“Genomic Findings and Their Implications for the Evolutionary Social Sciences”, 2024-07 (; similar):
What past selection pressures have shaped human traits and their variation and covariation across individuals? These are key questions in the evolutionary social sciences. Recent advances in the field of human genomics have yielded a wealth of evidence that sheds light on these questions, yet the findings and their implications seem to be little known in the evolutionary social sciences.
In this paper I aim to bring together these findings while explaining the conceptual and technical background that is often assumed knowledge for reading the primary reports. First, I outline the genomics methodologies that have enabled the relevant findings, such as genome-wide association studies and DNA-based heritability estimation. I describe how these methodologies reveal the genetic architecture of traits, and then how this information in turn enables inferences about past selection.
The findings show pervasive evidence that the genetic architecture of complex traits has been shaped by negative (purifying) selection, implying that the extant genetic variation in the traits has been maintained by mutation-selection-drift balance. On the other hand, there is no evidence that balancing selection has substantively shaped complex traits, and strong evidence that it has not.
Finally, I discuss the implications of these findings for issues such as the dimensional structure of personality variation and the plausibility of psychological life history theory.
[Keywords: mutation-selection balance, evolutionary psychology, behavioral genetics, negative selection, balancing selection]
…What do these findings mean for the evolutionary social sciences? Most obviously, they mean we should not reach for balancing selection as an evolutionary explanation of individual differences, at least in the absence of powerful evidence for a specific trait. Understandably, balancing selection has been a common go-to explanation when the question arises of how heritable variation in human traits is maintained. 2010 reviewed a plethora of individual differences proposed to be maintained by balancing selection, including promiscuous and monogamous individuals, cheaters and cooperators, progressives and conservatives, risk takers and hesitators, long-term planners and short-term opportunists, and aggressive hawks and peaceful doves. Indeed, various authors have argued that variation in personality traits in general is maintained by balancing selection (de et al 2016; 2006; et al 2007). Given the pervasive evidence, described above, against balancing selection having shaped the genetic variation in a wide range of complex traits, this possibility seems highly unlikely. Furthermore, most of the evidence above directly features the personality trait neuroticism, which is often included in large GWAS datasets because of its relevance to mental health. Other personality traits have not been subject to GWASs with quite so large samples, but they clearly show genetic architectures consistent with negative selection and not balancing selection (Verweij et al 201212ya). This evidence is often misconstrued. For example, de et al 2016 dismissed et al 2012’s evidence by saying that SNPs only accounted for a small proportion of the genetic variation, and so were uninformative about the overall genetic variation. But as we had made clear, it is the very fact that SNPs only account for a small proportion of the genetic variation that is revealing of the important point about the overall genetic architecture—that is, common genetic variation, the vast majority of which is captured on SNP chips, does not account for the vast majority of the total additive genetic variation in personality traits as would be expected if the variation had been shaped by balancing selection (or even selective neutrality) (Verweij et al 201212ya). In sum, using balancing selection as an explanation for personality variation flies in the face of the available evidence.
…Here too, the evidence and its implications are often misconstrued. Del 2020, for example, argues that the transience of episodes of balancing selection in human traits probably explains the lack of evidence of its having shaped genetic variation. But it is long-term balancing selection that et al 2019 proposed could align genetic variation in traits along a fast-slow dimension. It does not make sense to claim that balancing selection is too transient to have left any trace in the genetic variation of traits but also claim that it has shaped the covariation among traits. Del 2020 also argues that balancing selection is not expected to produce common variants of large effect. But the expectation is not that balancing selection produces common variants of large effect; rather, naturally occurring variants of large effect would be expected would be among those maintained by balancing selection. As explained earlier (§3.2.1), we know complex traits are influenced by variants with large effect sizes ( et al 2023); the fact that these variants are always rare and never common (see also §3.2.3) is expected under negative selection but not under balancing selection. To the contrary, genetic variants (including those of large effect) maintained by balancing selection would be expected to be common, not rare, as all modeling shows that balancing selection maintains variants at intermediate frequencies if at all.