How fragile is our intellect? Estimating losses in general intelligence due to both selection and mutation accumulation

Two dysgenic models of declining general intelligence have been proposed. The first posits that since the Industrial Revolution those with low g have had a reproductive advantage over those with high g. The secondposits that relaxed purifying selection against deleteriousmutations inmodernpopulations has led to g declining due to mutation accumulation. Here, a meta-analytic estimate of the decline due to selection is computed across nine US and UK studies, revealing a loss of .39 points per decade (combined N = 202,924). By combining findings from a high-precision study of the effects of paternal age on offspring gwith a study of paternal age and offspring de novomutation numbers, it is proposed that, 70 de novomutations per familial generation should reduce offspring g by 2.94 points, or .84 points per decade. Combining the selection and mutation accumulation losses yields a potential overall dysgenic loss of 1.23 points per decade,withupper and lowerboundvalues ranging from1.92 to .53points per decade. This estimate is close to those from studies employing the secular slowing of simple reaction time as a potential indicator of declining g, consistent with predictions that mutation accumulation may play a role in these findings. 2014 Elsevier Ltd. All rights reserved.