Epidemiological studies suggest that educational attainment is affected by genetic variants. Results from recent genetic studies allow us to construct a score from a person’s genotypes that captures a portion of this genetic component. Using data from Iceland that include a substantial fraction of the population we show that individuals with high scores tend to have fewer children, mainly because they have children later in life. Consequently, the average score has been decreasing over time in the population. The rate of decrease is small per generation but marked on an evolutionary timescale. Another important observation is that the association between the score and fertility remains highly significant after adjusting for the educational attainment of the individuals.
Epidemiological and genetic association studies show that genetics play an important role in the attainment of education. Here, we investigate the effect of this genetic component on the reproductive history of 109,120 Icelanders and the consequent impact on the gene pool over time. We show that an educational attainment polygenic score, POLYEDU, constructed from results of a recent study is associated with delayed reproduction (P < 10−100) and fewer children overall. The effect is stronger for women and remains highly significant after adjusting for educational attainment. Based on 129,808 Icelanders born between 1910 and 1990, we find that the average POLYEDU has been declining at a rate of ∼0.010 standard units per decade, which is substantial on an evolutionary timescale. Most importantly, because POLYEDU only captures a fraction of the overall underlying genetic component the latter could be declining at a rate that is two to three times faster.
Epidemiological studies have estimated that the genetic component of educational attainment can account for as much as 40% of the trait variance (1). Recent meta-analyses (2, 3) yielded sequence variants contributing to the underlying genetic component. A negative correlation between educational attainment and number of children has been observed in many populations (4⇓⇓–7). A recent study of ∼20,000 genotyped Americans born between 1931 and 1953 provided direct evidence that the genetic propensity for educational attainment is associated with reduced fertility (8, 9), supporting previously postulated notions (10) that the population average of the genetic propensity for educational attainment and related traits must be declining. Here, using a population-wide sample that is both much larger and covers a substantially greater time span, and with additional auxiliary information, we aim to estimate the change of the genetic propensity of educational attainment in the Icelandic population over the last few decades, starting with an in-depth investigation of the relationship between a measurable genetic component of educational attainment and various aspects of reproduction (11⇓⇓–14).
Researchers say that while the effect corresponds to a small drop in IQ per decade, over centuries the impact could be profound
Spending longer in education and the career opportunities that provides is not the sole reason that better educated people tend to start families later and have fewer children, the study suggests. Many people who carried lots of genes for prolonged education left the system early and yet still had fewer children that the others. “It isn’t the case that education, or the career opportunities it provides, prevents you from having more children,” said Kari Stefansson, who led the study. “If you are genetically predisposed to have a lot of education, you are also predisposed to have fewer children.”
But the effect is very small. Writing in the Proceedings of the National Academy of Sciences the researchers estimate that it corresponds to a drop in IQ of about 0.04 points per decade. If all the genes that contribute to education were included, they add, that figure might rise to 0.3 points per decade. Nevertheless, Stefansson believes that if the trend continued for centuries, the impact could be serious.