268 ESSENTIALS OF BIOLOGY 



they occur ; this, of course, is the real problem. (3) Finally, 

 we have the almost obvious hypothesis of bodily changes occurring 

 as the expressions of needs and desires, and then the gradual 

 modification of the developmental organization by these bodily, 

 individually acquired changes. We easily see, from the literature, 

 that experimental evidence in favour of such a hypothesis exists 

 but is, at the best, inconclusive and not generally accepted. But 

 even if such evidence were beyond question we have still to extend 

 it to wild nature and show that something happens there compar- 

 able with what our experiments do. So we are again in the phase 

 of biology that preceded the work of Darwin. Experiment 

 suggests conclusions that can only be applied to the study of the 

 evolutionary process after far more work of the purely natural 

 history kind than is now being attempted. It is the study of 

 wild nature, without experiment, that must be the next big step 

 forward. 



