io6 PIONEERS OF EVOLUTION PART 



Aristotelian mechanical figure of life as a ladder, 

 with its detached steps, he substituted the more 

 appropriate figure of a tree, as an inter-related or- 

 ganism. He argued that the course of the earth's 

 development, and also of all life upon it, was con- 

 tinuous, and not interrupted by violent revolutions. 

 In this he followed Buffon and Hutton. Buffon, 

 in his Theory of the Earth, argues that ' in order to 

 understand what had taken place in the past, or 

 what will happen in the future, we have but to 

 observe what is going on in the present.' This is 

 the keynote of modern geology. ' Life,' adds 

 Lamarck, 'is a purely physical phenomenon. All 

 its phenomena depend on mechanical, physical, and 

 chemical causes which are inherent in the nature 

 of matter itself.' He believed in a form of 

 spontaneous generation. Rejecting Buffon's theory 

 of the direct action of the surroundings as agents 

 of change in living things, he sums up the causes of 

 organic evolution in the following propositions : 



1. Life tends by its inherent forces to increase 

 the volume of each living body and of all its parts 

 up to a limit determined by its own needs. 



2. New wants in animals give rise to new move- 

 ments which produce organs. 



3. The development of these organs is in propor- 

 tion to their employment. 



4. New developments are transmitted to offspring. 

 The second and third propositions were illustrated 



by examples which have provoked ridicule. .Lamarck 

 accounts for the long neck of the giraffe by that organ 

 being continually stretched out to reach the leaves at 

 the tree-tops ; for the long tongue of the ant-eater or 



