ORGANIC EVOLUTION — DAVENPORT 427 



About 40 per cent of the birds had a white pluma«;e, 40 per cent a 

 black (or nearly bhick) plumage, and 20 per cent a phnna<;c in pen- 

 ciled or striped markinixs, more or less like that of the ordinary 

 game or the jungle fuAvl. Of these the crows killed 24. Expecta- 

 tion, on the basis of random attack on the birds, was that about 9.G 

 would bo white, 9.G black, and 5 penciled. Actually there were 

 killed 10 white, 13 black or prevailingly so, and 1 coarsely mottled 

 gray and buff. No truly penciled bird was killed. This observation 

 tends to illustrate the principle that the self-colors in wild birds 

 tenil to be eliminated because conspicuous to their enemies; birds 

 with mixed pattern are relatively imnnme from attack because rela- 

 tively inconspicuous. 



Now, though it has not been experimentally proven, yet the hy- 

 pothesis may be entertained, that the presence of light-colored mice 

 in limestone regions and of dark-colored mice on lava beds may result 

 from an elimination of mutations that are in disharmony w^ith the 

 background. To nocturnal predaceous animals, like the owls which 

 catch mice, a white or light-yellow mouse on a black lava bed would 

 be seen and captured before a black one. 



One further fact must be taken into account in considering the ad- 

 justment of organisms to their environment, and that is that change 

 of environment may well cause and apparently has in the past often 

 caused the elimination of species over the whole extent of their area 

 of destruction. 



Consider how widespread must have been the consequences on the 

 fauna of the Northern Hemisphere as far south as Long Island and 

 even further south of the great ice sheets that covered the circum- 

 polar territory in glacial epochs. Many poorly clad species of mam- 

 mals must have found the icy conditions insupportable; just as the 

 mastodon and mammoth did. The change in environment may be 

 of a more subtle sort. Thus the great size and herd instincts of the 

 bison enabled it to develop enormously on the extensive plains of 

 North America and rendered it more than a match for the Amerinds 

 living in a stone age. Just this size and number wholly unfitted 

 these mammals for the new environment of the aggressive agricul- 

 turally inclined white man armed with a rifle. Agriculture and free- 

 ranging bisons could not coexist, and the rifle eliminated the 

 mammals. So to-day the great size and aggressiveness of the large 

 mammals of Africa are a challenge to the sportsman, and the future 

 seems to spell extinction for them. Here we have to do with elimin- 

 ation resulting from what may be called a cultural evolutionary 

 " mutation " — the rifle. 



But man's part in evolution is not merely in the elimination of his 

 large enemies, which he has all too thoroughly mastered, but in his 

 struggle witli the small and innumerable insects that threaten his 



