INTRODUCTION 



IV'ATURALISTS have come to l^elieve that all of the higher 

 animals and plants have descended from simpler forms which 

 lived in the past; and that these in turn were derived from even 

 simpler ancestors. Indeed, it is possible that all animate nature 

 is the offspring of one primitive living cell which contained within 

 itself the power of giving rise to all of the plant and animal life 

 of our world. 



But although we know not how or when life originated, science 

 has Ijeen able to make known some few of the remarkable changes 

 which have come o\'er animate forms under the influences of evolu- 

 tion, and natural selection. 



Excellent examples of such changes are exhibited in the great 

 Hall of Vertebrate Fossils at the American Museum of Natural 

 History, where we may see a series of fossil skeletons which prove 

 that the horse was once a four-toed creature hardl}' larger than a 

 fox but that now it walks upon its middle toe, the side ones having 

 disappeared. Another series of fossils sliows that in Eocene times 

 tlie camel was also a little four-toed creature; but now there are but 

 two toes on each font, the side ones having disapjJeared. 



A careful study of living creatures has shown that, ^vhile off- 

 spring usually bear a close resemblance to their parents, a f(^ 

 depart wideh' from the parental types, and that some of these de- 

 partures show a strong tendency to maintain themselves, through 

 inheritance, for generation after generation. l]ut this is not all, 

 for we know that animals and plants tend to increase at a rate so 

 enormous that, should all survive, the land would soon be densely 

 covered and the ocean completely filled with living creatures. 

 This, however, is prevented by the constant competition for life. 

 Only those few that are able to concpier in the strife f(n- food and 

 space can survive, and myriads of the weak and unfit must perish. 

 Whole races have succumbed to this competition. Not one of the 



