HISTORICAL ACCOUNT OF EVOLUTION THEORY 31 
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, but 
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 structure. 
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 eyesin 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 thé germ 
plasm.’”? The whole theory has come to be known as the “germ-plasm 
