EVOLUTION 981 



An opportunity for new permutations and combinations is afforded 

 {a) in the reduction-division that occurs in the maturation of the 

 germ-cells, and {b) in the reassortment that takes place in fertilisa- 

 tion. But (c) there is strong evidence in support of the view that 

 there may be "crossing-over" or interchange between the groups 

 of paired elements or genes, as if they were arranged in double 

 file and a number on the right exchanged position with a corre- 

 sponding number on the left. Thus, as regards all kinds of novelty 

 or new departure that can be accounted for in terms of new per- 

 mutations and combinations of representative hereditary factors 

 or genes, we know more than Darwin did, who, with his characteristic 

 frankness, confessed that his ignorance of the causes of variation 

 was immense. But the probability is that, apart from the shuffling 

 of the cards, there may be from time to time an intrinsic change 

 in the nature of the gene itself. If so, that remains one of the central 

 secrets of life. 



THE BIOLOGICAL THEORY OF NURTURE 



Horoscopes are not much in fashion nowadays, except among the 

 highly imaginative or the undisciplined ; but the problem is always 

 with us as we look at a babe: What manner of person lies there, 

 in possibility ? How far is the final result already fixed, how far is 

 the outcome an open question ? Is life in some measure an unpre- 

 dictable adventure ? 



What are the factors or influences that determine the shaping of 

 an organism and its life? Man's case is in some measure peculiar, 

 since he is, more or less, a rational, social person, ^coov ttoXltlkov, as 

 Aristotle puts it ; and super-organic influences, such as social tradi- 

 tion, play upon him potently; but, biologically considered, all living 

 creatures are subject to the same laws. For all alike there are, sub 

 specie vitce, three biological "Factors" — Heredity, Function, and 

 Environment. The influence of function and environment is techni- 

 cally called "Nurture" in contrast to what is implied in the inherited 

 "Nature". 



The first Factor is Heredity — which means the relation of genetic 

 continuity between successive generations. The natural inheritance 

 includes all that the living creature is or has to start with in virtue 

 of its hereditary relation. "Bless not thyself", said Sir Thomas 

 Browne, "that thou wert born in Athens; but, among thy multi- 

 plied acknowledgments, lift up one hand to heaven that thou wert 

 born of honest parents, that modesty, humility, and veracity lay 

 in the same egg, and came into the world with thee." "A man", as 

 Heine said, "cannot be too careful in the selection of his parents." 



