"Some studies have found the gains of the Flynn effect to be particularly concentrated at the lower end of the distribution." This immediately suggests the hyp

"Some studies have found the gains of the Flynn effect to be particularly concentrated at the lower end of the distribution." This immediately suggests the hypothesis that environmental improvements[1] have increased the likelihood of individuals reaching their genetic potential, which also explains why the top end remains unchanged—it was already near its ceiling. Of course there isn't a single "gene for intelligence"; each individual has different genes (parameters) leading to diverse tradeoffs and variations in (here) cognitive ability. But those genes can only manifest effectively if a person grows up with sufficient care. If nutrition, healthcare, exercise, and (possibly) education are lacking, then one cannot reach one's full theoretical potential. [1] Advances in public health (e.g., vaccination, hygiene), nutrition (reducing malnutrition), and education.