The same genes predicting educational attainment also predict a woman's age at first birth, body mass index, and household wealth. This suggests selection acts not on "studiousness" but an underlying trait like executive function or propensity to defer gratification, which manifests differently across environments.

Contrary to expectations of increasing societal complexity, the strongest selection for genetic variants predicting modern IQ test scores and educational attainment occurred between 4,000 and 2,000 years ago. In the last 2,000 years, including the industrial revolution, there has been no detectable selection on these traits.

To test if the "years of schooling" genetic signal was an artifact, researchers applied it to a separate dataset of Chinese individuals. The fact it still predicted educational outcomes strongly suggests the genes are linked to a fundamental, cross-cultural biological trait, not just a quirk of European society.

Genetic data shows natural selection on immune and metabolic traits intensified dramatically 5,000 to 2,000 years ago. This suggests that high-density living and close contact with animals during the Bronze Age created a more powerful evolutionary pressure than the initial shift to farming.

All populations that developed agriculture descend from ancestors who lived long before its invention, implying the necessary cognitive abilities were in place. The simultaneous, independent emergence of farming worldwide points to a global environmental trigger: the unprecedented climate stability of the last 12,000 years (the Holocene).

Most changes in gene frequencies are due to population movements (migration) and random chance (genetic drift), which create statistical noise. The true signal of adaptation is a tiny fraction (2%) of this noise, explaining why it was so difficult to detect with smaller datasets before recent methodological breakthroughs.

The Polygenic Index (PGI) summarizes thousands of minor genetic effects into a single predictive score for complex outcomes like educational attainment or heart disease. This 'age of genomic prediction' will radically alter social domains like insurance, education, and even embryo selection, creating profound ethical challenges.

Counterintuitively, the heritability of traits like cognition and personality increases from childhood into adulthood. This occurs because individuals increasingly select and shape their own environments based on their genetic predispositions, a process that amplifies the influence of their genes over time.

In restrictive environments where choices are limited, genetics play a smaller role in life outcomes. As society provides more opportunity and information—for example, in education for women or food availability—individual genetic predispositions become more significant differentiators, leading to genetically-driven inequality.