10 



RELATION OF CHARACTERISTICS 

 TO ENVIRONMENT 



Its Interaction with Heredity 



We have seen in earlier chapters that all characteristics 

 of organisms, of whatever kind, depend on genes and can 

 be altered by altering genes. This is no more than to say 

 that all properties of organisms, as of inorganic bodies, 

 depend on the materials of which they are made, and can 

 be altered by altering those materials. Changing the genes 

 alters the materials of which organisms are made, and thus 

 may alter any of their characteristics. 



But this leaves open the possibility that other things also 

 may alter any or all of the characteristics. The fact that 

 alteration of genes changes characteristics does not pre- 

 clude their alteration by the conditions to which the or- 

 ganism is subjected during its life and development. In the 

 present chapter we examine the action of environmental 

 conditions on characteristics and their interaction with the 

 genetic constitution. 



To form a correct conception of the interaction of en- 

 vironment and genetic constitution, one must look at the 

 method of manufacture of an organism: that is, at the na- 

 ture of the process of development from an egg to an adult. 

 To certain features of this we now turn. 



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