Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!ptsfa!ames!ucbcad!ucbvax!jade!tart7.berkeley.edu!c60a-4er
From: c60a-4er@tart7.berkeley.edu.UUCP
Newsgroups: sci.bio,sci.misc
Subject: Re: Knowledge and the Academics
Message-ID: <3957@jade.BERKELEY.EDU>
Date: Mon, 15-Jun-87 00:58:21 EDT
Article-I.D.: jade.3957
Posted: Mon Jun 15 00:58:21 1987
Date-Received: Tue, 16-Jun-87 01:43:03 EDT
References: <16224@brahms.Berkeley.EDU> <160200002@inmet> <2172@mmintl.UUCP> <123@snark.UUCP> <16745@cca.CCA.COM>
Sender: usenet@jade.BERKELEY.EDU
Reply-To: c60a-4er@tart7.berkeley.edu.BERKELEY.EDU
Organization: University of California, Berkeley
Lines: 27
Xref: utgpu sci.bio:379 sci.misc:284

A trap to beware of in any discussion of the heritability of IQ:

The definition of "heritability" commonly used by population geneticists
and such is not quite the same as the common meaning of the word.  The
definition is this: heritability is the amount of the variation within
the population under consideration (with regard to a particular trait)
that can be attributed to heredity.  The words "within the population
under consideration" are tremendously important.  Within inbred mouse
strains, for example, size of body has a very low heritability--since the mice
are practically identical genetically, almost all the variation is due to 
birth order, feeding, etc.  However, in wild mice size is quite heritable.
     The point is, that figure of 80% heritability of IQ means that within
the population under consideration, about 80% of the observed variation
appears to be genetic.  It DOES NOT mean that, for example, no possible
environment will make more than a 20% difference in IQ--an obviously false
statement (consider massive brain damage as an environmental condition).
     I realize that this sounds like a semantic quibble, but it's not.
It is very easy to draw nasty false conclusions from heritability statistics.
An example:  mental retardation due to phenylketonuria was, until the
disease was understood, nearly 100% heritable--much more heritable than IQ.
However, appropriate treatment early in life will prevent such retardation.
Can we be sure that there is not some equivalent of "appropriate treatment"
(I don't mean drugs or surgery, I mean maybe better education and home environ-
ment) to benefit those with "heritably" lower IQ?

Mary K. Kuhner
"the dance of the nucleotides, the fourfold sarabande..."