274 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
4. The tetrakinetic theory of H. F. Osborn: This is a recent restate- 
ment in energistic terms, of the causo-mechanical basis of evolution. 
It is placed in the next chapter, but cannot fully be understood until 
the subject of genetics has been presented. 
It is almost impossible satisfactorily to pursue a further study of 
the causal factors of evolution without encroaching upon the field that 
is now called genetics, and so we shall pass without further explana- 
tions to a consideration of this field of experimental and analytical 
evolution. 
