132 DARWINISM AND HUMAN LIFE 



changeful, and the nature of the young organism 

 may be profoundly modified by them. Thus we 

 try to distinguish and it is of enormous practical 

 as well as theoretical importance between the 

 expression of hereditary nature realised in normal 

 nurture and the individually acquired modifica- 

 tions which are due to changes or peculiarities in 

 that nurture. The characters of a newly hatched 

 chick stepping out of the imprisoning egg-shell are 

 in the main strictly hereditary ; but they need not 

 be altogether so, for during the three weeks before 

 hatching there has been some opportunity for 

 peculiarities in the environment to leave their 

 mark on the developing creature. Still more is 

 this the case with the typical mammalian embryo, 

 which develops often for many months as a sort of 

 internal parasite within the mother, in a complex 

 and variable environment. And as life goes on, 

 peculiarities due to nurture continue to be super- 

 imposed on the hereditary qualities, especially 

 when the creature trades with time, and, by choosing 

 its own nurture, creates for itself an individuality. 

 (4) The Idea of the Continuity of Generations. 

 Another step is the general acceptance of a 

 somewhat subtle and yet essentially simple idea, 

 , which may be called the continuity of genera- 

 ' tions. 1 There is a sense, Galton says, in which 

 the child is as old as the parent, for when the 

 ', parent's body is developing from the fertilised 

 \ ovum a residue of unaltered germinal material is 



1 In his address " Fifty Years of Darwinism," Prof. Poulton says : 

 " The greatest change in evolutionary thought since the publication 

 of the ' Origin ' was wrought, after Darwin's death, by the appear- 

 ance of that wonderful and beautiful theory of heredity, which 

 looks on parents as the elder brother and sister of their children." 



