Evidence analysis shows that animals rarely avoid inbreeding

The study demonstrates that animals rarely attempt to avoid mating with relatives, a finding that was consistent across a wide range of conditions and experimental approaches. Wolves were among the species studied. Photo: Eric Dufour/Mostphotos

Humans consider inbreeding in animals is bad and should be avoided under all circumstances, but researchers suggest there is little to support this assumption.

The idea that animals should avoid mating with relatives has been the starting point for hundreds of scientific studies performed among many species. But it turns out the picture is more complicated.

“People assume that animals should avoid mating with a relative when given the chance,” says Raïssa de Boer, a researcher in zoology at Stockholm University.

However, evolutionary theory has, for more than four decades, been indicating that animals should tolerate, or even prefer, mating with relatives under a broad range of conditions.

Fresh research carried out at Stockholm University and published in Nature Ecology and Evolution examined the results of 139 experimental studies in 88 species spanning 40 years of research.

The work settles the longstanding debate between theoretical and empirical expectations about if and when animals should avoid inbreeding.

“We address the ‘elephant in the room’ of inbreeding avoidance studies by overturning the widespread assumption that animals will avoid inbreeding whenever possible”, she says.

The study demonstrates that animals rarely attempt to avoid mating with relatives, a finding that was consistent across a wide range of conditions and experimental approaches.

“Animals don’t seem to care if their potential partner is a brother, sister, cousin or an unrelated individual when they are choosing who to mate with”, says Regina Vega Trejo, a researcher at Stockholm University and an author of the paper.

The study also looked at inbreeding avoidance in humans, comparing the results with similar experiments with animals.

“We compared studies that asked if humans avoid inbreeding when presented with pictures of faces that were digitally manipulated to make the faces look either more or less related to studies that used similar approaches in other animals. Just like other animals, it turns out that there is no evidence that humans prefer to avoid inbreeding,” de Boer says.

John Fitzpatrick, an associate professor in Zoology at Stockholm University and the senior author of the study, said the findings help explain why many studies failed to find clear support for inbreeding avoidance.

The study, he says, offers a useful roadmap to better understand how cognitive and ecologically relevant factors shape inbreeding avoidance strategies in animals.

The findings are likely to have wide-reaching implications for conservation biology. Mate choices are increasingly being used in conservation breeding programs in an attempt to bolster the success of conservation efforts for endangered species. What does this mean?

“A primary goal of conservation efforts is to maintain genetic diversity, and mate choice is generally expected to achieve this goal,” Kirkpatrick says. “Our findings urge caution in the application of mate choice in conservation programs.”

de Boer, R.A., Vega-Trejo, R., Kotrschal, A. et al. Meta-analytic evidence that animals rarely avoid inbreeding. Nat Ecol Evol (2021). https://doi.org/10.1038/s41559-021-01453-9



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