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 orgahisms 
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. 
