Researchers have long understood that humans mate assortatively – that is, we select partners whose traits closely resemble our own. Education, socioeconomic status, religion, geography and other background traits predict which individuals will pair off. This has been viewed as a matter of “social homogamy.” That is, we tend to associate with and date people who are in our social orbit.
A new study Assortative Mating on Educational Attainment by a group of British and Dutch economists and psychologists suggests something more biological – that the preference for a mate of similar intelligence is part of our DNA. The researchers examined the genomes of 1,600 married couples in the UK and found “molecular genetic evidence for assortative mating” with respect to education. Put in simpler – and starker – terms, assortative mating shifts the genetic pool away from diversity. At its most extreme, we would call this increased homogeneity inbreeding.
Lead author and economist David Hugh-Jones expressed concern to the Daily Mail about the implications:
“Our findings show strong evidence for the presence of genetic assortative mating for education in the UK. The consequences of assortative mating on education and cognitive abilities are relevant for society. They are also relevant for the genetic make-up and therefore the evolutionary development of subsequent generations.”
This growing tendency in human mating produces a “genetic wealth gap”:
“Assortative mating on heritable traits that are indicative of socio-economic status, such as educational attainment, increases genetic variance in such a way that the inequality in genetic capital grows.
When growing social inequality is (partly) driven by a growing biological inequality, inequalities in society may be harder to overcome. Effects of assortative mating may accumulate with each generation.”
The Women’s Movement has played a key role in the trend toward more assortative mating. Historically, women have been generally unwilling to marry men with fewer intellectual or monetary resources than themselves. Since female educational attainment is currently outpacing male attainment, the pool of marriageable men has shrunk relative to the female population.
“The increasing social mobility for females during the second half of the 20th century possibly also led to an increase in assortative mating as well as an increase in social inequality (Greenwood et al., 2014; Schwartz, 2013).”
In addition, the shift from a society of one-earner households to two-income households has effectively doubled the effect; the educated working couple is much better off than a family with one earner, less educated working couples, or singles.
Indeed, a study of assortative mating in the U.S. between 1960 and 2005 found that assortative mating increased income inequality. (Greenwood, J., Guner, N., Kocharkov, G., & Santos, C. (2014)
“The researchers tested whether their results emerged from other factors, such as partners meeting simply because they lived in the same place. They re-matched individuals with random partners within the same educational levels and locales. But the scientists found that the genetic scores of random couples were far lower than those of the originals.
This, the researchers say, lends strong support for their theory: two people genetically hardwired for good grades are drawn to one another, regardless of where they are from.”
I have no easy solutions to propose. We obviously can’t (and wouldn’t want to) legislate mating. But we do need to be aware that inequality – both genetic and income – is on the rise. Society is moving rapidly toward a true polarization of haves and have-nots.