GERMINAL SELECTION 121 



This process can, of course, no more be proved iiiatlieinatically 

 than any other biological processes. No one who is unwilling to 

 accept germinal selection can be compelled to do so, as he might be to 

 accept the Pythagorean propositions. It is not built up from beneath 

 upon axioms, but is an attempt at an explanation of a fact established 

 bj" observation — ^the disappearance of disused parts. But when once 

 the inheritance of functional modifications has been demonstrated 

 to be a fallacy, and when it has been shown that, e\en with the 

 assumption of such inheritance, the disappearance of parts which are 

 only 23asslvely useful, and of any parts whatever in sterile animal forms, 

 remains unexplained, he who rejects germinal selection must renounce 

 all attempt at explanation. It is the same as in the case of personal 

 selection. No one can demonstrate mathematically that any variation 

 possesses selection value, but whoever rejects personal selection gives 

 up hope of explaining adaptations, for these cannot be referred to 

 purely internal forces of development. 



The total disappearance of a part which has become useless takes 

 place with exceeding slowness ; the whales, which have existed as such 

 since the beginning of the tertiary period, have even now not 

 completely lost their hind-limbs, but carry them about with them 

 as rudiments in the muscular mass of the trunk, and the birds, which 

 are even older, still show in their embryonic primordia the five fingers 

 of their reptilian forefathers, although even their bird-ancestors of the 

 Jurassic period, if we may argue from Archcvopteryj;, had only three 

 fingers like our modern birds. A long series of similar examples 

 might be given, and modern embryology in particular has contributed 

 much that, like this example of birds' fingers, points to a certain 

 orderliness in the disappearance of the individual parts of an organ 

 which has become superfluous. Parts which, in the complete animal,, 

 have disappeared without leaving a trace, appear again in each 

 embryonic primordium, and disappear in the course of the ontogeny. 

 Speaking metaphorically, we might express this on the basis of the 

 determinant theory, by saying that the determinants, as they become 

 weaker, can only control an increasingly short period of the whole 

 ontogeny of the organ, so that ultimately nothing more than 

 its first beginning comes into existence. But this is only a 

 metaphor; we cannot tell what really happens as long as we are 

 ignorant of the physiological role of the determinants, and even of 

 the laws governing the degeneration of a useless organ. In respect 

 of the latter, much might still be achieved if comparative anatomy 

 and embryology were studied with this definite end in view, and 

 perhaps we should e^•en be able to draw more definite conclusions 



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