172 HEROES OF SCIENCE. 



the simplest animals struck him to be of primary 

 importance. Hitherto, quite as many people 

 believed that the highest and most intelligent 

 animals were created first, and that the lower ones 

 had degenerated from them. Lamarck conceived 

 that nature, acting by law, commenced with the 

 simplest things, and that one species formed 

 others, so that the present animals and plants are 

 the outcome of those of the past history of the 

 earth. He believed in incessant change in nature, 

 and that when our knowledge is complete the 

 apparently well separated and defined species will 

 be found to be united by intermediate forms, and 

 cease to be species. 



Hitherto naturalists had considered kinds of 

 animals and plants, or species as they are more 

 properly called, to have been specially created as 

 they are seen by us, and that they were unalterable 

 and invariable. No one with any great knowledge 

 of animals and plants had speculated about the 

 origin of species, and the causes of the differences 

 of kinds, or had endeavoured to place all the great 

 classes of the animal kingdom in a series, main- 

 taining that they were related by descent. Right 

 or wrong in his speculations, Lamarck made an 

 epoch in zoology, by writing on the philosophy of 

 zoology, and dealing with the possible causes of 

 the different kinds of animals. He considered that 

 during all the geological ages, down to the present 

 time, animals and plants had been exposed to great 

 changes in their external conditions; changes of 



