36 SOCIAL EVOLUTION 



The answer is found in the selective influence of environ- 

 ment. There is an endless diversity of environments. 

 Tlie iceberg-, tlie hot spring, the mountain top, the abysses 

 of the ocean, the interior of another creature, all con- 

 stitute a complex of changing influences. "In many cases 

 where the external changes are regularly recurrent like 

 the seasons and the tides, the organism falls into step 

 with them so that there are internal rhythms." To some 

 of these changes the living organism is able to adjust 

 itself temi)()rarily. To others the response is not so 

 delicate, and the novel conditions provoke structural 

 changes from which the organism never recovers, the 

 limits of organic elasticity having been passed. Adapta.- 

 1io7i is the key-note of organic nature, and it is exactly 

 the tiling natural selection seenres. However modified, 

 those individuals which are not adapted to their environ- 

 ment are destroyed in the struggle for existence, leaving 

 only the well-adapted forms alive. The environment 

 molds the living organism. Those whose innate plas- 

 ticity is equal to the occasion are modified and survive. 

 Those whose plasticity is not equal to the occasion are 

 exterminated. This modification takes place generation 

 after generation, but, as such, is not inherited. But any 

 variations aiising in the germ cells which are similar 

 in direction to these modifications, will tend to support 

 them, and to favor the organism in which they occur. 

 Thus plastic modification leads, and germinal variation 

 (variations arising in the germ cells) follows; the one 

 paving the way for the other. The modification is not 

 inherited, but it establishes a condition under which con- 

 genital variations ^" are given time to get a hold on the 



10 Congenital variations arc variations which arise in the germ cell. 

 Thev are variations which are inherited. Tliev are not modifications. 



