INTRODUCTION 9 



strengthened and developed. Likewise, without use it was weak- 

 ened. The supposed inheritance of these acquired characters 

 was the basis of the production of the numerous species. 



The term species was first applied to animals and plants by 

 John Ray (1628-1705) who used it to refer to a group of organ- 

 isms with similar characteristics and which freely intercrossed. 

 Many of the experiments of this period dealt with the question 

 of species. 



The Doctrine of the Constancy of Species. Linnaeus (1707- 

 1778) adopted a more strict definition although he was not always 

 consistent in his use of the word. The doctrine adopted was that 

 of the separate creation of fixed entities which were called species. 

 Lamarck denied this theory and outlined his evolutionary 

 hypothesis. Most naturalists of this period believed in the 

 immutability of species. 



It is thought that the work of Lyell (1797-1875), an eminent 

 geologist, had a marked effect on that of Charles Darwin, who was 

 his intimate friend. Lyell insisted upon the continuity of the 

 earth's history and the uniformity of agencies which wrought 

 such profound changes upon the earth. This theory was in 

 opposition to that of Cuvier, who believed that the earth's history 

 was a series of times of destruction followed by periods of tran- 

 quillity ("catastrophism"). After each such destructive period 

 it was believed that new .creation took place. 



Darwin's Theory of Natural Selection. The most influential 

 worker in the history of development of the evolutionary con- 

 ception was Charles Darwin. He and Alfred Russel Wallace 

 independently developed a theory for the origin of species and 

 united in presenting a preliminary paper in 1858. 



The publication of Darwin's " Origin of Species" in 1859 

 gradually brought about a belief in evolution. The work of Lyell 

 had helped materially to develop a belief in the orderly progress 

 of the world and assisted in preparing the way for the masterly 

 presentation of Darwin. Darwin presented such a mass of 

 evidence from widely different fields .that the entire thinking 

 world was compelled to accept evolution as a fact. The evidence 

 was grouped under such headings as organic relationship, com- 

 parative anatomy, embryology, paleontology, and domestication. 



The fact of evolution is indisputable. The explanation 

 is even yet not entirely satisfactory. Darwin's theory is founded 

 upon a series of facts as follows: 



