🚀 go-pugleaf

	I'd like to point out the difference between heritable and
genetic (or inheritable).

	The number of digits a person has is determined by genetic
factors, but that number has a very low heritability.
	Skin color in the United States is very heritable.  In Sweden
and Japan, it has a very low heritability.

	What gives?

	Heritability is not a measure of genetics.  It is a measure of
variation.  It is roughly defined as:

 	h = Genetic variation / total phenotypic variation

where total variation is 
	(genetic variation + environmental variation + error of measure)

	Ergo, the number of digits, a highly genetically determined
trait, but with the majority of variation due to loss of digits by
accident, shows low heritability.
	Since skin color variation in the US (mixture of African
descent and on the opposite extreme Scandanavian descent, and
everyone in between) is extremely genetically determined, heritability
is high.  Whereas in Japan, where the gene pool is much more
limited, skin color is more determined by whether one lives in the
city or works as a farmer.  The observed phenotypic variability is
due almost solely to number of hours spent in the sun, hence
heritability very low.

	IQ scores are heritable trait.  No less so than height or weight. 
It is not perfectly heritable, and in fact, it's heritability varies
among population groups: it is higher in whites than in blacks in the
US, presumably because there is more environmental variation between 
black communites.
	Furthermore, as first pointed out by Jensen, attempts to
improve the environment will, paradoxically to some, make IQ scores
MORE heritable, since they will eliminate environmental variation
from the denominator without touching the numerator.
	While many would argue this point, that means in an ideal
system, the best possible environment for every person, that IQ
would be 100% heritable. 

	Stephen J. Gould makes a very good case against those who
equate heritability with genetic determinism.  Unfortunately, he
makes the same mistake in most of his rebuttal arguments.
	So, I ask you, before comitting yourself to the argument,
think several times about this definition of heritability.  It is
definitely a non-trivial point.

	Maybe I should dig out my old IQ series, update it, and
repost it.  Maybe not?  Feedback is requested.
-- 
			      Craig Werner (MD/PhD '91)
				!philabs!aecom!werner
              (1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517)
               "Why is it that half the calories is twice the price?"