In business, in science and in life, even cherished assumptions can be wrong

I am forever stressing to my clients, and those in workshops which I lead, the importance of testing all assumptions, no matter how deeply ingrained in yourself, the organization or society at large.

It’s for this reason that I love studies which explode societal, scientific and medical assumptions—especially those that have been around for a long time and are accepted as true even when hard evidence for them is missing.

One such assumption is that animals—including human animals—naturally avoid mating with relatives. This notion has been the starting point for hundreds of scientific studies performed among many species. But new research, published in Nature Ecology and Evolution, shows that there is little scientific support for this assumption.

What the researchers say: “People assume that animals should avoid mating with a relative when given the chance,” said the lead author. “But evolutionary theory has been telling us that animals should tolerate, or even prefer, mating with relatives under a broad range of conditions for more than four decades.”

The study provides a synthesis of 139 experimental studies in 88 species spanning 40 years of research. In total the findings seem to settle 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,” he added. In fact, 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,” said a co-author.

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 and just like other animals, it turns out that there is no evidence that humans prefer to avoid inbreeding,” the researchers wrote.

“Our findings help explain why many studies failed to find clear support for the inbreeding avoidance and offer a useful roadmap to better understand how cognitive and ecologically relevant factors shape inbreeding avoidance strategies in animals,” said the senior researcher.

The findings will have wide reaching implications for conservation biology. Mate choice is increasingly being used in conservation breeding programs in an attempt to preserve endangered species.

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

So, what? This study should not really be so shocking. We have known for millennia that the ancient Egyptians and Peruvians accepted what we would see as incestuous relationships as normal. Both were highly successful societies. Many hunter-gatherer societies do not frown on it (including the people I lived with for a year). There is very little hard medical or psychological evidence that voluntary near-kin mating is harmful or that the resulting children—if there are any—are in anyway abnormal. I stress “voluntary” because any incestuous act which is involuntary or is the result of a power imbalance (father/daughter for example) or coercion will cause lasting psychiatric harm.

Recent studies—reported in previous TR editions—have shown that up to 25% of all children born are not sired by the woman’s husband or long-term partner. Other research has shown that the percentage is roughly the same in pair-bonded animals.  It has always been assumed that the human babies were the result of adulterous liaisons with non-related males, but some evidence has recently pointed to the fact that near relatives might be responsible for a considerable percentage of these pregnancies.