Darwin-L Message Log 1:200 (September 1993)

Academic Discussion on the History and Theory of the Historical Sciences



<1:200>From mayerg@cs.uwp.edu  Fri Sep 24 08:17:53 1993

Date: Fri, 24 Sep 1993 07:59:44 -0500 (CDT)
From: Gregory Mayer <mayerg@cs.uwp.edu>
Subject: Re: Heritability and cultural evolution
To: darwin-l@ukanaix.cc.ukans.edu

	In his posting of 23 September, Elihu Gerson cautions us against
using the one term heritability for both biological and cultural
transmission, for while they are similar, calling them the same thing
might obscure important differences.

	I would like to endorse his call for careful use of language and
terminology in discussing these phenomena.  While heritability could be
expanded in meaning to include cultural transmission, it might well be
best to restrict it to its well defined biological meaning.  It is not
quite right to define heritability (in the quantitative genetics sense),
as Richard Burian has, as the correlation of parents and offspring.  It is
indeed true that parent/offspring correlation is a common experimental
design for estimating heritability, but it is not the definition of
heritability, nor the best experimental design.  Heritability is defined
as the proportion of the total variance among individuals (= the
phenotypic variance) that is due to genetic variance among individuals.
The phenotypic variance also has an environmental component, and the
genetic variance can be further decomposed into additive, dominance and
interaction components.  More complex analyses of the variance to include
further complications such as, e.g. genotype/environment correlation, are
possible.  The key point is that heritability is not just a correlation
among parents and offspring (which can be similar for all sorts of
reasons), but, by definition, a genetic (in the biological sense)
phenomenon.  Quantitative geneticists design their experiments so as to be
able to estimate the various components, genetic and non-genetic, of the
phenotypic variance.  Thus if we were interested in the heritability of
dialect, the first experiment a quantitative geneticist would think of
would be to raise offspring from one dialect group in a different dialect
group.  Experiments much like this have been done to study song dialects
of birds.  If we did such an experiment with humans, we would find the
heritability to be zero: an American child, raised from birth by a
Brazilian family in Brazil, would speak Portuguese.  The same, I would
wager, would be true of dialects.  There is, of course, an interesting
cultural transmission of language in our American/Brazilian gedanken
experiment, but it does not involve a non-zero quantitative genetic

The second point worth mentioning about this is that heritabilty
is an analysis of _variance_, i.e. of differences among individuals, and
says nothing about mean values.  If we did Richard Burian's study of
heritability within a stable dialect, we would again find zero
heritability.  This time it would not be zero contingently, as in the case
of the American child in Brazil (it _could_ have been the case that
language was inherited genetically in man, as it is, in part, in some
birds; it just happens that it isn't).  It would in this case be zero by
definition, because there would be no differences among individuals,
since, by the setup of the example, they all spoke the same dialect.
Again, there would be an interesting cultural transmission of language,
but the quantitative genetic concept of heritability would not be a useful
analytic tool.  Heritability is a way of relating differences among
individuals to differences in their genes, environment etc.

Those interested in the details of heritability in the
quantitative genetic sense should look at D.S. Falconer, 1989,
_Introduction to Quantitative Genetics_, Longman, Harlow, Essex, and for
an account of the limitations of this approach at R.C. Lewontin, 1974, The
analysis of variance and the analysis of causes, _Amer. J. Hum. Gen._

Gregory C. Mayer

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