Coloration evidence for natural selection J. Bowler wrote that Darwin's theory In his 1889 book "Darwinism", the naturalist Alfred Russel Wallace considered the white coloration of Arctic animals. He recorded that the Arctic fox, Arctic hare, ermine and ptarmigan change their colour seasonally, and gave "the obvious explanation", that it was for concealment. The modern ornithologist W. L. N. Tickell, reviewing proposed explanations of white plumage in birds, writes that in the ptarmigan "it is difficult to escape the conclusion that cryptic brown summer plumage becomes a liability in snow, and white plumage is therefore another cryptic adaptation." All the same, he notes, "in spite
Climate of the Arctic of heat from the subsurface land and ocean (both of which gain heat in summer and release it in winter) to the surface and atmosphere. Arctic days lengthen rapidly in March and April, and the sun rises higher in the sky, both bringing more solar radiation to the Arctic than in winter. During these early months of Northern Hemisphere spring most of the Arctic is still experiencing winter conditions, but with the addition of sunlight. The continued low temperatures, and the persisting white snow cover, mean that this additional energy reaching the Arctic from the sun is slow to have