586 



NATURE 



[October i i, 1900 



beisa lived side by side in the Kalahari, or Peters's palla and the 

 common species in Rhodesia, there would perhaps be strong reasons 

 for thinkinp; that the differences in the facial bands, which enable 

 us to recognise these species apart, serve the same end where the 

 antelopes are themselves concerned. But the gemsbok and the 

 beisa, the common and Angolan palla, never cross each other's 

 path. Again, in cases where the geographical areas of two 

 forms, closely allied, but distinguishable by bands or patches, 

 meet, the two forms frequently interbreed; and so falsify the 

 contention that marks keep like to like. 



That ungulates of different sorts herd together is well known ; 

 we read, for example, of zebras, gnus, pallas, spring-boks and 

 buffaloes feeding in each other's company on the veldt. But 

 so distinct from each other in form are these animals and others 

 that might occur with them, that it is rating their visual powers 

 very low — much lower, indeed, than our own — to hold that 

 they require special patches to keep them from committing the 

 errors of identification which the hypothesis assumes they are 

 liable to fall into. I believe, then, that the need for recognition 

 marks in the case of antelopes has been much over-rated,^ and 

 is too slight to warrant the belief that the facial and other stripes 

 of, say, the gemsbok or sable have been perfected by their use- 

 fulness as such. On the other hand, when we see that the 

 pattern of the zebra is for concealment, that the network of 

 white stripes on the giraffe blends with the lights passing 



Fig. 2. — A, Face of the Beisa ; b, face of the Bontebok. 



through the intercrossing branches of trees, that the colour and 

 shape of the feeding hartebeest are like those of the ant-hills, 

 all these and other facts attesting the importance of conceal- 

 ment, we are justified in suspecting that the white blaze of the 

 bontebok and the facial bands of the gazelles and oryxes are 

 developed for concealment and not for recognition. 



The markings take the form of strongly contrasted bands of 

 white and black, or brown. Objects bahded in this way are, as 

 a rule, more, and not less, difficult to see in their natural sur- 

 roundings than those that are uniformly coloured. There is 

 little of the gloss on the coat of a grey or white horse that is 

 seen on a bay or black, because white hair reflects the light less 

 vividly than dark. Hence alternating bands of these hues im- 

 part a blurred irregular aspect to a body, destroy the apparent 

 evenness of its surface and break up the continuity of its outline. 

 In an uncertain light a zebra's stripes'^ " merge into a grey tint," 

 and mutually counteract each other, so that the animal is nearly 

 invisible. 



The stripes on the head of a gemsbok or sable are in a general 

 way so like those on a zebra's coat that they must, one would 



1 If the American prong-buck were an inhabitant of Africa, I presume 

 that its conspicuous patterns, possibly indeed the unique shape of its horns, 

 would be cited as evidence supporting the theory of recognition marks. 

 Biit in the prairies of the United States there are no species that resemble 

 it in size and form, so as to create confusion as to identity. The species 

 furnishes a good instance of Thayer's principle. 



- Mr. Wallace is surely " putting the cart before the horse " in the 

 passage where he speaks of the coloration of the zebra as an instance of 

 a style of marking for recognition becoming also protective. 



NO. 1615, VOL. 62] 



think, have the effect of making the head inconspicuous. To 

 explain the prevalence of .siich marks upon the head and fore- 

 part of the body, of which t^e quagga furnishes an illustration, 

 the following suggestions may be made. 



Once aware of an enemy's presence, an antelope has three 

 chances of escape — concealment, flight and self-defence. Con- 

 cealment is often the wisest course to pursue, especially where 

 females and young are concerned. For concealment perfect 

 stillness is of all things most important. Movement means 

 detection, and detection may mean death. But it is necessary 

 at the same time for every movement of the enemy to be 

 scrutinised, so that the right moment for flying may be seized, 

 when the necessity for flight becomes apparent. For this 

 purpose the face must be turned towards the enemy and both 

 eyes be kept upon him. In this watchful attitude little of the 

 foreshortened body is visible from the enemy's point of view, 

 and if the head of the antelope be carried low with the nape in 

 a line with the spine, practically nothing of the animal is 

 exposed but the head and the fore-legs. Hence the special 

 importance of protective markings on these parts. ^ Again, 

 when lying on the ground the body will often be hidden by low 

 scrub or, if cover be absent, may simulate a mound of earth or 

 a termite's nest "^ ; but the head, if protectively coloured, may 

 with safety be raised to keep an eye on the surrounding country 

 and guard against surprise. 



The sexual colours of the Tragelaphines still remain to be 

 touched upon. Darwin believed that the markings of the 

 kudu, harnessed bush-buck, &c., were in the first instance 

 acquired by the male, then intensified by sexual selection, and 

 partially . transferred to the female. Against this hypothesis 

 may be urged the evidence already adduced in favour of their 

 protective^ value, and the distinctness they exhibit in the newly- 

 born or even foetal young. Nevertheless a difference of colour, 

 small or great, but as yet unexplained, does exist between the 

 males and females of all the species of the group. It is notice- 

 able, too, that the deviation affects the male ; that it takes the 

 direction of nigrescence, but by no means always of beauty, and 

 that the female adheres to the typical coloration of the group. 



There is no evidence, so far as I am aware, that the as- 

 sumption of a dark coat by the male is connected with any 

 peculiarity in mode of life of this sex, which would attest its use 

 for concealment. On the contrary, since the colour — at least, 

 in the case of the nylghaie {" Descent of Man," p. 535) — be- 

 comes intensified at the breeding season, without the growth 

 of new hair, and has its appearance arrested by emasculation, 

 its significance appears to be purely sexual and the outcome or 

 accompaniment of " male katabolism." If so, it may have been 

 intensified and fixed by the exercise of choice on the part of the 

 females, or by the destruction or expulsion of their paler, less 

 vigorous rivals by the stronger and darker males, which thus 

 secured the females for themselves and left the greatest number 

 of offspring. 



It is significant that the three species of antelopes, namely 

 the nyala, the nylghaie and the Indian black buck, in which the 

 sexes differ strikingly from each other — differ indeed to an 

 extent that is equalled by few species of mammals and sur- 

 passed by none — the female is without horns or other weapons 

 of defence. This defencelessness, coupled with the exigencies 

 of maternity, has compelled an adherence on her part to the 

 normal protective coloration of the group ; whereas the males, 

 powerfully built and strongly horned, have been able to dis- 

 pense to a great extent with colours that harmonise with those 

 of the environment. 



Warning characters are rare in mammals ; but the difference 

 in colour between the bull and cow of the species just mentioned 

 may conceivably benefit the former at the expense sometimes of 

 the latter by serving to distinguish him, the horned powerful 

 fighter and dangerous antagonist when brought to bay, from her, 

 the weak and defenceless one vvho may be attacked and pulled 

 down with impunity. Why not ? R. I. PococK. 



I Presumably it is for an analogous reason that the tiger has a pair oj 

 sunlight patches on its face, so that its chances of concealment may be 

 increased when watching for prey or creeping towards if. 



- In the case of the gemsbok, bei<a and some gazelles the black longi- 

 tudinal stripe passing along the side may enhance this resemblance by 

 representing the shadow that is often seen where a boulder or mound meets 

 the soil. The darkening of the coat on this area of the body, such as is 

 seen, for instance, in the Asiatic wild ass (Kiang), should have the effect of 

 deadening the light reflected from the bulging flank. 



3 Here and elsewhere in this article I have purposely used the word 

 " protective ' as the equivalent of procryptic or celative, which are less 

 familiar to geneial readers. 



