404 OUTLINES OF EVOLUTIONARY BIOLOGY 



environment (as in the case of the potato beetle as demonstrated 

 by Tower), but that they probably also arise from the mingling 

 of different streams of ancestral tendencies in the process of 

 amphimixis or conjugation of gametes, and possibly in yet other 

 ways with which we are not acquainted. 



Of course, natural selection can only influence a species 

 through variations which are capable of being inherited, and it 

 is, as everyone knows, urged by many modern writers that 

 somatogenic variations, due either to the direct action of the 

 environment or to the use and disuse of parts, cannot be 

 inherited and therefore have no significance in evolution, and 

 that natural selection must content herself with such fortuitous 

 and non-adaptive variations as may happen to arise in the germ 

 plasm. This indeed seems an extreme view, and it is just 

 here that the split between the extreme selectionists, who have 

 gone far beyond Charles Darwin in this matter, and the followers 

 of Lamarck arises. The curious thing about the controversy is 

 that there is no inherent incompatibility between the views of 

 the two schools. The theory of the inheritance, to a limited 

 extent, of acquired characters, indeed, appears to be just what is 

 necessary to supply the deficiencies of that of natural selection. 



To say that acquired characters cannot be inherited because 

 we cannot see them being inherited in our own brief lifetimes 1 is 

 like saying that a glacier does not move because we do not see it 

 or feel it moving as we walk over it. I have endeavoured to 

 show in an earlier chapter that it is not difficult to imagine a 

 mechanism by which somatogenic characters may gradually be 

 converted into blastogenic ones, and if this is in any way 

 possible there is no reason why we should deny the possibility 

 of their inheritance. No one, however, would be rash enough 

 to suppose that all that an animal or plant acquires in its 

 individual lifetime is transmitted to its heirs. Nature imposes 

 a heavy death duty and takes away by far the greater part of the 

 capital which has been accumulated by each individual. We 

 may suppose, however, that a fraction remains, however 

 unrecognizable by our limited powers, and that these 

 fractions, accumulating under the same influences throughout 

 thousands of generations, ultimately confer upon the organism 

 as a birthright that adaptation which is essential to its existence. 



1 As a matter of fact, it appears from recent experiments that in some cases we 

 can see them being inherited (vide p. 182). 



