OUR FUTURE COURSE 203 



environment include both substances and stimuli. 

 A true appreciation of these facts demands the 

 complete discard of the older views. We must 

 forget that we have had three-quarters of a century 

 of bickering over the environment and the heritage 

 as alternative causes of evolution and begin anew 

 with a recognition of their essential and coordinated 

 functions, for in no single case have we observed a 

 significant organic change which could be ascribed 

 to either alone. 



The modification of the heritage, while it may 

 be brought about through the action of penetrat- 

 ing irresistible forces of chemical or physical nature 

 on the germinal chromosomes, as by alcohol or 

 X-rays, may also be sought in the variable environ- 

 mental conditions which give it the opportunity 

 for variable expression of its inherent properties. 

 It is generally recognized that the inherent powers 

 of the specialized tissues which make up the body 

 are governed by the genes which associate these 

 tissues with the preceding generation. If the indi- 

 vidual receives one type of genes it may deposit 

 pigment normally, if another it may freckle, and 

 if a third it may be an albino, but whichever may 

 be its heritage, it was represented in the chromo- 

 somes of the germ cells with which development 

 started. 



Some of the inherent powers of the chromosomes 

 are realized, as development proceeds, in spite of 



