Tnjlaencc of Environment iqwn the Orfjanism. 4G9 



a cause, both direct and indirect, of modifications of struc- 

 ture. Sexual reproduction also caused frequent and fortuit- 

 ous variations. Tlie result of mixtures of constitutional 

 proclivities were mostly suppressed, but sometimes increased 

 by survival of the fittest. Natural selection became the 

 predominant factor in relation to fortuitous variations of 

 structure, of no account in converse with the medium, of 

 much account in the struggle with enemies and competitors. 

 Especially with plants and passive animals the survival of 

 fit variations must all along have been the chief cause of the 

 divergence of species and the occasional production of higher 

 ones. Gradually the inheritance of those modifications of 

 structure, caused by modifications of function, becomes more 

 and more important." A synthesis of all the positions is 

 thus again outlined, differing from the view expressed in the 

 Leader article of thirty-four years previously in even more 

 definite insistence on environmental influence, and in the 

 recognition of the struggle for existence, differing, too, from 

 his intermediate contributions in a marked tendency to limit 

 the importance of the struggle, i.e., of natural selection. 



A general view of the factors of evolution is still being 

 evolved, and it is premature to speak of final form. Yet 

 this much seems certain, that no attempt to explain the 

 adaptation of the organism to its environment can be com- 

 plete without a recognition that external influences in the 

 widest sense, and in various degrees of directness, have and 

 have had an important transforming and adaptive action. 

 To place this opinion in its proper perspective in relation to 

 organismal and functional variations, or in reference to 

 natural selection and other alleged conditions of progress, 

 will remain impossible until a greater wealth of experimental 

 fact makes it possible to say with security what the environ- 

 ment can or cannot do. The main object of this paper, based, 

 as I must again gratefully acknowledge, on Semper's classic 

 work, has simply been to present anew a balance-sheet of 

 representative facts and opinions in regard to environmental 

 influence. 



