30 SOCIAL EVOLUTION 



of their favorable qualities to tlioir prog-eny. Some in- 

 dividuals ^vill be born with variations from the adapted 

 ancestral type which will prove of decided advantage. 

 These organisms will have a better chance to survive 

 than those that happen to vary from the ancestral type 

 in a disadvantageous direction. And so, in the course 

 of time, as the climate changes in that locality, the plastic V 

 group of living plants and animals will be modified and 

 will undergo change from their original characteristics. 

 As intermediate forms perish and new variations appear 

 giving greater advantage in ability to meet the condi- 

 tions of life, the present inhabitants will differ more and 

 more from the original inhabitants so that if we were to 

 see both side by side we should be led to think that wo 

 were observing two quite distinct forms of life instead of 

 related forms. But if we could see the intermediate 

 forms, we could reconstruct the series and understand 

 how one form was descended in almost direct line from 

 another form now quite extinct and with different struc- 

 ture and function. Although the intermediate forms 

 connecting a living group of animals with an older form 

 have long since passed from the surface of the earth, 

 naturalists are able to reconstruct the series of descent 

 with a remarkable degree of accuracy because Nature 

 has preserved for us in the form of fossils the shape and 

 mold in which these creatures were cast millions of 

 years ago. This, in brief, is Darwin's famous doctrine 

 of the origin of the species by descent under the influence 

 of natural selection. It is the core of the theory* of 

 Evolution. 



Let us now summarize the points that have been made 

 in this chapter: 



,(/) The amount of food and space upon the earth for 



