It is a profound mystery how evolution hardcodes abstract social desires (e.g., reputation) into our genome. Unlike simple sensory rewards, these require complex cognitive processing to even identify. Solving this could unlock powerful new methods for instilling robust, high-level values in AI systems.

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.

Decades of twin studies reveal that, on average, all psychological traits are about 50% heritable. Crucially, when it comes to pathological personality traits found in disorders, the heritability rate actually exceeds this 50% baseline, indicating a stronger genetic influence for these extreme conditions.

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.

The TYK2 gene variant, a risk factor for tuberculosis, increased in frequency for thousands of years before plummeting in the last 3,000. This suggests it protected against an earlier threat but became a liability with the rise of endemic tuberculosis in denser populations, showing how selection can reverse direction.