Panmixia and the Principle of Economy 191 



The addition suggested by Romanes that the tendency 

 to atavistic reversion favors minus variations at the ' 

 expense of plus variations, does not suffice. 151 For in 

 the first place an atavistic reversion could appear at best 

 only in the phyletic characters acquired last, and in the 

 second place, after the first stages of atrophy had ap- 

 peared it would in any case tend from that time on to 

 insure the preponderance of plus over minus variations. 



One could nevertheless assert that panmixia is not 

 necessary for Weismann's theory. The principle of the 

 economy of the organism by which every useless and 

 unused organ is harmful because it withdraws nourish- 

 ment from other organs is by itself enough, if one 

 rejects the inheritance of acquired characters, to explain 

 the gradual phyletic disappearance of useless parts. 



But this hypothesis is easily refuted by some calcula- 

 tions of Spencer, showing that it is impossible that the 

 advantage to the organism of a small inborn and fortu- 

 itous minus variation in the useless organ, particularly 

 when this is already very much degenerated as is for 

 instance the hind leg of the whale, can procure for the 

 individual an advantage over others and so provoke the 

 phylogenetic passage to a yet greater atrophy. And no 

 great value can be attributed to the counter observation, 

 which Weismann several times repeats, that we are still 

 quite unable to measure the selective efficacy of the 

 struggle for existence. One need think only of the 

 parasites and particularly of the endoparasites, which 

 have always an excess of nutrition and in which there- 

 fore the advantage of the degeneration of useless organs 

 would become reduced absolutely to zero. And it is 



lB1 Romanes : A Note on Panmixia. Contemporary Review. Octo- 

 ber 1893. P. 612. 



