802 ADAPTATION 



merit of an excess of color under the necessary 

 conditions. 



It is possible that other nascent intrinsic adap- 

 tations are present in different individuals, unno- 

 ticed and inconspicuous until the requisite envi- 

 ronment causes them to reach the limit of their 

 individual power, that they are environmental 

 adaptations only in appearance. On the other 

 hand, it is certain that in cave animals there is a 

 gradual bleaching vdth the removal from the 

 light. It is at first purely ontogenic. But no 

 scheme of selection ^ will account for the pro- 

 gressive reduction in the pigment in successive 

 generations. Nevertheless the color becomes less 

 in each generation. And in the final establish- 

 ment of the bleached condition in hereditary suc- 

 cession even in the light we have an instance of 

 the transmission of an environmental adaptation. 



Where environmental adaptation is the result 

 of a struggle with the physical environment, the 

 struggle is entirely independent of the rate of re- 

 production. The individual must adapt himself 

 to heat and cold whether alone or not. Temper- 

 ature and other elements of the physical environ- 

 ment affect many individuals at one and the same 

 time. For this reason the physical environment, 

 when it makes its presence felt, operates in a 

 dramatic way. It attacks the mass, sometimes 

 kilUng thousands of the non-adapted at one 

 stroke. As long as it does not kill all, the kill- 



' Mutation is ruled out without selection. 



