CONSTANCY AND ADAPTATION 103 



natural selection, tlirough amphimixis, will favour the variation 

 by efEecting the adaptation of an ever greater number of indi- 

 viduals to it ; if, on the other hand, the variation be one which 

 cannot result in readaptation, then either the symmetrical curve 

 will have to be re-established (extermination of the variation), 

 or the species will continue to follow the asymmetrical curve 

 (extermination of the species). 



Thus, one of the most important efEects of amphimixis is the 

 consolidation of the constitution of the species ; for the asym- 

 metrical curve is the exception, and the symmetrical curve is the 

 rule. One of the chief reasons, therefore, for the continuous per- 

 sistence of amphimixis is that it secures the greater constancy 

 of a species, and at the same time facilitates its readaptation to 

 changed conditions. ^^ 



It must not be supposed — though the belief is very general — 

 that there is an antithesis between constancy and adaptation. 

 The constancy of a species is secured by amphimixis, as is shown, 

 for instance, in the case of the wild plant transported to a new 

 environment — that of cultivation. Amphimixis secures con- 

 stancy by eliminating a number of variations which would other- 

 wise prejudicially afEect the species, and by enabling the species 

 as a whole to resist small changes of environment. On the other 

 hand, without amphimixis it would be impossible to secure so 

 general an adaptation to greatly changed conditions — an adapta- 

 tion which is in the interest of the species itself, and without which 

 it would be eliminated. In each case amphimixis ensures the 

 continuity of the life of the species; and is an indispensable 

 factor in the struggle for existence. 



It is essential to consider amphimixis in the light of its two main 

 efEects, not only maintaining the constancy of the species, but also 

 increasing its adaptability ; both of these efEects being necessary 

 corollaries of the raison d'etre of amphimixis as an instrument for 

 the conservation of the species. The probable advantage of 

 amphimixis, as Weismann remarks, lies, for the individual, in the 



