It’s a common perception that less-educated people have more children. The idea causes much hand-wringing and gnashing of teeth over the possibility that human populations might become stupider over the course of generations. But it’s actually pretty difficult to confirm whether there really is a reproductive trend that would change the genetic makeup of the human population overall.
Jonathan Beauchamp, a “genoeconomist” at Harvard, is interested in questions at the intersection of genetics and economics. He published a paper in PNAS this week that provides some of the first evidence of evolution at the genetic level in a reasonably contemporary human population. One of his main findings is slight evolutionary selection for lower education—but it’s really slight, just 1.5 months less of education per generation. Given that the last century has seen vastly increased education across the globe, and around two years extra per generation in the same time period as Beauchamp’s study, this genetic selection is easily outweighed by cultural factors.
There are other important caveats to the finding, most notably that Beauchamp only looks at a very small segment of the global population: US citizens of European descent, born between 1931 and 1953. This means that we can’t generalize the results to, say, China or Ghana, or even US citizens of non-European descent.
Based on this data, we also can’t say whether people who have been of reproductive age at different times are subject to similar forces. An evolutionary force that changes the course of our species would need to be multi-generational, and this study doesn’t have evidence of that. “The time span covered by Beauchamp is too short to shed light on this question,” write Alexandre Courtiol, Felix C. Tropf, and Melinda C. Mills in a PNAS commentary on Beauchamp’s project.
So why is it interesting? Well, it’s one of the first forays into evolution in the contemporary human genome. There has long been some muttering about whether humans are still evolving. David Attenborough, for instance, has said that we’re not: “We stopped natural selection as soon as we started being able to rear 95–99 percent of our babies that are born,” he told Radio Times in an interview.
He was clearly wrong, though. Even if most people survive into adulthood, evolution cares about one thing, and one thing only: offspring. If people with certain genes have more children than people with other genes, those genes proliferate, and that’s evolution. Prior to the explosion in genetic data that’s currently underway, however, we didn't have the data to say much about it.
Watching our genomes evolve
Previously, there have been studies exploring how modern humans might be evolving, but those studies haven’t used genetic data. They focused on a population, asking how many children people in that population group have and whether certain characteristics are related to having more or fewer children. Of course, it’s important that the studies focus on characteristics where genetics play a role. For instance, we know that genes (along with nutrition) play a role in height, so if tall people have more children, we can assume that those genes are becoming more common.
The problem with these studies is that they don’t look at the genome itself. Evolution only happens when certain genes are associated with having more children; in order to find evidence of that evolution, it’s essential to go digging around in the genome.
That’s what Beauchamp did, and he was one of the very first to do it, along with another group of researchers who published a paper earlier this year. Their study looked at who people choose to marry and reproduction across population groups. The data Beauchamp used suggested that the effect on education was driven largely by people who had no children at all, rather than by the difference between small and large numbers of children.
It’s still a mystery what might be driving this effect. There’s a huge amount we don’t understand about the links between genes and people’s actual characteristics, note Courtiol, Tropf, and Mills. People’s educational attainment does depend partly on genetic traits, like intelligence and conscientiousness, but it’s still unclear what exactly the genetic markers associated with education are really doing when they help build and run a human. It’s possible they’re influencing a number of different traits, and we don’t know which of those results in people having more children.
The conclusion is tentative, but “the approach is very interesting,” says Yair Field, a genetics researcher at Stanford. “Given the growing availability of [data], this line of research is likely to be followed and extended by further work in the near future.”
“These studies mark a milestone in our understanding of human evolution and natural selection in contemporary populations,” write Courtiol, Tropf, and Mills. What would be ideal, they say, is to have multi-generational studies that really allow us to see whether certain genetic traits are becoming common in each successive generation. This would be incredibly tricky—studies like these need large amounts of nice, clean data, a better grasp of how genes affect traits, and a good grasp on the role of culture. Still, they write, “the question now shifts from whether or not natural selection is present to an examination of its effects.”
This post originated on Ars Technica