AMPHIMIXIS CHECKS USELESS VARIATIONS 99 



importance for the species in the struggle for existence. But we 

 have seen that the determinants of the germ-plasm of every 

 individual are variable ; that perturbations of the intragerminal 

 nutrition are perpetually causing a " shifting of the balance " in 

 the interior of the germ-plasm ; that such minimal variations 

 caused by nutritive oscillations can progress until selection value 

 is attained — that is to say, until they attain to sufficient im- 

 portance to influence the life of the individual. Unless natural 

 selection then intervenes, the individual, which has come to be 

 out of harmony with its environment, is exterminated. It is 

 true that many of the variations thus caused by nutritive per- 

 turbations are checked by intragerminal influences before they 

 attain biological value ; but many others are not thus checked, 

 and must be a danger to the species, if not checked by selection. 

 And as such variations are perpetually arising, selection must 

 be perpetually ready to check them. 



Let us take a species which is adapted to certain conditions, 

 and suppose no amphimixis to occur. Adaptation is the result 

 of the harmony of a great number of characteristics with sur- 

 rounding conditions ; and variations of one or more of these 

 characteristics, in numerous members of the species, must in- 

 evitably be of frequent occurrence. Amphimixis, by the constant 

 mingling of different ids and the constant renewal of the germ- 

 plasm which ensues, is able to keep these spontaneous variations 

 in check ; if no amphimixis occtured, then every such variation 

 would necessarily attain biological value, and the species could 

 only be maintained by the destruction of the individuals possess- 

 ing these variations. But such destruction would soon cause the 

 normal number of the species to dwindle ; or else the whole 

 species would, little by little, vary so greatly in the majority of 

 its individuals that it woidd fall a victim to this want of harmony 

 with its environment. Excessive variation would be, without 

 amphimixis, an uncontrollable factor in the extermination of 

 species ; but through amphimixis intragerminal variations can 



7—2 



