390 FOUNDATIONS OF BIOLOGY 



advance that from this period on it is not possible, even in 

 the most general survey, to discuss the development of biol- 

 ogy as a whole. The composite picture must be formed by 

 emphasizing and piecing together various lines of work, such 

 as taxonomy, comparative anatomy of animals, embry- 

 ology, physiology of plants and animals, genetics, and evolu- 

 tion. 



1. Taxonomy 



Taxonomy has as its object the bringing together of or- 

 ganisms which are alike and the separating of those which are 

 unlike; a problem of no mean proportions when a conserva- 

 tive estimate to-day shows upward of a million species of 

 animals and plants leaving out of account the myriads 

 of forms represented only by fossil remains. 



Naturally the earliest classifications were utilitarian or 

 more or less physiological, but as knowledge increased em- 

 phasis was shifted to the anatomical criterion of specific dif- 

 ferences, and thenceforth classification became an important 

 aspect of natural history a central thread both practical 

 and theoretical. Practical, in that it involved the arranging 

 of living forms so that a working catalog was made which 

 required nice anatomical discrimination, and therefore the 

 amassing of a large body of facts concerning animals and 

 plants. Theoretical, because in this process botanists and 

 zoologists were impressed, almost unconsciously at first, with 

 the 'affinity' of various types of animals and plants, and so 

 were led to problems of their origin. 



From Aristotle, who emphasized the grouping of organisms 

 on the basis of structural similarities, we must pass over some 

 seventeen centuries, in which the only work of interest was 

 done by the herbalists and encyclopaedists, to the time of 

 RAY (1628-1705) of England and LINNAEUS (1707-1778) of 

 Sweden. Previous to Ray the term species was used some- 



