THEORIES OF LAMARCK AND DARWIN 385 
strain and to survive. As another illustration, Darwin 
pointed out that natural sclection had produced a long-legged 
race of prairie wolves, while the timber wolves, which have 
less occasion for running, are short-legged. 
We can also see the operation of natural selection in the 
production of the sharp eyes of birds of prey. Let us con- 
sider the way in which the eyes of the hawk have been per- 
fected by evolution. Natural selection compels the eye to 
come up to a certain standard. Those hawks that are born 
with weak or defective vision cannot cope with the conditions 
under which they get their food. The sharp-eyed forms 
would be the first to discern their prey, and the most sure in 
seizing upon it. Therefore, those with defective vision or 
with vision that falls below the standard will be at a very 
great disadvantage. The sharp-evcd forms will be preserved 
by a selective process. Nature sclects, we may say, the 
keener-eyed birds of prey for survival, and it is easy to see 
that this process of natural selection would establish and 
maintain a standard of vision. 
But natural selection tends merely to adapt animals to 
their surroundings, and does not always operate in the direc- 
tion of increasing the efficiency of the organ. We take an- 
other illustration to show how Darwin explains the origin of 
races of short-winged beetles on certain oceanic islands. 
Madeira and other islands, as Kerguelen island of the Indian 
Ocean, are among the most windy places in the world. The 
strong-winged beetles, being accustomed to disport them- 
selves in the air, would be carried out to sea by the sudden 
and violent gales which sweep over those islands, while the 
weaker-winged forms would be left to perpetuate their kind. 
Thus, generation after generation, the strong-winged beetles 
would be eliminated by a process of natural selection, and 
there would be left a race of short-winged beetles derived 
from long-winged ancestors. In this case the organs are 
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