452 KINSHIP AND ADAPTATION 



as for instance the so-callod rudimentary ovules of clematis, 

 may escape entire obliteration. Cliaracters of this sort are 

 termed vestigial. Both vestigial and correlated characters 

 imply adaptations — the one past and the other present — and 

 thus may be said to result indirectly from natural selection; 

 while even the acquired characters permitted by natural 

 selection are most hkely to survive when adajitational. Hence 

 we may conclude that the central idea of Darwinism is the 

 gradual accumulation through inheritance of slight selected 

 adaptations. 



168. Acquirement versus selection. We have seen that 

 the chief difficulty which the I^araarckianw have to face 

 comes from tlieir unproved assumption that acquired charac- 

 ters may be fixed by inheritance. The Darwinians on the 

 other hand in their efforts to avoid this difficulty have fallen 

 into others which we must now examine. Darwin tells us 

 that he made it a rule to note down every fact or criticism 

 adverse to his theory as soon as it came to his attention; for, 

 as he shrewdly observes, what is unfavorable to one's view 

 is most likely to be forgotten. With the utmost candor he 

 discussed in his writings every objection known to him. He 

 was thus his own severest critic, and since he pointed out 

 to his opponents their most effective lines of attack, there 

 rightly belongs to him a share in whatever victories they 

 gain in the cause of truth against his theory. Surely no one 

 would rejoice more genuinely than he in any better explana- 

 tion of the workings of evolution. 



Since natural selection operates only through adaptive 

 variations w(> should expect that the various systematic 

 groups of plants and animals, representing as they do the 

 surviving branches of the evolutionary tree, would be very 

 generally definable by atlaptive characters or at least tiy 

 characters which clearly imply aflaptations past or present. 

 But on the contrary it is just this sort of character which is 

 found to have least systematic value, and therefore as a 

 rule we find systematic groups most clearly defined by pe- 

 culiarities which so far as we can tell have no relation what- 

 ever to the vital needs of the organisms possessing them. In 

 tracing the supposi^d e\-(ilufi(in of rlriiial is we chose a few 



