PDF - Wallace Online

366 TROPICAL NATUREmale to special developments of dermal appendages and colour,quite independently of sexual or any other form of selection."Thus the hump on the male zebu cattle of India, the tailof fat-tailed rams, the arched outline of the forehead in themales of several breeds of sheep, and the mane, the long hairson the hind legs, and the dewlap of the male of the Berbura"goatare all adduced by Mr. Darwin as instances of characterspeculiar to the male, yet not derived from any parentancestral form. Among domestic pigeons the character ofthe different breeds is often most strongly manifested in themale birds ;the wattles of the carriers and the eye- wattles ofthe barbs are largest in the males, and male pouters distendtheir crops to a much greater extent than do the females,while the cock fantails often have a greater number of tailfeathersthan the females. There are also some varieties ofpigeons of which the males are striped or spotted with black,while the females are never so spotted (Animals and Plantsunder Domestication,i.161) ; yet in the parent stock of thesepigeons there are no differences between the sexes either ofplumage or colour, and artificial selection has not been appliedto produce them.The greater intensity of coloration in the male, which maybe termed the normal sexual difference, would be furtherdeveloped by the combats of the males for the possession ofthe females. The most vigorous and energetic usually beingable to rear most offspring, intensity of colour, ifdependenton, or correlated with vigour, would tend to increase. Butas differences of colour depend upon minute chemical orstructural differences in the organism, increasing vigour actingunequally on different portions of the integument, and oftenproducing at the same time abnormal developments of hair,horns, scales, feathers, etc., would almost necessarily lead alsoto variable distribution of colour, and thus to the productionof new tints and markings. These acquired colours would,as Mr. Darwin has shown, be transmitted to both sexes orto one only, according as they first appeared at an early age,or in adults of one sex ;and thus we may account for someof the most marked differences in this respect. With theexception of butterflies, the sexes are almost alike in thegreat majority of insects. The same is the case in mammals