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Show 388 GENERAL SUMMARY PArt'l' II. fications, especially through the study of monstrosities: hence the labours of experimentalists, such as those of M. Camilic Darcstc, arc full of promise for the futuro. In tho arcater number of cases we can only say that the b . cause of each slight variation and· of each monstrosity lies much more in the nature or constitution of the organism, than in tho nature of the surrounding conditions ; though new and changed conditions certahlly play an important part in exciting organic changes of all kinds. 'l'hrongh the means just specified, aided perhaps by others as yet uncliscovcr cl, man has been rai eel to his present state. But since he attained to the rank of manhood, he has divergerl into distinct races, or as they may be more appropriately called sub-species. Some of these, for instance the Negro and European, are so distinct that, if specimm1s had been brought to a naturali. t without auy further information, they would undoubtedly have been considered by him as good and true species. Nevertheless all the races agree in so many unimportant details of structure and in so many mental peculiarities, tbat those can be accounted for only through inheritance from a common progenitor; and a progenitor thus charactm·ised would probably have deserved to rank as man. It must not be supposed that tho divergence of each race from the other rae'S, and of all the races fi·om a common stock, cau be traced back to any one pair of progenitors. On the contrary, at every stage in the process of modification, all the indi vicluals which were in any way best fitted for their conditions of life, though in different degrees, would have survived in greater numbers than the less well fitted. The process would have been like that followed by man, when he does not intentionally select particular individuals, Cu..1.r. XXI. AND CONCLUDING REMARKS. 389 but breeds from all the snperior and neglects all the inferior individuals. He thus slowly but surely modifies his stock, and unconsciously forms a new strain. So with respect to modifications, acquired independently of selection, a:ticl due to variations arising from the nature of the organism and the action of the surroundirw conditions, or from changed habits of life, no sinrrle p~ir will have been modified in a much greater cle:ree than tho other pairs which inhabit the same co~ntry, for all will have been continually blended through free intercrossing. By considering the embryological structure of man, -the homologies which he presents with the lower animals,-the rudiments which he retains,-and the reversions to which he is liable, we can partly recall in imaO'ination the former con<lition of our early progenitm~; and can approximately place them in their proper position in the zoological series. vVe thus learn that man is descended from a hairy quadruped, furnished with a tail and pointed ears, probably arboreal in its habits, and an inhabitant of the Old W oriel. This creature, if its whole structure had been examined by a naturalist, would have been classed amongst the Quaclrumana, as surely as wonld the common and still more ancient progenitor of the Old and New World monkeys. The Quadrumana and all the higher z:nammals are probably derived from an ancient marsupial animal, and this through a long line of diversified forms, either from some l'eptile-like or some amphibianlike creature, and this again from some fish-like animal. In the dim obscurity of tbe past we can see that the early progenitor of all the Vertebrata must have been an aquatic animal, provided with branchire, with the t\YO sexes united in the same individual, and with the most important organs of the body (such as the brain and |