For years commenter Mug of Pee has been saying that HBDers naively assume the Phenotype = Genotype + Environment model.

A good example of this model is sex and height. For example in 1914, the average Canadian man was 5’7″ and the average Canadian woman was 5’2″. Then after 100 years of modern nutrition and health, the average Canadian man is 5’10” and the average Canadian woman is 5’4″.

So even though environment added a few inches of height to both sexes, it did not change the male > female rank order and if expressed in SD units, may not have even changed the gap. The P = G + E model sees environment as a rising tide that lifts all boats but doesn’t change their relative heights. No matter what the environment, having a Y chromosome predicts greater height, while no matter what the genome, 20th century nutrition predicts greater height. In other words, both the genetic effect and the environmental effect are independent of one another and thus can be added together.

By contrast the reaction norm model sees environmental effects as lifting only some boats, while at the same time sinking others. So rather than adding environmental effects to genetic effects, you either add or subtract depending on which environmental effect combines with genomic effect.

While I thought this model was interesting, I couldn’t think of many real world examples.

Then one night I was watching the The evolution of us, a two part documentary on both netflix and amazon prime, which features such luminaries as John Hawkings, Steve Hsu, and Daniel Lieberman. The documentary briefly discussed the Tarahumara.

In their native Copper Canyon environment, the Tarahumara are extremely fit and slim and can outrun white athletes who come and visit, yet when they move to urban areas, they appear to be several standard deviations fatter than white people..

It’s not surprising that the Tarahumara are fatter in an urban environment than in a pre-industrial one (that’s true of all populations). But the fact that they are so disproportionately penalized by an urban environment might be an example of reaction norms.

Of course I know of no evidence of the cognitive equivalent of the Tarahumara: a group that scores as high or higher than whites in one environment, yet scores lower in another.

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