THE HISTORY OF EVOLUTIONARY THOUGHT 



the gene seemed to raise formidable obstacles to the origin of new species, 

 so that genetics was regarded as a sort of blind alley at the end of which 

 stood the sign: THE GENE, DEAD END. 



A third factor was the work of Johannsen on inheritance of size in beans. 

 He found that, in a seed stock of variable inheritance, selection is highly 

 eflFective in increasing or decreasing the size of the beans. If a genetically 

 pure line is obtained, however, then selection no longer has any effect. To 

 illustrate, from a pure line with an average weight of 49.2 centigrams, he 

 selected beans weighing 20, 40, and 60 centigrams. The average weights 

 of their offspring were 45.9, 49.5, and 48.2 centigrams respectively. Plainly, 

 selection of the parents had not influenced the average weights of the 

 offspring at all. Johannsen concluded that selection could be effective only 

 in a stock with hereditary variability, but that variations produced by the 

 environment (including nutrition, sunlight, temperature, moisture, etc.) 

 were unimportant for evolution. 



An additional factor was the mutation theory of DeVries. In his studies 

 of the evening primrose, Oenothera, DeVries had discovered sudden 

 changes of considerable magnitude which behaved like Mendelian genes. 

 He called such sudden hereditary changes "mutations," and he believed 

 that some of his mutants were actually new species, produced at a single 

 step. Thus, Oenothera lamarckiana occurred suddenly in a form much 

 larger than normal, and DeVries described it as a new species, O. gigas. 

 DeVries, incidentally, was one of the codiscoverers of Mendel's work. 

 Evolution was now conceived as a series of mutations occurring in pure 

 lines. Natural selection found small place or none. 



Finally, much of the work of the Romantic Period was taxonomic in 

 character, and now taxonomy had fallen into disrepute. "Taxonomist" be- 

 came a term of reproach, and such men were regarded as merely biologi- 

 cal file clerks. Contributing to this was the fact that many taxonomists 

 were Lamarckian in their viewpoints. 



Biologists generally still believed that evolution must be a fact, but they 

 were gravely doubtful either that the main causal factors were known, 

 or that the necessary clews for their discovery were at hand. Their view- 

 point is well typified by William Bateson, who began his address before 

 the 1921 convention of the American Association for the Advancement of 

 Science with the statement that "I may seem behind the times in ask- 

 ing you to devote an hour to the old topic of evolution." Later in the 

 same address, he said that "Discussions of evolution came to an end pri- 

 marily because it was obvious that no progress was being made. . . . When 

 students of other sciences ask us what is now currently believed about the 

 origin of species, we have no clear answer to give. Faith has given place 

 to agnosticism . . . we have absolute certainty that new forms of life, new 

 orders and new species have arisen on earth. That is proven by the pale- 

 ontological record . . . our faith in evolution stands unshaken." 



This, then, was the tenor of evolutionary thinking during the Agnostic 

 Period. Bateson's speech was printed in Science in January, 1922. During 

 the year that followed. Science published only a single challenge to Bate- 

 son's position, and that was written by H. F. Osborn, an elderly zoologist 



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