228 



The Journal of Heredity 



sides — the biological and the statistical. 

 An understanding of the facts of biology 

 leads us to expect that heredity should 

 be nearh- all-powerful and the force of 

 environment slight. Ex]jcriments con- 

 firm this expectation. The University 

 of Missouri, for example, is now carrying 

 on a long breeding experiment to deter- 

 mine whether the milking capacity of 

 cows is due to heredity, or whether it 

 is largely dc]:)endent on the good care 

 and feed" they receive. Cows are being 

 subjected to all sorts of treatment at 

 all ages, and the experiment has shown 

 beyond question that the milk-yield is 

 a matter of heredity, and is very little 

 influenced by differences in the treat- 

 ment of cows at any age. In plants and 

 low animal organisms the influence of 

 the environment is considerable, but 

 it diminishes as we rise higher in the 

 evolutionary scale. The student of 

 modern biology can hardly conceive 

 of the possibility that heredity in man 

 should not be more important than 

 environment. 



But that would not be a convincing 

 way of presenting the problem to this 

 audience, and I shall therefore present 

 it largely from the statistical side. 

 When we deal with things that we can 

 measure and express in numbers, we 

 have facts whose value you can decide 

 for yourselves. I shall not try to pre- 

 sent a solution of the problem in general 

 terms, for I do not think it can be done, 

 but I shall pick out a number of definite 

 examples and try to show you the 

 relative weight of heredity and environ- 

 ment in them. 



At the Race Betterment Conference, 

 of which I spoke at the beginning of 

 this paper, Byron W. Holt, a prominent 

 New York social worker, declared, "It 

 will hardly be denied that the two most 

 im]j(jrtant and fundamental causes of 

 prevental;le disease, as well as of crime 

 and race deterioration, are (1) ignorance 

 and (2) poverty." It certainly will 

 be denied; I venture to say that it will 

 be denied, and vehemently denied, ])>• 

 anyone who knows anything about the 

 facts. Such a confusion of cause and 

 effect is the most widespread and 

 serious hindrance to the si)read of 

 eugenic ideas. Because a good environ- 



ment makes it possible for hereditary 

 traits to get ex]3ression, people jum]) 

 to the conclusion that the environment 

 created these traits. The imj^rovement 

 of the environment, aljsolutely es.sential 

 as it is, must ne\'er be neglected for a 

 minute; but our mistake has been in 

 looking on it as an end rather than as 

 a means. It is not an end ; it is merely a 

 means of giving good heredity a chance 

 for expression. If the good heredity 

 is not there, it is hardly worth while to 

 improve the environment: certainly it 

 is a waste of time if it is done with the 

 idea of thereby im])roving a stream of 

 bad heredity in it. 



SOME FAMILIAR EXAMPLES 



The limited effect of nurture in chang- 

 ing nature is in some fields a matter of 

 common observation, if \'ou only stop 

 to think of it in that light. You men 

 who work in the gymnasium know that 

 exercise increases the strength of a given 

 group of muscles, but that this does not 

 go on increasing indefinitely. There 

 comes a time when the limit of your 

 hereditary ]:)otentiality is reached, and 

 no amount of exercise will gain another 

 millimeter in the circumference of your 

 ann. Similarly the handball or tennis 

 player some day reaches his highest 

 ])oint, and e\-en if he redoubles his 

 amount of practice and study of the 

 game after that, he is unable to increase 

 the precision of his shots or the speed 

 of his ];la\-. The same thing applies to 

 runners or race horses — one can do no 

 more than give their inborn ability a 

 chance to express itself. A trainer 

 could bring Arthur Duff\' in a few \-ears 

 to the point of running a hundred yards 

 in QVo seconds, but no amount of 

 training after that could cHp off another 

 fifth of a second; while if the same 

 trainer had had me, t'xcn from child- 

 hood, it is doubtful whether he would 

 ever have gotten me to run it in 10 

 seconds. A ])arallel ca.se is found 

 in the students who take a eoUege 

 examination. Half a dozen of them 

 ma\- have devoted the same amount of 

 time to it — may have crammed to the 

 Hmit — but they will still receive widely 

 different marks. These commonplace 

 eases show that nurture has seemingly 



