BIOLOGY IN HUMAN AFFAIRS 



ration of the central nervous system, resulting in imbecility 

 or feeble-mindedness; absence of iodine in the diet may 

 affect the growth of the thyroid gland, resulting in a 

 condition resembling cretinism. These inductions are 

 supported by thousands of experiments in which the genetic 

 constitution has been held constant, while the environment 

 has been varied; they are supported by thousands of other 

 experiments in which the genetic constitution has been 

 varied, while the environment has been held constant. 



It is not wholly fair to attribute these profound con- 

 clusions to the geneticist, however; the farmer discovered 

 the facts years ago, while the geneticist was floundering 

 in a sea of philosophic doubts. Do not, I beg of you, ask a 

 farmer whether he can turn a hackney colt into a thorough- 

 bred by giving it special food and training, if you wish to 

 retain a reputation for intelligence. Do not ask him what 

 changes can be made in a Concord grape or a Winesap apple 

 or an Elberta peach by an altered soil or a diverse climate. 

 He knows well enough that every plant of each of these 

 asexually propagated varieties has the same genetic con- 

 stitution as all the others, and that, for this reason, they 

 are recognizable members of their respective groups wher- 

 ever they are grown. 



The facts being what they are, therefore, one should not 

 ask whether heredity or environment is the more powerful. 

 It is a silly question. Both are essential. They are collabo- 

 rating artists, their finished product the individual, yet 

 with different roles to play as moulders of destiny. The 

 gene pattern received by the fertilized egg definitely de- 

 limits the end result. One does not gather figs from thistles. 

 Nevertheless, environments can differ to some extent with- 

 out preventing development; and these diverse factors may 

 have a recognizable effect upon the final product. Ordi- 

 narily such effects are restricted to such quantitative 

 changes as we are familiar with under conditions of good 



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