SIGNIFICANT EVIDENCE 



FOR MENTAL HEREDITY 



Much Supposed Proof Worthless Problem Is One of Human Differences, and 

 Must be Approached Objectively Evidence from Twins, Royal 

 Families, and Eminent Men -Difficulties to be Avoided' 



Frederick Adams Woods 

 Lecturer on f->iolo(iy. Massachusetts Institute of Technology. Boston 



AW discussion of the significanl 

 c\-idence for mental heredity 

 L must aim at unravelling the 

 part taken by heredity as opposed 

 to external forces of nature commonly 

 called the environment, and also as 

 opposed to a possible internal force, 

 acting apart from the known laws of 

 nature and commonly called free-will. 

 This latter aspect i^ usually ignored in 

 scientific discussions of the question; 

 but it should not be ignored. As a 

 matter of fact, for countless ages 

 millions of people have been, and are 

 today, firm believers in the existence of 

 spiritual forces capable of overcoming 

 the material world and directing molec- 

 ular change. It is easy to see that if 

 the doctrine of reincarnation is stricth' 

 true, so that souls pass from one 

 body to another at haphazard, and if 

 it makes no difference whose infantile 

 body one happens to vitalize, then there 

 can be no mental and moral resemblance 

 between father and son, brother and 

 brother, .=ister and sister, or decreasing 

 family resemblances as the relationshij) 

 becomes more remote. The i:)hysical 

 resemblances would be there, but the 

 supposed spiritual resemblances would 

 be a sham. There is no scientific reason 

 a priori why this should not be so. 

 It would be just like us to deceive 

 our.selves on a jjoint like this. The 

 transccndentalist, transmigrationist, 

 idealist of whatever school, might 

 well say, "You scientists see the facial 

 resemblance and you imagine the rest. 

 You pick out instances of mental 



^:imilarit}' between father and son or 

 between other relatives, but these are 

 the exceptions. Of course, out of all 

 the people of the community you can 

 find some instances of spiritual resem- 

 blances. Living in the same mental 

 and moral atmosi)here would account 

 for that." The idealists might say, 

 "We ourseh^es believe in education and 

 the value of a good example. The 

 researches of the scientists amount to 

 nothing — they prove nothing more than 

 a general tendency of similar traits to 

 be found in similar home and social 

 life." 



I regret to say that a very large 

 portion of the published literature 

 on mental heredity is open to this 

 criticism and proves nothing at all as to 

 the relative importance of heredity. 

 Many text-books, magazine articles, 

 readable books on eugenics, books on 

 biology containing chapters on human 

 heredity, are worse than the primary 

 literature itself. Why this should be 

 so I do not know, but I sui)pose that 

 in the desire of the writer to make the 

 book or article, first of all interesting 

 on the human side, he takes any kind 

 of evidence that happens to make a 

 human appeal. It is essentially a 

 human question, and that means that 

 it is very ditlicult to get a disinterested 

 discussion. This is not true of most 

 departments of natural science. In 

 chemistry, phy.sics, geology, astronomy, 

 it makes very little diflerencc to human 

 l^ride how the theories work out, but 

 in the question of human hereditv 



* Read in New York City before the thirteenlli annual meeting of the American Genetic 

 Association, December 27, 1916. 



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