136 THE EVOLUTION OF INSTINCT 



and fifty years tumbles even when on the ground and con- 

 tinues to do so until taken up. 



Whether or not other factors have piayed a part in the 

 evolution of behavior we shall not here discuss. Certainly 

 their claims cannot be said, at present, to rest upon a very 

 satisfactory basis. If it may savor of dogmatism to contend 

 for the all-sufficiency of natural selection, it is but an ex- 

 hibition of folly to reject as of little worth the only hypothe- 

 sis by which we can account for much of the evolution along 

 adaptive lines which has taken place. 



If we reject tho Lamarckian theory it is still possible to 

 conceive how the activities of organisms may after all have 

 a guiding influence upon the course of evolution. It is a 

 somewhat striking coincidence that three writers, J. Mark 

 Baldwin, H. F. Osborn, and C. Lloyd Morgan, put forward 

 independently, and at nearly the same time, a theory to 

 explain how this guiding influence might take place with- 

 out having recourse to the Lamarckian factor. There is 

 considerable evidence from fossil forms, the structural 

 adaptations of living organisms, and the interrelations of 

 structure and behavior, which indicates that evolution has 

 proceeded along lines corresponding to the modifications 

 produced in the individual by its own activities. There can 

 be no doubt that the adaptations acquired through these 

 activities have frequently enabled the organism to survive 

 in the struggle for existence. This power of individual ac- 

 commodation, like other characteristics of the organism, is 

 subject to a certain degree of congenital variability. It fol- 

 lows that those congenital variations which enable the organ- 

 ism to. acquire adaptive modifications with greater readiness 

 will be preserved, and consequently variations in the direc- 

 tion of these acquired modifications will accumulate. Were 

 it not for the adaptations acquired through the organism's ac- 



