BIOLOGICAL EVOLUTION 73 
The knowledge and use of the Mendelian law by animal 
breeders and horticulturists during the past few years have shown 
its great importance to man in the process of active material 
adaptation, and its present use in studies of defectiveness has 
demonstrated its value in eugenics which comes under the division 
of active social adaptation. 
Before summing up the contributions of biology to sociology 
and to the subject of this book in particular it may not be amiss to 
consider briefly the position of biologists today on some of the 
fundamental questions brought out in our survey of the theories 
of Darwin and his successors. For this purpose the Centennial 
Addresses in Honor of Charles Darwin before the American 
Association for the Advancement of Science, should furnish 
impartial material. 
That inborn variation and natural selection alone are sufficient 
was questioned by J. M. Coulter of the University of Chicago 
from the side of botany. David Starr Jordan of Leland Stanford 
emphasized isolation as a factor of equal importance with natural 
selection. E. B. Wilson of Columbia showed that experiments 
had proven the possibility of the transmission of ontogenetic 
variations and gave assent to the theory of metabolism through 
chemical action. ‘“‘ Experiment,” he said, ‘‘ has established the 
fact that certain forms of development are thus controlled by 
substances, the ‘ hormones,’ that may be extracted from the 
cells that produce them, and upon injection into the body call 
forth their characteristic results. Such an effect, for instance, is 
the development of the cock’s comb in the hen upon injection of 
testic-extract and its recession to the characteristic female condi- 
tion upon cessation of the injections.” ! Professor Wilson made 
another statement of great suggestive value in its bearing on social 
progress: ‘‘ We must not forget that some of the most acute and 
thoughtful of naturalists have in recent years expressed the 
conviction that the ultimate control of development is not to be 
sought in the physico-chemical properties of the germ cells, but 
in an indwelling ‘entelechy’ or ‘ élan de la vie,’ a power of 
1 Fifty Years of Darwinism, pp. 106, 107. 
