HISTORICAL ACCOUNT OF EVOLUTION THEORY 3 1 



what are known as overspecializations. The theory therefore would, 

 if well founded, account not only for the initial stages of new adaptive 

 characters, but also for overspecializations, two phenomena that 

 natural selection was unable to account for. Not only were pro- 

 gressive evolutionary changes explained by germinal selection, bu< 

 regressive changes seemed to be even more readily accounted for on 

 this basis. In the struggle among determiners in the germ cell 

 some of the less favored units would be handicapped at the outset by 

 insufficient food or unfavorable position and would produce smaller or 

 less effective structures. Progressively, from generation to generation, 

 these weakened determiners would lose ground and become less and 

 less successful in competition until they were weaklings among 

 determiners and would be able to initiate only degenerate or vestigial 

 structures, or else would die out and lose their place altogether, thus 

 accounting for total losses of structures. 



This theory does not exclude natural selection, but rather increases 

 its importance, for every structure that arises to the threshold of 

 utility or disutility meets the winnowing process of natural selection. 

 The fitter individuals survive in the long run and these perpetuate the 

 germ cells in which the successful determiners reside. 



A slightly different explanation of degenerating structures in- 

 volves the principle of "panmixia. " According to this idea, changing 

 environmental conditions may render certain adaptive organs of 

 lessened value or of no value, as would be the case in the eyes of cave 

 animals. In different individuals the eye determiners would vary in 

 their success in competition with other determiners, and since natural 

 selection would no longer put a premium on perfect eyes, all grades of 

 eyes would be equally inherited and gradually the poorer or degenerate 

 eyes would become more numerous, till finally there would be no 

 good eyes in the race. Thus it will be seen that the germinal-selection 

 theory was auxiliary to natural selection and tended to support the 

 latter at two of its weakest points. But the supporting theory itself 

 has the fundamental weakness of lacking a factual basis. It is purely 

 hypothetical and cannot be put to an experimental test. Every 

 time an objection to the theory was raised an auxiliary hypothesis 

 was added to explain away the difficulty, till finally it fell to the ground 

 through sheer top-heaviness, unable further to support its intricate 

 structure of interrelated hypotheses. 



A much more valuable and lasting contribution of Weismann was 

 his theory of "germinal continuity" and of the "apartness of the germ 

 plasm. " The whole theory has come to be known as the " germ-plasm 



