Why Marrying Your Cousin May Pay Off

In 2014 Live Science had an article about cousin marriage:

Yet some research suggests an alternative perspective. "There's this counterintuitive finding that higher spousal relatedness is related to higher reproductive success in several humans societies," said Drew Bailey, a psychologist at Carnegie Mellon University in Pittsburgh, and co-author of the study detailed May 21 in the journal Biology Letters.

Even in modern, industrialized society, research suggests that people tend to marry others with similar DNA.

In line with previous findings, the researchers found that among non-foraging societies, a couple's relatedness was linked with having more surviving children. But among foraging societies, the opposite was true: More-closely related spouses had fewer surviving children.

Furthermore, the more family intermarriage in a society, the greater the benefit of intermarrying on the number of children couples had. In other words, in societies in which people frequently married their relatives, intermarrying showed a stronger link to having more children.

There could be many explanations for the different effects of inbreeding shown in the two kinds of societies. Perhaps the best explanation, Bailey said, may be that non-foraging societies are more likely to have heritable resources, such as wealth or livestock, so a tight-knit family group might be more likely to defend each other and their shared resources. By contrast, in a foraging society, it might make more sense to be part of a much larger, interconnected group, since there are few or no resources to be inherited.