2 INTRODUCTION TO EVOLUTION 



ence gained with older models how to improve and modify their product 

 so that later models are different from, and on the whole better than, 

 earlier ones. But the later models are not literally the offspring of the 

 earlier ones. Contrariwise, it is exactly this ancestor-descendant relation- 

 ship which is visualized in the term ''organic evolution." More recent ani- 

 mals are thought of as the direct genetic descendants of somewhat differ- 

 ing ancestors which formerly lived on the earth. 



The reader will have noted that the definition of organic evolution just 

 given differs from the popular conceptions of the meaning of evolution. If 

 the proverbial "man in the street" is asked the meaning of the word, he is 

 likely to reply, "Man came from monkeys." This exclusive preoccupation 

 with man is perhaps natural in one but little acquainted with, or interested 

 in, the remainder of the living world. To a biologist the evolution of man is 

 but one portion of the vast drama of evolutionary change including all liv- 

 ing things. Each animal alive today is the product of long evolutionary 

 history. 



Another shortcoming of the man in the street's definition lies in the fact 

 that he pictures one modern form as descended from another modern 

 form. Man and monkey are contemporaries, both products of long evolu- 

 tion. It is as incongruous to speak of one as the descendant of the other 

 as it would be to speak of one member of the sophomore class in college as 

 the descendant of another member of that class. What, then, is the evolu- 

 tionary interpretation of the relationship existing between monkey and 

 man? Rather than being a father-to-son relationship, it is more compara- 

 ble to a cousin-to-cousin relationship. You and your cousin have a pair 

 of grandparents in common. Modern man and modern monkey are thought 

 of as having shared a common ancestor in the distant past. From this 

 common ancestor both inherited some characteristics in which they still 

 resemble each other. Was this common ancestor a man or a monkey? 

 Neither. He was a form that had the potentialities of giving rise to a mon- 

 key, on the one hand, or of giving rise to a man, on the other. There is no 

 evidence that any of the animals we know as monkeys have that po- 

 tentiality. 



Beginnings of the Evolution Idea 



Many people seem to think that the whole idea of evolution started with 

 a man named Darwin. This belief probably arose from the fact that Dar- 

 win's great book, The Origin of Species, published in 1859, was the first 

 widely read book on evolution published in English. This classic in our 



