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39  Nature versus Nurture
    The Washington Post, Sunday, April 9, 1967

     Which is more important for human development, heredity or
environment?  This question about "nature versus nurture" is the one
most often asked of the human geneticist.  It is far too crudely
stated to be of much value in unifying the scientific understanding
of man, but we must find some way of dealing with it -- if only
because it is so often asked.

     Before we can attempt to appraise the scientific evidence, we
have to clarify the question.  Then we can consider ways to answer
it.  Both steps involve treacherous confusion.

     By taking extreme examples, it is easy to prove either side of
the issue.  Men are almost always more resourceful than monkeys.  The
essential difference between man and monkey is heredity -- the
chemistry of DNA molecules.  Monkeys reared in the most stimulating
environment never approach human intelligence.

     But it must be pointed out that much of the difference -- the 
culture that includes language, agriculture, social organization,
industrial skills -- comes from the environment that man has created.
It is possible that only a small enlargement of the monkey's brain,
to facilitate its speech, is all that stands between it and the
emergence of new cultures analogous to the human.

     In other circumstances, environment may be the overriding factor.
A fetus of impeccable genetic quality may be so impaired by a prenatal
attack by German measles virus that it cannot survive, or if it does
and continues its distorted development, it may have lost too many
brain cells to have any hope of expressing the promise of its DNA.

     Man versus monkey, or brain-damaged versus healthy, are extreme
examples of hereditary and environmental differentials, but the same
principles apply to the infinite gradation of subtler differences in
human heredity and experience.

     The nature-nurture issue has no universal answer; it must be
looked at existentially.  If we see differences in performance within
a group of people, or between groups, we can ask a specific question
about that group.  Of the total observed variability in IQ, income
or education in a group, what fraction can we attribute to variations
in heredity and what fraction to variations in environment?

     If we also take into account the interactions between the two
terms, the fractions must total 100 percent.  Thus, we could 
standardize the environment of a given group and then all of its
variability would have to be genetic.  If we standardized the genetics
-- for example, by dealing with identical twins -- the observed 
variability would have to be environmental.

     If environment and hereditary are both variable, as is almost
always the case in human affairs, we also have to consider whether
the two are optimally matched.

     The nature-nurture issue has been raised in the most pointed
fashion in connection with race.  The performance of Negroes in
academic and economic competition in the United States is an urgent
social problem.  Sensibleness  tells us we must concentrate on
individual performance, not group labels.

     Nevertheless, it has been asserted that we ought to narrow our
expectation for the ultimate catchup of minority races because they
might have some hereditary limitation.

     We are not very knowledgeable about how to identify the most
crucial factors in nurturing the intellectual and social development
of a child.  However, one would have to be studiously blind not to see
an ample explanation of racial lag in the existing discriminatory
environment.

     But, the retort goes, it is well known that a large part of the
differences in intelligence are hereditary; therefore the minority
groups must, to the same extent, be genetically inferior.  This is
the fraud of translating measurements in one homogeneous group to
predictions about inter-racial differences.

     Until the environments are made comparable, or until the whole
process of the development of intellect is scientifically
well-understood, we have no way to draw any conclusions whatever about
the nature of racial difference.

     Fortunately, we are committed by law, and by our confrontation
with conscience and reality, to make the experiment; to find out how
far human performance can be liberated by removing the burden of
discrimination.

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