108 THE PRINCIPLES OF HEREDITY 



if, in the future, as modern socialistic tendencies seem to 

 indicate, the labourer receives not according to the result 

 achieved, but according to the labour expended, if the weak 

 in muscle and brain survive and have offspring equally with 

 the strong, very slow regression will follow, no doubt ; unless 

 indeed, in an era more enlightened than our own, Artificial 

 Selection takes up the task which Natural Selection has laid 

 down, and, by a careful selection of parents, raises mankind to 

 a pinnacle of strength and intelligence as yet undreamed of. 



173. Nevertheless, though it may be true that Man's evo- 

 lution on the ancestral lines is nearing its term, it is not true 

 that he has ceased to evolve altogether. The direction of 

 his evolution has changed, but the speed of it has not slack- 

 ened. On the contrary, it is probably greater to-day than at 

 any former period of his life-history. Biologists, who are 

 occupied chiefly with visible physical characters or with 

 mental traits, have not noted this change of direction ; but it 

 is none the less real. The study of it lies within the special 

 province of the medical man. 



174. If human evolution has ceased, if Natural Selection 

 no longer eliminates the unfit among civilized peoples, it is 

 evident that most people must die of old age, or else that the 

 elimination is not selective. But, as a fact, millions of people 

 perish, even in England which is highly civilized, before or 

 during the child-bearing age, nearly all of whom are elimin- 

 ated because they are constitutionally incapable of surviving 

 under the ordinary conditions of the environment in which 

 they find themselves. 



175. If we wish to ascertain the direction in which any 

 species is evolving, it is a good plan to note which members 

 of it survive and which perish. We shall thus, by observing 

 the difference in qualities between the fit and unfit, be able 

 to discover which traits favour survival, and, therefore, which 

 traits are undergoing evolution by the accumulation of inborn 

 variations. As a rule, it is impossible to apply this method 

 to plants and animals " in a state of nature." We do not 

 know enough about them. A dead bird or insect, or a 

 withered shrub in the thicket does not give us sufficient 

 information. It may have perished through the agency of 

 any one of a hundred different causes, to which an unascer- 

 tainable deficiency in any one of a hundred different qualities 

 may have exposed it. Or its death may have been due to 

 pure mischance. The great majority of plants and animals 

 are destroyed before reaching maturity. Only the fit survive, 

 and, even of the fit, only a small minority. The adaptation 



