EVOLUTION 507 



ished; and that the derivation of new species is thus 

 accounted for in a simple and logical manner. By con- 

 tinual reaching for tender leaves on high branches, the 

 long neck of the giraffe was gradually produced, the slight 

 gain in length in one generation being transmitted by 

 inheritance to the next, and so on. 



The main thesis of Lamarck, as stated by himself, is 

 as follows: 



"In animals and plants, whenever the conditions of 

 habitat, exposure, climate, nutrition, mode of life, et 

 cetera, are modified, the characters of size, shape, relations 

 between parts, coloration, consistency, and, in animals, 

 agility and industry, are modified proportionately." 



As illustrating the direct effect of environment on organ- 

 isms, Lamarck chose a plant, the water-buttercup (Ran- 

 unculus aquatilis) , which may grow in marshy places, or im- 

 mersed in water. When immersed, the leaves are all finely 

 divided, but when not immersed, they are merely lobed. 



While plants are more passive, and are affected by their 

 surroundings directly, through changes in nutrition, light, 

 gravity, and so on, animals react to environmental changes 

 in a more positive and less passive manner. Thus, in 

 the words of Lamarck: 1 



"Important changes in conditions bring about impor- 

 tant changes in the animals' needs, and changes in their 

 needs bring about changes in their actions. If the new 

 needs become constant or durable, the animals acquire 

 new habits. . . . Whenever new conditions, becoming 

 constant, impart new habits, to a race of animals . . . 

 these habitual actions lead to the use of a certain part in 



1 Translated from his Philosophic Zoologique, vol. I, pp. 227, 223, 224, 

 248. 



