The Fallacy of Estimating "Heritability" in Medicine and the Behavioral Sciences
By Jay Joseph. Psy.D
(Adapted from a 3/13/2021 twitter post https://twitter.com/jayjoseph22/status/1370785425955065860)
1/ Critics argue that “heritability” is a misunderstood and misused concept, and that “heritability estimates,” which range from 0% to 100% (0.0 to 1.0), do not tell us “how much” genes contribute to human behavioral differences, or how “fixed” human behavior is.
2/ Using the example of the disease favism (Glucose-6-phosphate
dehydrogenase deficiency), I illustrate the fallacy of using
heritability estimates to assess “how much” genes influence behavior (“IQ,”
“personality,” psychiatric conditions, and so on).
3/ Favism is caused by an inherited deficiency of
glucose-6-phosphate. The predisposing gene is located on the X chromosome. When
the carrier eats fava (broad) beans or inhales fava bean pollen, favism
appears. The disease is marked by the development of hemolytic anemia.
4/ In other words, “beans and genes” are both necessary
for favism to appear. In the human behavior area, critics often dispute claims
that "genes for behavior" have been discovered.
5/ Let’s imagine “Country A,” where all citizens
(100%) carry the favism gene. In Country A, 15% of the citizens, all of
whom of course carry the gene, are exposed to fava beans and subsequently develop
favism.
6/ In Country A, because all citizens carry the gene,
but only some were exposed to fava beans, all favism variation is
caused by environmental factors (fava bean exposure or non-exposure). The “heritability
of favism” in Country A, therefore, is 0% (0.0).
7/ At the same time, it would be very mistaken to
conclude that genes play no role in developing favism in Country A, or that the
genetic influence is weak or irrelevant. A genetic
predisposition is, in fact, a prerequisite for developing favism.
8/ Now imagine “Country B,” where all citizens
(100%) eat a diet containing fava beans. In Country B, 15% of the citizens, all
of whom of course eat a diet containing fava beans, carry the favism gene and
subsequently develop favism.
9/ In “Country B,” because all citizens are exposed
to fava beans but only some carry the gene, all favism variation is
caused by genetic factors (carrying or not carrying the gene). The “heritability
of favism” in Country B, therefore, is 100% (1.0).
11/ In the above examples, the “heritability of
favism” simultaneously is 0% in Country A, and 100% in Country B, even though
the causes of favism are the same in both countries.
12/ As we see, “heritability estimates” assess
variation as opposed to cause, and do not at all indicate the strength or
weakness of the genetic influence—or by implication the strength or weakness of
the environmental influence.
13/ The use of heritability estimates as an indication of "how much" genes influence behavioral characteristics (traits) or diseases should end. Heritability was developed as a breeding statistic in agriculture, and this remains its only valid use.
Further reading:
Chaufan, C., (2008), Unpacking the Heritability of Diabetes: The Problem of Attempting to Quantify the Relative Contributions of Nature and Nurture, DataCrítica: International Journal of Critical Statistics, 2, 23-38.
Hirsch, J., (1997), Some History of Heredity-vs-Environment, Genetic Inferiority at Harvard (?), and The (Incredible) Bell Curve, Genetica, 99, 207-224;
Joseph, J., (2004), The Gene Illusion: Genetic Research in Psychiatry and Psychology Under the Microscope, New York: Algora (Chapter 5).
Joseph, J., (2015, June 24), Are DSM Psychiatric Disorders “Heritable”?, [Web log post, Mad in America “The Gene Illusion in Psychiatry and Psychology”].
Keller, E. F., (2010), The
Mirage of a Space Between Nature and Nurture, Durham, NC: Duke University
Press.
Moore, D. S., & Shenk, D., 2016, The Heritability Fallacy, WIREs Cognitive Science, doi: 10.1002/wcs.1400
Stoltenberg, S. F., (1997), Coming to Terms with Heritability,
Genetica, 99, 89-96.
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