An article by Anna Goodman and Ilona Koupil in last month’s Evolution and Human Behavior found a link between school performance and number of children and grandchildren (in Sweden 1915-1929). This effect, as might be expected, held in males only. The number of children was linked almost entirely to whether the male married, with marriage largely a function of socioeconomic position. As most males married (around 90%), the effect of schooling performance on number of children was largely evidenced in those males at the bottom of the distribution.
One observation made by Goodman and Koupil was that as marriage prospects were largely mediated by socioeconomic position, there was little evidence of selection for cognitive abilities per se. It could be interpreted as a cold hearted conclusion. While money and social position are clearly going to have influence, what of the effort put into conversation, humour and other displays of intelligence. Are they all for nought?
For the group in this particular study, it might be reasonable conclusion. However, given the differences are only at the low end of the school performance distribution, we might be seeing a threshold effect, whereby women are not interested in marrying someone below a certain standard. It reminds me of some of Bernard Salt’s work, whereby an eligible man is defined as someone not married, straight, not in jail and earning over $50,000 a year. They are not even in consideration.
From a selection point of view, the elimination of individuals at the bottom of the distribution has somewhat different consequences to different reproductive success across the full spectrum of performance. I am going to dig some more into the data over the next few days to get a feel for what the change in distribution might look like over time.