CHAPTER XV. 



The Causation of Structure — The Influence of Ante-partem Environment 

 upon Structure. 



Having now firmly grasped the fact that the structure of an 

 organism chiefly depends upon heredity, and that, compared 

 with it, any other moulding power is altogether insignificant, 

 we have now to study more particularly the part which E plays 

 in moulding the organism. 



Although its influence is infinitely less than that of 

 heredity, it is nevertheless capable of profoundly modifying 

 structure, and its effects are deserving of most careful study. 



I have endeavoured hitherto to keep the treatment of these 

 two great plastic powers as far as possible apart, for the sake 

 of clearness, but it has not been possible to succeed in this 

 entirely. 



The influence of E disturbs heredity. Were the E exactly 

 alike for every child born to the same parents, all the children 

 would be exactly alike, save, of course, for such differences as 

 depend upon sex : that is to say, the sons would exactly re- 

 semble each other, and the daughters likewise. And if the 

 world were peopled afresh from another Adam and Eve under 

 an identical E for all, all men on the one hand and all women 

 on the other, would be exactly alike at corresponding ages. 



This proposition may seem a bold one, but I shall bring forward 

 strong evidence in support of it. Should, however, the reader 

 deem this evidence inconclusive, the hypothesis will, neverthe- 

 less, be found to be a good working one. To me the conclu- 

 sion seems so tempting, that I am surprised biologists have not 

 embraced it eagerly. Perhaps some have actually done so, 

 but certainly neither Darwin nor Spencer have committed 

 themselves to it, although the latter philosopher, by implication 

 at least, would almost seem to hold the view. 



