PDF - Wallace Online

172 NATURAL SELECTION vm. ^ditions in which it is placed. But it will now be a differentcreature. It will be not only swifter and stronger, and morefurr ity will also probably have changed in colour, in form,perhaps have acquired a longer tail, or differently shapedears ;for it is an ascertained fact that when one part of ananimal is modified, some other parts almost always change,as it were in sympathy with it. Mr. Darwin calls this" correlation of growth," and gives as instances that hairlessdogs have imperfect teeth white; cats, when blue-eyed, aredeaf ;small feet accompany short beaks in pigeons and other;equally interesting cases.Grant, therefore, the premises : 1st, That peculiarities ofevery kind are more or less hereditary; 2d, That the offspringof every animal vary more or less in all parts of theirorganisation ; 3d, That the universe in which these animalslive is not absolutely invariable ;none of which propositionscan be denied ;and then consider that the animals inany country (those at least which are not dying out) must ateach successive period be brought into harmony with thesurrounding conditions and we;have all the elements for achange of form and structure in the animals, keeping exactpace with changes of whatever nature in the surroundinguniverse. Such changes must be slow, for the changes in theuniverse are very slow ;but just as these slow changes becomeimportant, when we look at results after long periodsof action, as we do when we perceive the alterations of theearth's surface during geological epochs, so the parallelchanges in animal form become more and more striking, inproportion as the time they have been going on is great as;we see when we compare our living animals with thosewhich we disentomb from each successively older geologicalformation.This is, briefly, the theory of natural selection, whichexplains the changes in the organic world as being parallelwith, and in part dependent on, those in the inorganic. Whatwe now have to inquire is, Can this theory be applied inany way to the question of the origin of the races of man 1 oris there anything in human nature that takes him out of thecategory of those organic existences over whose successivemutations it has had such powerful sway?