Natural Selection in Modern Humans
Three generations of selection against educational attainment in the U.S.
A new paper in the journal Behavior Genetics looks at natural selection in three generations of modern Americans. The graph below shows the key results. Specifically, it shows the strength of selection for a range of traits based on the sample’s polygenic scores (PGS; see here for details). Among other things, we see selection against educational attainment and cognitive performance, and selection for depressive symptoms, asthma, earlier age of first birth, and lower self-rated health.

Here are some excerpts from the paper.
Looking at the polygenic scores changing the most, many seem to have moved in the opposite direction to how the phenotype has changed over the latter half of the twentieth century. Education, IQ, delayed child birth, abstinence from smoking and life expectancy have all increased in the late twentieth century, contrary to how we believe the genetics have changed. However, the prevalence of self-reported anxiety and depressive symptoms has increased (Witters and Dan 2023; Twenge 2000), paralleling the polygenic scores for depression and neuroticism. The prevalence of asthma has also increased (Moorman et al. 2007) in line with the polygenic score. The apparent paradox of phenotypes and natural selection moving in opposite directions suggests that environmental change is a much stronger force than that of natural selection across recent history…
Patterns of selection appear consistent across the twentieth and early twenty-first century... The underlying causes of selection seem to have stayed the same over time, so that the effects of selection have accumulated. In particular, selection against traits associated with education clearly predates the development of the US welfare state…
Our estimate of how much natural selection is changing intelligence is slightly smaller than in previous work. For example, Kong et al. (2017) provide an estimate of −0.9 IQ points every 30 years in Iceland, compared to our −0.6 points per generation. However, cognitive traits are only one part of the story of natural selection in humans. Whilst past research has focused on these traits, we find selection differentials are often of similar magnitudes for health related traits. The selection differential for self-rated health is greater than those for education and cognitive performance. The most significant, positively selected trait was ADHD, which was also found in the UK (Hugh-Jones and Abdellaoui 2022). Future research should study the health and medical implications of natural selection, in addition to its social implications. To know more, we must await more accurate polygenic scores.
The paper is titled “Natural Selection Across Three Generations of Americans,” and was authored by David Hugh-Jones and Tobias Edwards. You can access it here, or request a free copy from the authors here.
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