From Lamarck came about the same time his _Researches_, and a little
later his _Zoological Philosophy_, which introduced a new factor into
the process of evolution--the action of the animal itself in its
efforts toward a development to suit new needs--and he gave as his
principal conclusions the following:
1. Life tends to increase the volume of each living body and of all
its parts up to a limit determined by its own necessities.
2. New wants in animals give rise to new organs.
3. The development of these organs is in proportion to their employment.
4. New developments may be transmitted to offspring.
His well-known examples to illustrate these views, such as that of
successive generations of giraffes lengthening their necks by
stretching them to gather high-growing foliage, and of successive
generations of kangaroos lengthening and strengthening their hind
legs by the necessity of keeping themselves erect while jumping,
provoked laughter, but the very comicality of these illustrations
aided to fasten his main conclusion in men's memories.
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