4 THE CHARACTERS OF LIVING BEINGS 



two species are very different. He differs yet more from a plant, 

 because the germ-plasms are yet more different. One man re- 

 sembles another because all human germ-plasm is much alike, but 

 every man differs somewhat from every other, because the germ- 

 plasm contained in no two germ-cells is exactly similar. A species 

 undergoes evolution when, and only when, its germ-plasm under- 

 goes change. When, by careful breeding, we improve our domestic 

 animals and plants, the alteration is, in essence, always a germinal 

 change. 



6. It is now believed by almost every one who has an adequate 

 acquaintance with the facts that the organic world, the world of 

 plants and animals, arose by processes of evolution. Even people 

 who still deny the whole truth admit, and have always admitted, 

 a large part of it. Thus all men believe that the various branches 

 of the human species had origin in a common stem Adam and 

 Eve, heathen deities, a species of lower animals, it matters not 

 which. But human races have since diverged widely in size, 

 shape, colour, and many other traits. Moreover, the direction of 

 the change has always been such that every race has become 

 particularly well-fitted to the surroundings in which it has long 

 dwelt. Thus Englishmen flourish better in England than Negroes, 1 

 who, on the other hand, are better adapted to conditions of life 

 prevalent in West Africa. The reality of evolution, therefore, is 

 not in dispute. Only the extent of it is disputed, and only, as 

 a rule, by people whose knowledge is correspondingly limited. 



7. We need not pin our faith to the hypothesis that the 

 chromatin is the germ-plasm ; we need not even suppose that the 

 germ-plasm is contained wholly or even mainly in the nucleus. 

 Nor need we accept any theories as to the composition of it. But 

 some such substance there must be in the germ-cell, some sub- 

 stance which is the germ-plasm, the bearer of heredity ; and 

 probability points to it being the chromatin of the nucleus. 

 One very important point to which we shall have to refer again 

 and yet again should be noted. Since the offspring of the same 

 parents invariably differ more or less among themselves, it 

 follows that, though the quantitative division of the chromatin 

 is apparently exact, the qualitative division may not be so. The 

 daughter-cells may receive similar quantities ; but it is possible 

 that they do not receive exactly similar kinds of germ-plasm. 



8. The whole of the child, therefore, is derived from a single 

 cell, the fertilized ovum, which in turn was derived wholly from 



1 See 439- 



