34 THE PROBLEMS OF EVOLUTION 



tinuous process of change inherent in living things 

 and species as merely stations along its course.® 

 The point of view is easily harmonized with all 

 sound ideas of evolution and need not affect our 

 approach. Species are the units of evolution, and 

 as such must be the chief concern of the evolution- 

 ist, but in the very nature of their existence he 

 must appreciate their impermanence. He must 

 work also with individuals and must appreciate 

 to the full their significance in his problem. 



Here is a vital point in his progress. He must not 

 fall into the sociological error of opposing individ- 

 uals to species in estimating values. He must not 

 fall into the biological error of regarding the phe- 

 nomena of individual existence as independent of 

 the characteristics of species. And he must not 

 fall into the philosophical error of satisfying him- 

 self with concepts whose reality cannot be demon- 

 strated within the bounds of science. If he succeeds 

 in observing this trio of don'ts we may expect his 

 results to be sound, even though they may be 

 meager in the present state of our knowledge. 



The nature of living beings has been briefly 

 stated in the preceding chapter. We are unable to 

 say that life is produced from non-living materials 

 at the present time, or even to predict with reason- 

 able certainty the possibility or impossibility of 

 such additions to the living world. The old princi- 



« Cook, O. F., Ann. RepL Smiths, Inst, 1904, pp. 397-412, 1905. 



