42 EVOLUTION AND GENETICS 



that they are no longer advancing, and that only a 

 few species are producing new or better types. 



While it is well to keep these possibilities in mind, 

 an appeal to the actual evidence furnishes no grounds 

 for the belief that the process of evolution has come 

 to an end. The conditions of land, water, and atmos- 

 jihere have in all probability changed slowly since 

 life first aj^peared, as they are changing today, and 

 if in the past, evolution has progressed while the ex- 

 ternal world has been so slowly changing, it is a fair 

 presumption that, to some extent at least, we may 

 exjDect to find evolution taking place at the present 

 time. It should also not be forgotten that the re- 

 adjustment of animals and plants to each other may 

 be as important a condition of evolution as their 

 adjustments to the external world. From the latter 

 point of view, the extraordinary complexity of the 

 relation of living things to each other may even seem 

 to furnish ample ojiportunities for further adjust- 

 ments. It is certain, at least, that with the advent of 

 man's interference with the natural conditions es- 

 sential to other animals and plants, widespread 

 changes may be expected to take place in part de- 

 structive but possibly also constructive. His domes- 

 tication of several kinds of j)lants has produced 

 changes in them that are very striking, but whether 

 by the same kind of processes that take place in 

 nature is a matter of dispute. 



There is then, on the whole, a fair a priori expec- 



