50 THE LAW OF BIRTHS AND DEATHS 



opposite view, as we shall presently see, is the more 

 probable/' * 



It is, no doubt, probable that sterility may in some 

 measure react on the size of the fruit. But it is a neces- 

 sary deduction from the principles of organic evolution 

 that the degree of fertility shall be decided by the condi- 

 tion of the organism as a whole, and not vice versa. To 

 allow the environment to act directly on the reproductive 

 system, and through the resulting effects modify the rest 

 of the organism, would, from an evolutionary point of 

 view, be absurdly futile. This would make a species the 

 mere appendage of its reproductory system instead of 

 making the reproductory system serve the purpose of 

 maintaining the species. It is no reply to this to point 

 to the effects of castration on the rest of the organism. 

 The effects of castration are not the effects of sterility 

 resulting from the action of the environment, but are 

 the results of the loss of certain hormones caused by the 

 extirpation of the glands which produce them. Observe 

 that the fruits which are notorious for sterility are in- 

 variably propagated asexually, and consequently are not 

 selected for the production of fertile seed, but usually 

 for seedlessness. As a result the principle has full play, 

 and these fruits become more infertile in proportion as 

 they are highly cultivated. 



With plants which are cultivated for a heavy yield of 

 seed the result is directly opposite. " With respect to 

 plants, no one would expect wheat to tiller more, and 

 each ear produce more grain, in poor than in rich soil, or 

 to get in poor soil a heavy crop of peas or beans. Seeds 

 vary so much in number that it is difficult to estimate 

 them, but on comparing beds of carrots in a nursery 

 garden with wild plants, the former seemed to produce 



1 Variation of Animals and Plants under Domestication t chap, xviii. 



