REBIRTH AND HEREDITY 129 



and it would be impossible for us to adapt ourselves to the 

 new requirements that the further advancement of the world 

 will call forth. We would remain only a hereditary reproduc- 

 tion of our ancestors fitted only for the occupations they per- 

 formed. This is why whenever a species or nation becomes 

 sedentary, and loses the stimulant to competition given by 

 locomotion it stops short in its progression. This is largely 

 emphasised in evolution, so that in plant life we find that 

 the power of hereditary reproduction is much less subject 

 to variation than in animal life so far as future resemblance, 

 form, shape and continuation of the species are con- 

 cerned, and there being no motion, variation is but slightly 

 needed ; but in animals and man, species and families vary so 

 much in form and mental characteristics that the family like- 

 ness is but slight. But on the other hand, in animal existence 

 motion makes variation nearly as powerful, and in some cases 

 far more visible and marked a force than hereditary develop- 

 ment if less fixed or permanent, and in the evolution of mind 

 this is more marked than in the body. 



Thus families may vary at times perceptibly, and may 

 jump from one extreme to another. For it is a fact that 

 both mentally and physically the tendency of heredity under 

 certain circumstances is inclined to produce extremes in 

 breeding, which makes it difficult to distinguish the heredi- 

 tary result from the variation. This is most notice- 

 able when we have resort to incestuous breeding, the result of 

 which form of breeding is to produce extremes of very marked 

 types and lasting heredity. But this is only obtained at the 

 cost of the maximum amount of variation during the next 

 three or four generations. Thus the perfect type we wish 

 to obtain is arrived at by the first two or three generations 

 producing an extreme of the type we do not require, that is 

 of culls, after which the permanent type is evolved in a most 

 fixed and marked degree, and the percentage of culls drops 

 to a minimum. War has been the greatest means of such 

 culling in the past. In the same way the plant continues 

 hereditary shape much longer than the animal existence. 

 An oak leaf is an oak leaf in all places and under all condi- 

 tions of soil fit for its growth and cultivation, and shows but 

 little variation in form or shape as compared with the varia- 

 tion of animal shapes under altered conditions. Whereas 



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