14 ANTICIPA TION AND INTERPRETA TION OF NA TURE. 



ronment became more congenial, and the idea began 

 its unchecked development. 



If we look at the idea in itself, we first dis- 

 tinguish between the law of Evolution as an expla- 

 nation of the origin of all forms of life ; second, the 

 evidences for such a law, and third, the theories 

 and conjectures as to the natural causes or factors 

 underlying this law or constituting it. The full 

 conception came very late. Apparently Lamarck 

 was the first to grasp Evolution in its modern 

 significance, and to see the analogy between the 

 past history of life and a great widely branching 

 tree, having its roots in the simplest organisms, 

 its shorter branches in the lower, and its longer 

 branches in the higher forms of life. According 

 to this now familiar analogy, the living forms of 

 to-day are the terminal twigs of great branches 

 which represent the lines of extinct ancestors. 

 These branches united near the trunk with others, 

 whilst still other branches, with their terminal 

 branchlets, have entirely died out in past time. 

 Or, to trace the history upwards instead of down- 

 wards and begin at the roots, the lower branches 

 of the tree are comparatively few, and represent the 

 great classes of animals which divided and sub- 

 divided into orders, sub-orders, families, genera, 

 species, and so on. 



Prior to Lamarck this branching nature of de- 

 scent was only very crudely perceived. This was 

 because Aristotle's general view that the existing 



