224 Evolution and Adaptation 
on a tree become elongated in consequence of becoming 
stretched, hence has arisen the foot with the long toes char- 
acteristic of arboreal birds. 
Shore-birds, “which do not care to swim,” but must 
approach the water in order to obtain food, will be in danger 
of sinking into the mud, “but, wishing to act so that their 
body shall not fall into the liquid, they will contract the habit 
of extending and lengthening their legs.” Hence have arisen 
the stiltlike legs of shore-birds. 
These ideas were more fully elaborated in the following 
year. He added the further examples: Our dray-horses 
have arisen through the use to which they have been put, 
and the race-horse also, which has been used in a different 
way. Cultivated plants, on the contrary, are the result of the 
new environment to which they have been subjected. 
In the “ Philosophie Zoologique,” published in 1809, Lamarck 
has much more fully developed his theory. Here he combats 
strenuously the idea that species are fixed. His point of view 
may be judged by the following propositions, which he be- 
lieves can be established : — 
1. That all organized bodies of our globe are veritable 
productions of nature, which she has successively produced 
in the course of a long time. 
2. That in her progress nature began, and begins still 
every day, to produce the simplest organisms, and that she 
still produces directly the same primitive kinds of organiza- 
tions. This process has been called spontaneous generation. 
3. That the first beginning of animals and of plants takes 
place in favorable localities and under favorable circum- 
stances. An organic movement having once established 
their production, they have of necessity gradually developed 
their organs, and have become diversified in the course of 
time. 
4. That the power of growth of each part of the body 
being inherited as a consequence of the first effect of life, 
