alike. In fact, we can find differences even between twins. Dees this varia- 

 tion continue, for any species, in any particular direction? Is there steady 

 improvement or steady deterioration? Does any species, in the course of time, 

 show more and more or less and less of any particular trait? If the actual 

 forms of life come to difler as time goes on, the process must be very slow. For 

 we do not observe such changes in a lifetime, nor have we any records of sev- 

 eral thousand years of human history to answer these questions with assurance. 



Certain evidences, however, leave no doubt that there formerly ex- 

 isted species which no longer exist: these are the fossils. And there is reason 

 to believe that at various periods in the past the plant and animal species of 

 today did not exist at all. What is the connection between the species of the 

 present and the utterly different species of the past? Or did each species come 

 into being independently of the others? 



We cannot help wondering, for example, how life came into being or 

 how it came to be what it is. More practical questions concern the sources 

 of human qualities, the possible relation between an individual's character- 

 istics and the characteristics and conduct of his parents. How can we preserve 

 useful plants and animals against deterioration? How can we improve the 

 qualities of domestic plants and animals? 



Where did mankind come from? In what way is man related to the rest 

 of life? What is man's destiny? How can we get dependable answers to 

 these questions? What practical difference would the answers to such ques- 

 tions make? 



436 



