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. 
