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Show 194 THE DESCENT OF MAN. PART!. of the hair on the limbs, and the course of the medullary arteries.8 It must not be supposed that the resemblances be-tween man and certain apes in the above and many other points-such as in having a naked for.ehead, long tresses on the head, &c.-are all necessarily the result of unbroken inheritance from a common progenitor thus characterised, or of subsequent reversion. Many of these resemblances are more probably due to analogous variation, which follows, as I have ~lsewhere attempted to shew, 9 from co-descended orgamsms having a similar cons~ituti~n and ~a~i~g bee~. acted on by similar causes mducmg vanab1l~ty. Y\ 1th respect to the similar direction of the han: on the for~arms of man and certain monkeys, as th1s character IS common to almost all the anthropomorphous apes, it may probably be attributed to inheritance; but not certainly so, as some very distinct American monkeys are thus characterised. The same remark is applicable to the tailless condition of man ; for the tail is absent in all the anthropomorphous apes. Nevertheless this character cannot with certainty be attributed to inheritance, as the tail, though not absent, is rudimentary in several other Old World and in some New World species, and is quite absent in several species belonging to the allied group of Lemurs. Although, as we have now seen, man has no just right to form a separate Order for his own reception, he may s On the hair in Hylobates, see 'Nat. Hist. of Mammals,' by C. L. l\iartin, 1841, p. 415. Also, Isid. Geoffroy on the American monkeys and other kinds, 'Hist. Nat. Gen.' vol. ii. 1859, p. 216, 243. Eschricht, ibid, s. 46, 55, 61. Owen, 'Anat. of Vertebrates,' vol. iii. p. 619. Wallace, 'Contributions to the Theory of Natural Selection,' 1870, p. 344. 9 'Origin of Species,' 5th edit. 1869, p. 194. 'The Variation of Animals and Plants under Domestication,' vol. ii. 1868, p. 348. .CIJAP. VI. AFFINITIES AND GENEALOGY. .1'95 perhaps claim a distinct Sub-order or Family. Prof. Huxley, in his last work/0 divides the Primates into three Sub-orders; namely, the Anthropidm with man alone, the Simiadre including monkeys of all kinds, and the Lemuridre with the diversified genera of lemurs. As far as differences in certain important points of structure -are concerned, man may no doubt rightly claim the rank of a Sub-order; and this rank is too low, if we look .chiefly to his mental faculties. Nevertheless, under a genealogical point of view it appears that this rank is too big~, and that man ought to form merely a Family, or possibly even only a Sub-family. If we imagine three lines of descent proceeding from a common source it is quite conceivable that two of them might afte; the lapse of ages be so slightly chanaed as still to • 0 remam as species of the same genus; whilst the third line might become· so greatly modified as to deserve to rank as a distinct Sub-family, Family, or even Order. But in this case it is almost certain that the third line would still retain through inheritance numerous small points of resemblance with the other -two lin~s. Here then would occur the difficulty, at ~resent msol.uble,. how much weight we ought to assign m our classificatiOns to strongly-marked differences in .some few points,-that is to the amount of modification undergone; and how much to close 1·esemblance in numerous unimportant points, as indicating the lines of descent or genealogy. The former alternative is the most obvious, and perhaps the safest, though the latter appears the most correct as giving a truly natural dassification. To form a judgment on thi& head,. with reference to man we must glance at the classification of the 10 'An Introduction to the Classification of Animals;' 1869, p. 99. 0 2 |
