From: tai-sa@ailab.ncsu.edu (Scott A Tai)
Subject: T=Intelligence vs Heredity
Reply-To: tai@m-net.ann-arbor.mi.us
Organization: NCSU Artificial Intelligence Systems Laboratory
Date: Tue, 28 Jul 1992 22:34:58 GMT


wchenaul@cyclone.mitre.org (William W. Chenault) writes:

|> I have been told (by a sociology professor, who has studied these sorts of
|> statistics for 40+ years before just recently retiring) that IQ, or the
|> "ability to do well on IQ tests" is half genetic and half environmental.


From Arthur R. Jensen's _The Heritability of Intelligence_:

The Relative Effects of Heredity and Environment
------------------------------------------------

	How can we summarize briefly what is now known about the
relative importance of heredity and environment in causing individual
differences in I.Q.?  In the terminology of genetics a summary answer
consists of saying that the "heritability" of I.Q. is close to 0.80.
This means that 80 percent of the "variance" in I.Q.'s in the general
population is attributable to genetic differences and 20 percent is
attributable to non-genetic or environmental differences.
	"Variance" is essentially a quantitative index of the total
amount of differences that exist among all members of some population.
So instead of talking about variance, we can more easily describe our
conclusions in terms of average differences.
	If we should determine the differences in I.Q. between every
person in the population and every other person, the average of all
these differences would turn out to be 18 I.Q. points.  These
differences are due both to genetic and environmental factors.  Now we
can ask theoretically:  What would be the average I.Q. difference among
all persons in the population if everyone had grown up in identical
environments from the moment of conception, while genetic differences
remained as they are?  Under this hypothetical condition of completely
equal environments for everyone, the average I.Q. difference would be
16 points.  Thus, there would be a reduction of 2 points in the average
difference that now exists.  Let us now ask the reverse:  What would be
the average difference if everyone had exactly the same genetic
endowment, but environmental differences remained unchanged?  Under
this hypothetical condition of complete genetic equality the average
I.Q. difference among persons would be only 8 points, or just half the
difference that would exist with equal environments.
	So the conclusion we come to--which is certainly valid at least
in the white European and North American populations in which the
research was conducted-- is this:  In accounting for the causes of the
differences among persons in I.Q., the genes outweigh the effects of
environment by 2 to 1.  As environmental conditions are improved and
made more alike for all persons in the society, the average
intelligence level of the population will be somewhat increased, and
the I.Q. differences among persons will be slightly reducted.  But of
course the differences that remain will inevitably be due even more to
genetic factors.


-- Scott Tai
   tai@m-net.ann-arbor.mi.us
   "MY KID BEAT UP YOUR HONOR STUDENT."
    -- bumper sticker responding to the tacky honor
       student bumper stickers
   
Newsgroups: rec.org.mensa