. 



Now whilst there is certainly a general physical type 

 common to all the peoples round the Mediterranean, it 

 bv no means follows that all those peoples are from the 

 same original stock. On the contrary, the analogy from 

 man in other parts of the Avorld, as w-ell as that of the 

 Equid.-e, suggest that the resemblance between the Berbers, 

 who speak Hamitic, the Greeks who speak Aryan, and 

 the Jews and .Arabs who spoke Semitic, is simply due 

 to the fact that those peoples, from having long dwelt 

 under practicallv similar conditions in the Mediterranean 

 basin, have graduallv acquired that physical similarity- 

 which has led Sergi to the assumption that they have a 

 proximate common ancestry, and that they accordingly 

 form but a single race. 



Nor is there any lack of instances of convergence of tyoe 

 under similar conditions in the case of the lower animals. 

 We saw that the asses of South-Western Asia aooroximate 

 in colour to the asses of North-East Africa, and in respect 

 of the size of the ears and absence of shoulder-stripe, more 

 especiallv to the nearest of these, the ass of Somaliland. 

 A'et it does not follow that they are more closely related' 

 to the Somali ass than they are to their own next neigh- 

 bours, the kiang. On the contrary, it is much more likely 

 that the Somali ass is closely related to those of Abyssinia, 

 and that the South-Western Asiatic asses are closely- 

 related to the kiang. The approximation in colour, 

 absence of shoulder-stripe, and size of the ears J^etweerr 

 the asses of Somaliland and those of South-Western .Asia 

 must rather be explained by a convergence of types under 

 the somewhat similar climatic conditions of Somaliland and' 

 the nearest parts of South-Western Asia. Again, though 



