EVOLUTION OF BIRDS, 1b 
modified forms, is accepted by most naturalists. As 
originally presented, it assumed that the continued exist- 
ence of any animal depended upon its adaptation to its 
manner of life. Among a large number of individuals 
there is much variation in size, form, and color. Some 
of these variations might prove favorable, others unfa- 
vorable. Those which were favorable would give to the 
individual possessing them an advantage over its fellows, 
and, by what is termed WVatural Selection, it would be 
preserved and its favorable characters transmitted to its 
descendants. But the less fortunate individuals, which 
lacked the favorable variation, would be handicapped in 
the race for life and be less likely to survive. 
Without necessarily opposing this theory, the follow- 
ers of Darwin’s predecessor, Lamarck, attach more im- 
portance to the direct action of environment on the ani- 
mal—that is, the influence of climate, food, and habit. 
The effect of the first two I will speak of in treating of 
color; the last we may usc to illustrate the difference in 
these two theories by asking the question, “Is habit due 
to structure, or is structure the result of habit?” Has 
Nature, acting through natural selection, preserved those 
variations which would best fit a bird to occupy its 
place in the world, and are its habits the outcome of 
the characters thus acquired, or have the changes which 
during the ages have occurred in a bird’s home, forcing 
it to alter its habits, been followed by some consequent 
change in structure, the result of use or of disuse? For 
my part, I answer “ Yes” to both questions, and turn to 
our stiff-tailed, spear-tongued Woodpecker to explain 
my reply. I can readily understand how the shape of 
these tail-feathers is the result of habit, for the same or 
similar structure exists among many birds having no 
close relationship to one another, but all of which agree 
in their peculiar use of the tail as a prop; the Creep- 
