380 BIOLOGY AND ITS MAKERS 



by his previous critical studies in botany. In the progres 

 of the work he was impressed with the differences in ani- 

 mals and the difficulty of separating one species from ai 

 other. He had occasion to observe the variations producec 

 in animals through the influence of climate, temperature, 

 moisture, elevation above the sea-level, etc. 



He observed also the effects of use and disuse upon the 

 development of organs: the exercise of an organ leading to 

 its greater development, and the disuse to its degeneration. 

 Numerous illustrations are cited by Lamarck which serve to 

 make his meaning clear. The long legs of wading birds 

 are produced and extended by stretching to keep above the 

 water; the long neck and bill of storks are produced by their 

 habit of life; the long neck of the giraffe is due to reaching 

 for foliage on trees; the web-footed birds, by spreading 

 the toes when they strike the water, have stimulated the 

 development of a membrane between the toes, etc. In the 

 reverse direction, the loss of the power of flight in the " wing- 

 less" bird of New Zealand is due to disuse of the wings; 

 while the loss of sight in the mole and in blind cave animals 

 has arisen from lack of use of eyes. 



The changes produced in animal organization in this 

 way were believed to be continued by direct inheritance and 

 improved in succeeding generations. 



He believed also in a perfecting principle, tending to 

 improve animals — a sort of conscious endeavor on the part 

 of the animal playing a part in its better development. Fi- 

 nally, he came to believe that the agencies indicated above 

 •were the factors of the evolution of life. 



His Theory of Evolution. — All that Lamarck had written 

 before he changed from botany to zoology (1794) indicates 

 his belief in the fixity of species, which was the prevailing 

 notion among naturalists of the period. Then, in 1800, we 

 find him apparently all at once expressing a contrary opinion, 



