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 payed 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 the 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- 
