April 30, 1971
Dear Francis:
I have been very busy, and hence slow in responding to your letter of 29th March.  Also I am about to leave for three weeks in Europe, so I will reply briefly.
The Twins' Institute might provide valuable additional data; much has already been learned from the study of twins, and much more can certainly be learned.  I would hesitate to encourage people to give away one of the pair of twins for adoption; if the parents can bring up both twins, it is usually better for the children.  But certainly more systematic efforts to study twins brought up separately would be worthwhile.
As to intelligence, I am quite sure that no one can have high intelligence unless he has a favorable constellation of genes.  There may be a great many such favorable combinations; intelligence is not a single entity.  In any case, a child of potentially high intelligence may be converted into an idiot by a brief cutting off of the oxygen supply to the brain during a difficult birth.  Malnutrition in early childhood may damage intelligence irreversibly; and there are almost certainly social and psychological factors that may, operating in childhood, prevent the individual from rising to anything like his full potential.  Thus the situation is, I think, highly complex.  It is even more complex when one considers the hereditary and environmental factors involved in the development of character traits such as kindness, generosity, and sense of responsibility.  Research in this field is bound to give results slowly, even if you pour a lot of money into it.
There is a matter of priorities here.  I think, for instance, that stopping human population growth is a matter of the highest priority, and enormously difficult.  It deserves a far higher priority, to my mind, than the issues raised by Jensen and Shockley.  I am not against eugenics in principle; within a generation, as knowledge of human heredity advances, we may be in a position to begin an effective program of positive eugenics.  Eugenics has got a bad name because some people tried to push it at a time when there was not adequate scientific basis for doing so; and of course it had the misfortune that the Nazis promoted something to which they gave the name of eugenics. But at present I believe that the problem of human numbers is overriding; the most urgent problem in applied biology is to control that; and of course that also involves social and psychological problems that go far beyond pure or applied biology.
Best wishes.
Yours sincerely,
John T. Edsall