SELECTED ADAPl'ATIONS 449 



offspring, and the moro often such peculiarities have appeared 

 in the line of ancestry the surer they are to reappear in all 

 the descendants. Neo-Darwinism is thus in sharpest contrast 

 with Neo-Lamarckism. The thoroughgoing Darwinian of 

 to-day rejects all direct influence of the environment as a 

 factor in organic evolution. Assume spontaneous variations, 

 he would say, and let some of them be in adaptational direc- 

 tions, then in the struggle for existence which is always going 

 on, the life and death of rivals will turn upon which has in- 

 herited the better equipment, and upon this will also depend 

 the chance of transmitting to offspring the qualities which 

 saved the parent's life. Every gain in eificiency of adaptation 

 will thus be preserved and successive gains accumulated till 

 highest efficiency is reached, and when the most perfect 

 adaptation has been secured it will be maintained indefinitely 

 so long as the environment remains essentially unchanged. 

 Since there are often different ways of attaining the same 

 end, and so fitting different individuals successfully into the 

 same enviromnent, and since also there are different environ- 

 ments to which a variable species may accommodate itself, 

 such a species may give rise to several species in the course 

 of many generations. If the intermediate forms or " connect- 

 ing hnks" from being less perfectly adapted than the extreme 

 forms should eventually succumb in the struggle, and so 

 become extinct branches of the genealogical tree, gaps would 

 appear between the surviving forms permitting us to define 

 them as cUstinct species. A longer continuation of the same 

 process would result in the differentiation of genera, families, 

 and higher groups. 



Let us see how the theory of natural selection would apply 

 to our supposed evolution of clematis. Imagine many 

 thousand primitive marsh-marigold individuals inhabiting 

 moist localities surrounded by drier spaces. These plants 

 would be sure to vary somewhat in their ability to withstand 

 occasional dry seasons. Among the millions of seeds pro- 

 duced by the tougher inchviduals a good share would surely 

 be scattered along the edge of the drier spaces where there 

 would yet be enough moisture for them to sprout. Those of 

 the seedlings which had come from the toughest parents and 



