THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 227 



certainty, as we can do in the case of the rudimentary organs, but 

 even on general considerations we might expect that among the 

 incipient variations of the determinants of the germ-plasm there 

 would be some which were in an ascending direction, and that among 

 these there would be some which, advanced by germinal selection, 

 would go on ascending until they attained selection value. Wieder- 

 sheim reckons, for instance, the gradually increasing differentiation of 

 the cortical zone of the human brain among the parts which are still 

 in process of ascending variation, and he is probably right in 

 doing so. 



But if variations, so slow as to be unnoticeable, are still of 

 abundant occurrence in Man, we have no reason to doubt that similar 

 processes are going on in other animals ; among the higher Vertebrates 

 at least there is hardly a species which does not exhibit regressive 

 variations even now, and in many cases progressive variations also 

 are occurring, although we cannot give definite proofs of this. 



The appearance of fixity which most species have is, therefore, 

 illusory ; in reality thej^ exhibit a slow flux, gradually setting aside 

 the superfluities they received from their ancestors, perfecting 

 the important parts to more precise adaptation and greater 

 functional capacity, and at the same time endeavouring to maintain 

 all the parts in constant harmony. We can understand that as long 

 as this process of gradual perfecting goes on, amphimixis will not 

 readily be given up. Those that retain it must always, in the long 

 run, have the preference. Moreover, as we have seen, it cannot be 

 given u.p, when it has existed through seons, because of the power of 

 persistence which the germ-plasm has gradually acquired in the 

 course of such a long hereditary succession. It could only be given 

 up if an advantage decisive as to survival were associated with its 

 abandonment, such as can be actually recognized in most cases of 

 parthenogenesis, among animals at least. 



In my opinion this indirect effect of amphimixis, that is, the 

 increasing of the possibilities of adaptation by new combinations of 

 individual variational tendencies, is the main one, while the direct 

 nutritive effect of the two germ-eells upon one another is quite 

 subsidiary. In tliis opinion I find myself in opposition to the views 

 of many if not most naturalists, who assume that amphimixis has 

 a direct, sometimes, indeed, only a direct effect, and believe that they 

 can prove it by facts. 



In support of this position it has been pointed out that allogamy, 

 that is, the mingling of individuals of different ancestry, occurs 

 even among lowly unicellulars, and then higher up among most 



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