j I BEREDITY AND SEX 



questioD of how the higher animals and plants, and 

 man himself, arose from the lower forms seemed the 

 chief goal of biolo^cal work and thought. The out- 

 come was i" establish the theory of evolution. The 

 circumstantial evidence that was gathered seemed so 

 fully in accord with the theory of evolution that the 

 theory became widely accepted. The acute stage was 

 passed, and biologists found themselves in a position 

 to examine with less haste and heat many other phe- 

 nomena of the living world equally as important as 

 evolution. 



It gradually became clear, when the clouds of con- 

 troversy had passed, that what I have ventured to call 

 the "circumstantial evidence" on which the theory of 

 evolution so largely rested, would not suffice as a direct 

 proof of evolution. Investigation began to turn once 

 more to that field of observation where Darwin had 

 found his inspiration. The causes of variations and 

 the modes of inheritance of these variations, the very 

 foundations of the theory of evolution, were again 

 studied in the same spirit in which Darwin himself had 

 Mudied them. The return to Darwin's method rather 

 than to Darwin's opinions marks the beginning of the 

 new era. 



In 1900 three botanists were studying the problem 

 of heredity. Each obtained evidence of the sort 

 -Mendel had found. Happily, Mendel's paper was 

 remembered. The significance of his discovery now 

 became apparent. De Vries, Correns, and Tschermak 

 brought forward their evidence in the same year (1900). 

 Which of the three first found Mendel cannot be stated, 

 and is of less importance than the fact that they ap- 



