October 



900J 



NATURE 



585 



patches on the rump or any other visible external feature, in- 

 cluding large ears, may, if required, serve as marks of identity ; 

 but in the case of the Tragelaphines, at least, it is hard to believe 

 that that is any more their primary function than it is the 

 primary function of large ears. 



A mass of evidence can be brought forward in favour of 

 Wallace's view that the body-stripes of these antelopes are 

 protective ; but there appear to me to be equally strong reasons 

 for classifying the face and foot markings in the same category, 

 and for regarding them as representing spots or streaks of sun- 

 light passing through foliage or reflected from leaves. 



It is possible, perhaps probable, that the other white patches 

 on a typical Tragelaphine serve the same end ; but their 

 situation forcibly suggests that they have a still deeper signifi- 

 cance. I believe they come within the scope of Thayer's 

 hypothesis of concealment by the counteraction of light and 

 shade. A convex body stands out amid surroundings of its own 

 colour on account of the contrast between the light that is re- 

 flected from its upper surface and the shadow that pervades it 

 below. Take away the light by darkening the upper side and the 

 shadow by lightening the lower, and the body will vanish from 

 sight with the destruction of its visible shape. By applying this 

 principle to a typically marked Tragelaphine, the lesser kudu for 

 example, it will be seen that the white is laid on where shadows 

 are thrown ; that the white rim on the upper lip and the white 

 chin must counteract the shadows caused by the fold of the 



Fig. I.— T?e Lesser Kudu, f, . 



mouth and by the muzzle ; the two white blotches on the neck 

 must counteract the shadows thrown by the head and by the 

 curvature of the throat, and the shadows cast by the breast and 

 groin must he similarly obliterated by the white patches on the 

 inner side of the base of the limbs. 



That the white patches must have the effect here assigned to 

 them will be obvious, I think, to any one who, with Thayer's 

 hypothesis in mind, looks at a lesser kudu when it is standing 

 full face. The reason for the presence of marks concealing the 

 animal from this point of view will be referred to later on. 



If the markings of the Tragelaphines have the significance here 

 attached to them, they should be better developed in the species 

 that live in the bush than in those that frequent the open. Let 

 us see in a few cases to what extent they are correlated with 

 habit. Two well-marked species of eland live in Africa, to wit, 

 Derby's eland ( T. derbianus) from Senegambia and the com- 

 moner form ( T.oryK) which, with its subspecies, ranges throughout 

 the whole of East and South A frica. The former, according to 

 Winwood Reade, "lives in the forest, and never of its own 

 accord enters the plain." It is reddish in colour, with a black 

 neck, a white collar, eye-stripes and many white stripes on the 

 flanks and hind-quarters. Of the common eland the typical " dun 

 coloured" desert form is, according to Selous, "particularly 

 plentiful in the dry desert country through which the Chobe runs," 

 and e.vamples " from the Kalahari desert have no sign of a 



NO. 1615, VOL. 62 ] 



stripe." Farther to the north, both in Angola, South east and 

 East Africa, this unmarked type is replaced by its ancestral form, 

 Livingstone's eland, which in colour and habits is intermediate 

 between the Cape and Senegambian species. The skin is 

 always marked with narrow white stripes, and the V-shaped 

 mark between the eyes is often present. In British East 

 Africa this eland, according to Jackson, was found in " sparsely 

 timbered country and open bush bordering the plain rather 

 than the plains themselves," and in Angola (Pentice) " it seems 

 most partial to a thinly limbered country." There is thus a 

 complete gradation from the strongly marked forest species 

 through the weakly marked species frequenting the open bush 

 to the unmarked desert species. 



Take again the kudus. Both the species are well marked 

 with white stripes on body and head, but the smaller (i". imberbis) 

 is much more strikingly marked than the larger (.S". strepsiceros), 

 having more stripes on the body and two patches on the 

 throat. In Somaliland, where both species occur, the larger 

 lives, according to Swayne, in the mountains, on very broken 

 ground where there is plenty of bush ; and sometimes indeed 

 ventures into the open plain (Inverarity). The lesser kudu, on 

 the contrary, "is found in thick jungles . . . especially where 

 there is an undergrowth of the slender pointed aloe which 

 grows from four to six feet high " (Swayne). Both Swayne 

 and Inverarity, moreover, bear witness that this species will 

 allow a hunter to get within a few yards before dashing 

 away— a notorious habit with protectively coloured animals. 

 Evidence of a like kind is furnished by other species of 

 Tragelaphines. The beautifully marked nyala {T. angasi) 

 and bongo ( T. euryceros) live in dense thickets ; and the 

 lovely little bush-bucks (7". sylvaticus, scripUis, &c.) seldom 

 venture out of cover except at night-time to feed. On the 

 other hand, the nylghaie, an aberrant member of the same 

 tribe, is without body-stripes, and lives for the most part in 

 more or less open country in India, and is not a typical 

 denizen of the thick jungle at all.^ 



Further evidence on this head is supplied by another set of 

 facts. Ungulates which live in thickets or rough ground afford- 

 ing cover to enemies have larger ears and a keener sense of 

 hearing than those of the plains or high mountains where in- 

 truders have little chance of concealment. Note the small ears 

 of the camel, a typically desert form ; or of goats and sheep 

 which from the mountain peaks cdn sweep the surrounding 

 country for miles with their eyes and seek safety in flight long 

 before the foe gets within ear shot. Compare also the small 

 equine ears of Burchell's zebra, which herds in the open plain 

 free from obstacles to interfere with vision, with the longer 

 asinine ears of the mountain zebra which frequents rocky broken 

 ground well fitted for the hiding of carnivores. In all the 

 brilliantly marked Tragelaphines the ears are long and expanded, 

 I but in the nylghaie, and especially in the common eland, they are 

 short and narrower. Indeed, one of the chief structural differ- 

 ences between Derby's eland and the Cape species is found in 

 the size of the ears.^ 



The co-existence of white marks with long ears and a bush- 

 life bears out the supposition that ihe marks, like the ears, are 

 primarily for protection, and that if subservient to purposes of 

 recognition they are merely of secondary importance in that 

 capacity. 



I strongly suspect, too, that the markings of the sable, roan, 

 gemsbok and bontebok are for concealment, and not for recogni- 

 tion as Mr. Wallace supposes. The theory of recognition 

 marks as applied to these antelopes assu ues the need of some 

 patch or spot to enable the members of a species to identify 

 their own kind amongst the herds of other sorts living in the 

 same place. The theory would rest upon a securer basis, if it 

 could be shown that closely allied species feed together. But 

 nothing, I suppose, is more certain than that, as a very general, 

 perhaps invariable, rule, closely allied and similar species are 

 not found together. If, for example, the gemsbok and the 



1 An apparent exception to the rule that the development of white stripes 

 and spots is correlated with a jungle life is found in the Sitatunga and 

 Speke's marsh-buck, which " live in vast reed beds and papyrus swamps, and 

 only come into the open at night " (Selous). Yet the stripes fade away in 

 the adults of both sexes. Why is this? Possibly because these animals 

 depend for concealment, not so much upon coloration that harmonises with 

 that of the vegetation, as upon .-» newly acquired and tfficient habit of 

 hiding under the water itself, with only the end of the nose jutting above 

 the surface (Selous and Ged^e). 



^ Compare in this connection the small ears of the orang with the large 

 ears of the chimpanzee. The former lives a more arboreal and therefore 

 safer life than the lattc, which requires quick hearing to enable it to escape 

 (O th^ trees when feeding on the ground. 



