EVOLUTION OF THE COLORS OF BIRDS. 23 



if the birth mean standard of an organ equal 3, and the 

 survival mean 5 when selection is operative, the standard 

 cannot possibly fall below 3 when selectioji ceases. 



Mr. J. T. Cunningham criticises pammixis as follows:* 

 " The fallacy of this argument is so obvious that it is 

 surprising it should be for a moment accepted. For 

 what is stated of the maxima variations is equally true 

 of the minima. In the absence of all selection the 

 minima variations will be combined in sexual union 

 with variations superior to themselves, and therefore in 

 each successive generation the minimum will be raised. 

 Thus the only possible result of pammixis, on Weis- 

 maun's theory of variation, will be the production of 

 uniformity in a disused or useless organ, and the de- 

 generation or disappearance of such an organ will be 

 absolutely impossible." 



In an article on "The Factors of Organic Evolution,"! 

 Prof. Geo. J. Romanes calls attention to the fact that he 

 had enunciated the principle of pammixis under the 

 name "Cessation of Selection," as early as 1873. He 

 had not claimed, however, that this cessation of selec- 

 tion could of itself produce the total disappearance of an 

 organ or part. As an instance of this, he supposes a 

 structure to have been raised from to an average of 

 100, and then to have become wholly useless, so that 

 natural selection would be no longer operative in main- 

 taining the standard. Reversal of selection would then 

 set in, due to economy of growth, and variations 101, 

 102, 103, etc., would be eliminated, while variations 99, 

 98, 97, etc.", would be favored. To continue the explana- 

 tion in the writer's own words: "For the sake of 

 definition, we shall neglect the influence of economy 



* The New Darwinism, Westminster Review, July, 1891, p. 23. 

 + Nature, XXXVI, Aug. 25, 1887, pp. 401-407. 



