Science

Animals (including humans) would not be programmed to avoid inbreeding

Contrary to popular belief, animals rarely have strategies in place to avoid inbreeding, concludes a Swedish team in a review of work on the subject (meta-analysis) published in Nature Ecology and Evolution. Most would not need it, and some might even encourage it, in order to eliminate the bad qualities for survival instead of spreading them.

Animals do little to avoid inbreeding

Animals don’t seem to care if their potential mate is a sibling, cousin, or unrelated individual when choosing whom to mate with“, observes Regina Vega Trejo, researcher at Stockholm University and co-author of the article in a statement. The team she is part of analyzed 139 studies on 88 different species (including birds, rodents, fish and primates including human) and spanning 40 years of research on inbreeding in the animal world. Researchers quickly observe that there is a significant publication bias in favor of studies showing avoidance of inbreeding in the animals studied. after their statistical analyzes, “studies (…) which show a preference for a related partner are missing in the publication dossier“A bias that they attribute in part to our moral bias against inbreeding.

Despite “this clear evidence of publication bias“, their meta-analysis reveals that”there is little support for the widely held view that animals avoid mating with congeners“, conclude the authors.”On the contrary“, they add, kinship does not seem to be a key factor in mating in most of the animals observed, under experimental conditions. This conclusion seems logical in view of the researchers’ theoretical expectations:”theoretical models predict that parentage-unbiased mating should be common“, they expose.

The advantage of inbreeding

inbreeding, concludes a Swedish team in a review of work on the subject (meta-analysis) published in Nature Ecology and Evolution. Most would not need it, and some might even encourage it, in order to eliminate the bad qualities for survival instead of spreading them.

Animals do little to avoid inbreeding

Animals don’t seem to care if their potential mate is a sibling, cousin, or unrelated individual when choosing whom to mate with“, observes Regina Vega Trejo, researcher at Stockholm University and co-author of the article in a statement. The team she is part of analyzed 139 studies on 88 different species (including birds, rodents, fish and primates including human) and spanning 40 years of research on inbreeding in the animal world. Researchers quickly observe that there is a significant publication bias in favor of studies showing avoidance of inbreeding in the animals studied. after their statistical analyzes, “studies (…) which show a preference for a related partner are missing in the publication dossier“A bias that they attribute in part to our moral bias against inbreeding.

Despite “this clear evidence of publication bias“, their meta-analysis reveals that”there is little support for the widely held view that animals avoid mating with congeners“, conclude the authors.”On the contrary“, they add, kinship does not seem to be a key factor in mating in most of the animals observed, under experimental conditions. This conclusion seems logical in view of the researchers’ theoretical expectations:”theoretical models predict that parentage-unbiased mating should be common“, they expose.

The advantage of inbreeding

The reason is simple. Certainly, inbreeding can cause “inbreeding depression”, that is, cause the accumulation within the same individuals of restricted genetic characteristics, and increase the chances of the onset of disease or disability. The results of a severe inbreeding depression are for example visible in the old Habsburg family. Charles II, the last of his line, was ill, rickety and infertile. The rate of consanguinity between his parents then reached a record 25%, the equivalent of a brother and a sister, or a mother and a son.

But this inbreeding was voluntary, over several generations, and in humans. In other species, it may be that the living conditions are already sufficiently unfavorable for inbreeding that individuals do not have to develop a particular strategy to avoid it. For example, when people are very numerous or live in large areas, where they are unlikely to run into a cousin, and if so, have it happen again the next generation. Likewise, if the species in question generates significant offspring, then the inbreeding of some individuals will not prevent the species from surviving, and therefore individuals will not need to avoid inbreeding. “Our results underline the importance of quantifying inbreeding depression within the populations studied in order to better appreciate the inbreeding avoidance strategies.“, conclude the researchers.

It may even be that some species prefer inbreeding, say the scientists, because it allows the accumulation of potentially harmful genes in individuals doomed to die, instead of spreading them in the population. Despite this reasoning already known for several years, “the hypothesis that inbreeding avoidance is widespread in animals remains, possibly due to human moral judgment against incest“, interpret the authors in the publication.

Even in humans

It may even be that our own species is no better able to avoid inbreeding, outside of the moral framework that we have built around incest. The social context would have made it possible to avoid this risk by encouraging women to leave their original clan to procreate, according to several studies on our ancestors. Among the studies reviewed by the Swedish team, one involved presenting photos of potential partners to men and women, and asking them which they found most attractive. Some photos had been altered so that the face resembled the subject enough to evoke a family relationship. But the modified photos have had the same success as the others. “Just like with other animals, it turns out that there is no evidence that humans prefer to avoid inbreeding.“, concludes in a press release Raïssa de Boer, first author of the publication. And this, in spite of our”tendency to react with disgust to incest“, note the authors, who nevertheless concede the limits of this experience.”Measures of mate choice in humans were outside their natural context. “

We found no difference in avoidance of kinship between males and females, experiences with or without choice, mated animals and virgin animals or between humans and animals.“, finally conclude the researchers.

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