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 
(Palacornis torguatus)—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 
325 
