28 SEXUAL DIMORPHISM 



Morgan has already pointed out, there is no physiological 

 reason why the growth of feathers should be connected with 

 the proximity of main arteries and nerves. We have no 

 reason to suppose that the large supply of blood for the 

 pectoral muscles overflows into the skin and causes the 

 feathers of the breast to sprout luxuriantly as does the grass 

 round a spring of water. And, moreover, if it were so, the 

 special plumes ought to be equally developed in the females, 

 and indeed all birds ought to possess plumes on the breast 

 similar to those of the male bird of paradise, since in all the 

 position of the nerves and blood-vessels is the same. 



In so far as it attributes the evolution of secondary sexual 

 peculiarities to supposed general physiological principles, and 

 not to selection from indefinite individual variations, Wallace's 

 explanation resembles these views of evolution which are 

 distinguished as Lamarckian. This is only one out of several 

 subjects on which Mr. Wallace is Lamarckian without 

 knowing it, and apparently in spite of himself. Although he 

 independently invented the theory of natural selection he 

 does not admit the action of that principle in the case of 

 the mental and moral characteristics of man, or of a special 

 kind of selection in relation to sex. Not that Mr. Wallace 

 has ever acknowledged himself to be a Lamarckian. He 

 probably has a strong prejudice against the epithet, but that 

 may be because, like many others, he has to some extent 

 misunderstood the position of the Lamarckians, and has not 

 realised the similarity between his own views and theirs. 



The views which I am about to support are also of the 

 kind called Lamarckian, but they are by no means the same 

 as those of Mr. Wallace on the subject under consideration. 

 I attribute the evolution of secondary sexual characters to 

 alleged physiological principles of growth and modification, 

 but these principles are quite different from those suggested 

 by Mr. Wallace, and I believe they are principles founded on 



