236 DEVELOPMENT AND HEREDITY. 



of some change of stimulus seems to cause a lack of 

 development and growth. We can imagine a num- 

 ber of individuals reproducing asexually, forming a 

 variety so highly specialised and completely adapted 

 to certain limited local conditions that a compara- 

 tively slight change of the conditions might cause 

 the total destruction of the variety. The ill effects 

 of too great a degree of specialisation are well 

 known. On the other hand, a sexual mixture with 

 individuals living under slightly different conditions 

 — that is, a commingling of different developmental 

 potentialities — seems to give a greater power of 

 adapting to changes of environment. Each individ- 

 ual, instead of inheriting, so to speak, the experience 

 of a single straight line of ancestors, inherits from a 

 geometrical progression of ancestors almost the whole 

 experience of his race, and comes into the world 

 equipped with an hereditary impulse capable of re- 

 sponding to all the conditions under which any one 

 of his race can survive. Sexual reproduction thus 

 appears in a new light, as a means of widening the 

 range of responsive power by combining a great 

 number of inherited potentialities, and so enabling 

 the developing organism to cope with any of the 

 various conditions which have been met by its 

 numerous ancestors. 



