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Heritability is a statistic that describes the percent of variance (i.e. variation) in a given trait, in a given population, in a given place and time, that is accounted for by genetic variation within that population. It was originally supposed to be used in studies of plant and animal breeding in agriculture, so it is much more useful in such settings than when used to describe human traits. This is because agricultural organisms and their environments can be carefully controlled and manipulated, whereas human genetic breeding experiments and control of environmental factors are impossible (for both ethical and logistical reasons).[1][2] Therefore, any estimate of the "heritability" of any human trait (e.g. IQ) needs to be taken with more than a few grains of salt because of this problem alone. But the term becomes more meaningless still when one considers that, whether the organism under study is human or not, "heritability" says nothing about genetic determination of a trait at the individual level,[3] nor does it apply to any other population in any other environment.[4]

For example, 70 years ago, most people who would have worn ear-rings would have been women, and most people who didn't would have been men. Hence the variation in who wore ear-rings is very largely explained by the variation in who was a woman or not. This means "wearing ear-rings" would be a highly heritable trait with respect to being a woman. Yet it's blatantly obvious that there's no direct genetic cause for wearing ear-rings, and in fact, it's caused by societal pressures.

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  1. Evolution in Four Dimensions, Eva Jablonka & Marion J. Lamb, 2005, A Bradford Book, p. 357
  2. Heritability: uses and abuses, Genetica, Oscar Kempthorne, 1997, 99(2-3), pp. 109-112
  3. How Heritability Misleads About Race, Ned Block, The Boston Review, January 6, 1996
  4. What is Heritability?, Genetics Home Reference, NIH