June i6, 192 i] 



NATURE 



4S7 



Letters to the Editor. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

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 taken of anonymous communications.] 



Human and Other Tails. 



In Nature of February 24 last, p. 845, there 

 appears a report of Prof. Arthur Keith's remarks at 

 the meeting of the Royal Anthropological Institute 

 held on February 8. It may be that the Journal of 

 the institute will contain a more detailed paper on 

 the same subject, and that the fuller paper will some- 

 what modify the dicta put forward in the report as 

 it appears in Nature. But in the absence of any 

 further details it seems worth while to note some 

 of the points raised by Prof. Keith which appear open 

 to criticism. 



My right to criticise may perhaps be sustained by 

 the reference on p. 846 to Tarsius and to my pub- 

 lished views concerning its systematic position. Prof. 

 Keith's rather far-reaching generalisations were called 

 forth by the examination of one of those fleshy sacral 

 appendages commonly known as human tails. It is 

 obvious from every sentence in the article cited that 

 Prof. Keith believes that the human tail was lost 

 because man became an orthograde — that is, 

 adopted a vertical instead of a horizontal poise for his 

 body. No doubt that is a very well justified position 

 to take up, and, in so far as a human orthograde poise 

 implies a cessation of tail utility, I entirely agree with 

 him. But when Prof. Keith savs, "With the evolu- 

 tion of the upright posture the pelvic muscles which 

 act on the tail had to bear the steady burden of the 

 abdominal viscera— had to be in action as long as 

 the orthograde posture was maintained. They could 

 not serve in the support of the viscera and the move- 

 ments of the tail at the same time," I dissent from 

 him altogether. Indeed, to me it seems a remarkable 

 thing that one who is in constant association with 

 the rnuseum of John Hunter could possibly believe 

 that,^ if this dual duty of support of viscera and pro- 

 duction of tail movements were thrust upon them, the 

 muscles would fail in one respect or the other. We 

 need, as a matter of fact, go no further afield than 

 the kangaroo to see how an animal which is tvpicallv 

 orthograde may support its abdominal viscera in the 

 upright posture, and vet possess a tail which is one 

 of the most wonderful of muscularly controlled caudal 

 appendages met with among the mammals. 



Man has not lost his tail because the caudal mus- 

 culature is incapable of undertaking the dual rdle of 

 visceral support and caudal mobility. He has lost it 

 because it has ceased to be of any use to him. For 

 the same reason the gibbon, the orang, the chim- 

 panzee, and the gorilla have lost theirs. For the same 

 reason certain "pronograde apes " (which Prof. Keith 

 appears to assume possess uniformly "basal or 

 pelvic," as well as "free or terminal," portions of 

 their tails') have lost theirs. Cynopithecus possesses 

 no more than a button, the Barbarv ape still less, 

 and, indeed, the reduction of the tail is seen to the 

 best advantage in the most typically pronograde group 

 (the baboons) of the Primates. Because the tail has 

 ceased to be of any functional use certain of the lemurs 

 have also lost it, and so have a host of other mam- 

 malian forms belonging to other orders. Did it not 

 aopear flippant, one might ask if Prof. Keith imagines 

 the guinea-pig lost its tail because its caudal muscula- 

 ture could not fulfil a dual rdle. Recession of the 

 tail has been effected, and prehensile tails have been 



NO. 2694, VOL. 107] 



developed, over and over again in the mammalian 

 phylum. But one may not argue phylogeny, or the 

 limits of the possibilities of muscular adaptation, to 

 account for these things. No argument which bases 

 the loss of the tail on the grounds cited by Prof. Keith 

 carries the least conviction or bears any interpretation 

 which may be distorted into human phylogeny. 



Prof. Keith further goes on to state that "in 

 pronograde apes the pelvic visceral musculature is 

 attached to the peculiar chevron-like bones (haemal 

 arches) placed beneath the pelvic vertebrae of the tail ; 

 the reappearance of the haemal arches in the human 

 embryo during the second and third months of develop- 

 ment may be regarded as definite proof that man 

 comes of a pronograde ancestry." This is a common 

 type of argument, one that has been current far too 

 long, and one against which I have been attempting 

 to teach for some time past. Apart from the con- 

 fusion that may be caused by identifying "haemal 

 arches" with definite "chevron bones" is the gross 

 fallacy involved in the argument that because haemal 

 arches are present in pronograde apes and in man, 

 therefore man is developed from a pronograde ape. 

 Haemal arches are a primitive vertebrate heritage, but 

 they are no more ; they have no more to do with 

 the pronograde poise per se than have the neural 

 arches or the gill bars. We all know that the prono- 

 grade habit is typical of lower vertebrates, and we 

 need not quibble about a pronograde vertebrate an- 

 cestry for man. But to argue that the pronograde 

 simian ancestry of man is evidenced in the "re- 

 appearance of the haemal arches in the human embryo 

 during the second and third months of development " 

 is sheer nonsense. Haemal arches are developed in 

 birds, and one would have as good justification for 

 saying that this proved that man descended from a 

 volant ancestor as Prof. Keith has, bv the parallel 

 argument, for claiming man's descent from a simian 

 pronograde ancestor. Both arguments are fallacious 

 and stupid. 



Whilst the whole trend of Prof. Keith's remarks 

 appears to be directed towards a vindication of the 

 pronograde simian ancestry of man, he seems, in the 

 end, to disagree with the ancestral position of " Tarsius 

 spectrum, for which Prof. Wood Jones claims a special 

 human relationship." Yet of this animal he says: 

 "... in its tail and tail-musculature Tarsius is a pure 

 pronograde Primate." I should be sorry to destroy 

 the last bridge by which Prof. Keith's views might 

 be reconciled with my own ; but I have no hesitation 

 in saying that Tarsius is certainly not a pure prono- 

 grade, and that, moreover, no living animal the habits 

 of which are open to observation should be judged as 

 a pronograde by an examination of the musculature 

 of its tail. F. Wood Jones. 



The University, Adelaide, South Australia, 

 April 10. 



Twenty-five years ago it was my privilege to teach 

 Prof. Wood Jones ; he now repays me with interest 

 and with some degree of vigour. The matter wherein 

 we differ has a very direct interest, not only for those 

 who are seeking to unravel the history and relation- 

 ships of man by means of anatomical evidence, but 

 also for evejv zoologist who relies on structural details 

 for arrangPng animals in a natural or evolutionary 

 series. In man and in the four anthropoid apes-^ 

 the gorilla, chimpanzee, orang, and gibbon — the tail 

 has undergone a peculiar transformation — a sacralisa- 

 tion it may be named — for its vertebrae have become a 

 mere submerged appendix of the sacrum. The de- 

 pressor muscles of the tail have become spread out 

 to form a muscular hammock on which the pelvic 



