CHAPTER XXIII 

 DESCENT WITH CHANGE 



Thoughtful men will find in the lowly stock whence Man has 

 sprung, the best evidence of the splendor of his capacities; and will 

 discern in his long progress through the past, a reasonable ground 

 of faith in his attainment of a nobler future. — Huxley. 



From the time of the Greek natural philosophers there always 

 have been men who have sought a naturalistic explanation of the 

 origin of the diverse forms of animals and plants, and who have 

 suggested that the present ones arose from earlier forms by a 

 long process of descent with change, or evolution. But with the 

 revival of natural history studies after the Middle Ages, the pre- 

 vailing ideas in regard to creation led the majority, perhaps al- 

 most unconsciously, to assume that there is merely a limited 

 number of kinds of organisms, all of which were created at one time. 

 And this is not so strange when one considers that nearly all of 

 the important facts which we have reviewed in the preceding 

 pages were yet to be discovered, and that the number of known 

 kinds of animals totalled but a thousand or so instead of about a 

 million as to-day. 



The pioneer work of the early Renaissance naturalists consisted 

 principally of collecting and describing animals and plants. This 

 involved making a catalog of the different kinds — classifying them 

 in some way — and consequently some basis of classification 

 was sought. Thus attention was focussed on the kinds, or 

 species, and for practical, if for no other reasons, the species as- 

 sumed a prominence which overshadowed the individuals which 

 composed it. 



Indeed, to-day biologists are hard put to it to define a species. 

 Of course everyone recognizes not only that there are many kinds 

 of animals and plants, but also that many individuals are essen- 

 tially the same. Groups may be formed of individuals which differ 

 less among themselves in the sum of their characters than they 

 do from the members of any other group of individuals. And 

 further, the members of a group produce other individuals which 



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