Chapter 6 



Changing Plant and Animal Nature 



THE so-called evidences of evolution so far discussed 

 are what the lawyer would consider indirect or cir- 

 cumstantial. Is there any direct evidence of the 

 transformation of species? 



If plant and animal forms have in the past become 

 modified in the course of descent, there is no reason to think 

 that the processes have ceased. The processes which may 

 have resulted in the rise of new plant and animal forms 

 should be observable now. The only qualification which 

 may have to be considered is that of time. The supposed 

 evolution of the forms whose records are fairly complete 

 must have taken thousands and millions of years. Our ob- 

 servation can be applied to a negligible fraction of such a 

 time. The slowness of the process, however, does not re- 

 lieve the biologist of the responsibility for capturing the 

 facts. The astronomers have been able to measure move- 

 ments of the " fixed " stars which to the ordinary observer 

 are indeed fixed in their relative positions from century to 

 century. They have also been able to measure a wobbling 

 of the earth's axis which completes its circuit in 25,000 

 years. The physicists have been able to measure the dis- 

 integration of heavy elements like uranium as fractions 

 of a process extending over millions of years. The geolo- 

 gist, dealing with earth changes that have taken millions 

 of years, can find and measure the processes involved as 

 they go on before our eyes. In the same way, the biologist 

 has been able to catch the process of evolution in the act, 

 so to say. 



