SELECTION 445 



possible, but, as we are dealing with one of the most im- 

 portant of biological theories, with the question of the direc- 

 tive factors in evolution, we may cite from a previous dis- 

 cussion two simple observations which illustrate discriminate 

 elimination picturesquely (Thomson, Darwinism and Human 

 Life, 1911). Prof. C. B. Davenport, of the Carnegie In- 

 stitution for Experimental Evolution, had 300 chickens in 

 a field, eighty per cent, white or black and conspicuous, 

 twenty per cent, spotted and inconspicuous. In a short time 

 twenty-four were killed by crows, and it was interesting to 

 observe that only one of the killed was spotted. The elimi- 

 nation seemed to be discriminate, and in wild conditions it 

 would doubtless have led to the elimination of the conspicu- 

 ous variants. It will be understood that we are not attach- 

 ing great importance to any individual case, such as this, 

 for criticism and corroboration are required all round; we 

 are giving an illustration merely. 



In a heavy snowstorm at Johannesburg in August, 1909, 

 many hundreds of trees were destroyed by the weight of 

 snow on the branches. In many places the roads were blocked 

 by the fallen trees. It was interesting, after the storm, to 

 notice that the elimination was in a marked degree dis- 

 criminate. The trees that suffered most were the imported 

 Australian trees, such as the Blue Gums and Black Wattles, 

 quickly growing, with soft wood, and with abundant foliage 

 that caught the snow. On the other hand, the Deodars from 

 the Himalaya mountains, constitutionally adapted to let the 

 snow slide from their pendulous branches and acicular leaves, 

 had hardly a twig broken. 



(2) In the second place, the position of the selection 

 theory has been strengthened by a recognition of its mani- 

 foldness. It takes several different forms, the logic of which 



