92 ANIMAL FORMS 



the lack of food, and other agencies annihilate the larger 

 part. We also know that no two offspring are exactly 

 alike. They exhibit individual differences. One bird may 

 have a larger bill than another of the same brood which 

 excels in length of wing. As noted above, all the offspring 

 will not attain maturity. Those best adapted to their sur- 

 roundings will have the best chances of survival. The 

 increased length of bill or wing may be. slight, but it may 

 be just this amount which enables the bird to probe deeper 

 or fly farther and thus secure the requisite amount of food. 

 A premium is placed on length of wing or bill generation 

 after generation, with the result that a long-billed species 

 arises distinct from the long-winged which trace their 

 ancestry back to the same parents. It is the same prin- 

 ciple which enables the breeder to increase the swiftness 

 of the race-horse and the strength of the draft-horse, or 

 the gardener to develop from the wild rose the great num- 

 ber of widely different varieties. In the same way other 

 slight peculiarities over very many generations may en- 

 .able other forms to gradually adapt themselves to still dif- 

 ferent modes of life. Thus vast numbers of organisms 

 gradually become modified in form and complexity, and 

 are adapted to lives which insure them a comparative 

 degree of safety and less competition with other species. 



