42 A Century of Science 



through a series of differentiations, and the result 

 is a change from homogeneity to heterogeneity. 

 Such was Baer's conclusion, to which scanty jus- 

 tice is done by such a brief statement. As all 

 know, his work marked an epoch in the study 

 of embryology ; for to mark the successive differ- 

 entiations in the embryos of a thousand animals 

 was to write a thousand life histories upon correct 

 principles. 



Here it was that Mr. Spencer started. As a 

 young man, he was chiefly interested in the study 

 of political government and in history so far as it 

 helps the study of politics. A philosophical student 

 of such subjects must naturally seek for a theory 

 of evolution. If I may cite my own experience, it 

 was largely the absorbing and overmastering pas- 

 sion for the study of history that first led me to 

 study evolution in order to obtain a correct method. 

 When one has frequent occasion to refer to the 

 political and social progress of the human race, 

 one likes to know what one is talking about. Mr. 

 Spencer needed a theory of progress. He could 

 see that the civilized part of mankind has under- 

 gone some change from a bestial, unsocial, per- 

 petually fighting stage of savagery into a partially 

 peaceful and comparatively humane and social 

 stage, and that we may reasonably hope that the 



