>The phenotypic level shows a negative correlation between cognitive ability and risk for schizophrenia (Keefe, 2008).

>A similar trend is hypothesized for depression, negatively correlated to complex cognition (Cullen et al., 2015; Lim et al., 2013; Snyder, 2013).

>Autism, especially high-functioning autism or Asperger’s syndrome, is predicted to follow a similar trend as IQ and EA (Grove et al., 2019). Urban societies may have influenced the selection for autism-related traits while presenting challenges for individuals with schizophrenia (Lederbogen et al., 2011; Marcelis et al., 1999; van Os et al., 2010).

>Anorexia has a notably large positive relationship to intelligence, and its historical trend would be interesting.

>However, the data do not support the cold winters theory of intelligence (Lynn, 1991, 2006), as the effect of latitude on EA3 and IQ in the regression models (Supplementary Tables S1 and S3) tended to be slightly negative (β = −0.055 and −0.097, p = .022 and p < .001 respectively), contrary to the theory’s prediction. This implies that, at least within the temperate zone from which our samples were derived (30.64 to 69.65°), and within the last 12,000 years, climate did not exert a discernible selective pressure.

>Indeed, Eastern Hunter Gatherer ancestry, which derived up to 70% of ancestry from Ancient North Eurasians living in the extremely cold climates of Siberia (Posth et al., 2023), was a negative predictor of EA or IQ in the regressions.

>Hunter-gatherer ancestry (particularly V2 or WHG) was negatively associated with EA3, EA4 and IQ in the regression models (Supplementary Tables S1−S3) even after accounting for Years BP (β = -0.314, -0.4, -0.249), suggesting that the increase in cognitive capacity was not solely driven by the Neolithic revolution but was partly mediated by admixture with the immigrants that accompanied it.

>There are some non-continuous changes in some genetic scores. These relate to population replacements. The farmers seem to be smarter than the hunter-gatherers, and their replacement increased intelligence faster than within population would have done. Group selection in action.