It’s Not (All) About Genes

August 2, 2013 By arne hendriks 0

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There is a strong correspondance between the heights of offspring and the average height of the two parents. In Western societies this amounts to height being up to 90% heritable. But although who your parents are is the predominant determination of height, it’s no excuse for it.

Heritability statistics do not reflect the relative importance of genes in explaining height. They reflect what causes the variation but say nothing about what causes height itself. In fact genetic heritage isn’t necessarily more important than environmental factors in causing people’s heights. Evolutionary biologist, and prominent adversary of genetic determinism,  Richard Lewontin devised a simple and insightful demonstration to show this. He planted ordinary, genetically diverse seeds into two radically different environments and allowed them to grow to their full heights. One environment had barely enough light, nutrients, and water for survival and stayed small. The other environment was enriched with ideal amounts of light, water, and nutrients and grew tall. All of the variation in height within each tray was due to the genetic diversity of the seeds, since the seeds developed in identical environments, and therefore the variation observed in the heights of the plants within a tray cannot be attributed to differing environmental factors. So regardless of the environments in which the plants grew, heritability is 100 percent within each tray. Yet obviously environmental factors played a large role in each individual tray, so even if heritability is 100 percent, the environment has very powerful effects on the appearance of a trait. It’s in your genes but it’s not. We determine how to express them.