1 84 THE MUTATION THEORY 



that prolific creator of wonderful adaptations, has so contrived that 

 directly this evolution becomes of importance as a factor in survival 

 it is brought to a standstill ; the species must wait for that rarest 

 of phenomena, an adaptive mutation. 



305. To sum up, the Mendelian doctrine the notion that 

 inheritance is alternative, that allelomorphs meet in the zygote but 

 separate in the descendant gametes is founded on experiment. 

 It has not been tested by experiment. Experimental tests reveal 

 the existence of blending when natural varieties are crossed, and 

 of latent characters when artificial varieties are crossed, and, there- 

 fore, in both cases negative the hypothesis of segregation. The 

 attempt to explain away latent traits by the hypothesis of factors 

 and determiners is founded on a pure guess which is negatived by 

 their occurrence in pure-bred varieties. The mutation hypothesis 

 can hardly even be said to be founded on experiment ; for most 

 mutations have been simply observed. In any case the notion that 

 evolution depends solely or mainly on mutations neither has, nor can 

 be tested experimentally ; for we can never be sure that we have 

 correctly reproduced ' natural ' conditions, nor can we continue our 

 experiments long enough. But both the Mendelian and Mutation 

 hypotheses may be tested by the ordinary and necessary scientific 

 procedure of making a rigorous deductive inference of consequences 

 and appealing to reality for confirmation. In neither case have 

 their supporters applied the test. Both hypotheses, therefore, are 

 " awful examples " of all that scientific thinking should not be. 



306. The reader perceives that the traits which mainly dis- 

 tinguish the experimental biological school from all other schools 

 in all other branches of science are its self-imposed restrictions in 

 observing and thinking restrictions which render it impossible for 

 the experimental worker to prove his hypotheses to the satisfaction 

 of other people, or for others to disprove them to his satisfaction. 

 With the exception of data furnished by some few human abnor- 

 malities and the like, almost the whole of the facts used have been 

 drawn from experiment, and none of them have been used to test 

 the thinking. We read occasionally in the literature of that school 

 such pronouncements as, " Evolution became the exercising ground 

 of essayists. . . . Genetic experiment was first undertaken, as we 

 have seen, in the hope that it would elucidate the problem of 

 species. . . . The time has now come when appeals for the vigorous 

 prosecution of this method should rather be based on other 

 grounds." x " The time is not ripe for the discussion of the origin 



1 Bateson, Mendel's Principles of Heredity, pp. 3-4. 



