Wallace's Theory Criticised 



Entwicklungsmechanik der Organismen, vol. 

 xxvi., p. 378), namely, that the secondary 

 sexual characters in those species which possess 

 them show an entire absence of uniformity in 

 nature and position. " Why," asks Cunningham, 

 ' 'should the male constitution of the stag show 

 itself in bony excrescences of the skull, in the 

 peacock in excessive growth of the other end of 

 the body ? Why should the larynx be modified 

 in one mammal, the teeth in another, the nose in 

 another ? Why is the male newt distinguished 

 by a dorsal fin, the male frog by a swelling on 

 the fore foot ? " 



Another objection to the explanation of sexual 

 dimorphism suggested by Wallace, is that in 

 many species of bird, as, for example, the house 

 sparrow and the green paroquets of India, the 

 external differences between the sexes are so 

 slight that it is unreasonable to believe that they 

 are the result of natural selection. It seems 

 impossible to hold that the Rose-ringed Paroquet 

 (Palaeornis torquatus) a species which nests in 

 holes would have become extinct if the hens had 

 developed the narrow rose-coloured collar that 

 characterises the cocks. 



Darwin pointed out that while Wallace's 

 hypothesis might appear plausible if applied to 

 colour, it can scarcely be said to explain the 

 origin of such structures as the musical apparatus 

 of certain male insects, or the larger size of the 



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