FUNCTION AND ENVIRONMENT 201 



theory, and believe that the giraffe lengthened 

 its neck by stretching it; yet we must be- 

 ware of taking too simple a view of what 

 function implies. What are the certainties ? 

 We know that development the expression 

 of an inheritance demands functional as 

 well as environmental stimuli. Practice 

 makes an organ possible. Without exercise 

 it will not develop fully. Again, we know 

 that changes in function have great individual 

 importance. By force of smiting one be- 

 comes a smith. Even if there be no multi- 

 plication of muscle-fibres after the more 

 strenuous function began, each fibre is larger 

 and worth more. Contrariwise, disuse means 

 deterioration; when we rest too much we rust. 

 No one has ever doubted the individual im- 

 portance of functional modifications. Further, 

 although the transmission of a functional 

 modification remains unproved, the secondary 

 and indirect results may influence the germ- 

 cells and the offspring. It is idle to say that 

 what living creatures do or fail to do has no 

 racial importance. Another certainty is that 

 by its activity a living creature, being no 

 mere puppet of fate, may alter the whole 

 situation. This, again, may have evolu- 

 tionary interest, even if it ends fatally. 

 Admitting all this, can we say more ? 



