Do wild animals avoid incest?

13 February 2011

Question

Hello,

Inbreeding is a very bad idea from an evolutionary point of view, which leads you to think that powerful mechanisms should have been evolved to limit its occurrence. Humans have created cultural taboos against it, but lacking this possibility how do wild animals do to avoid breeding among close relatives?

Regards

Claes

Answer

Diana - There are a few adaptations. One interesting one is hyenas. Apparently, female hyenas will only breed with males that have been recently born into their group or who have just recently joined it. And male hyenas will only move to new groups of females to breed. So they've got a sort of social setup which helps to avoid incest. But, on a more sort of scientific level, lemurs actually use scent. They use pheromones on their naughty bits to detect who is the most closely related to them and who's the farthest sort of relation. The females who will actually smell the males and decide "he seems perhaps a bit of a close relative. I'm not going to go there." but I think Chris, isn't there also something about mice?

Chris - Well, mice are intriguing. The explanation for mice is that the genes which are concerned with smell are found on the same part of the genome as the genes that control how the immune system decorates cells so they can recognise each other. The idea is that if mice smell alike, they probably have a very similar immune system as well. The problem with this is that if you have an immune system that's too similar, it shows you're very genetically related and so, if you have your smell system programmed to recognise someone who's very closely related to you, it means it's a bad idea to mate with them. People have done experiments: If you take a male mouse and a female mouse, and they're brother and sister, if you force them and you put them in a caged environment where they haven't got any choice, then they will mate with each other and have offspring. But if you introduce a second mouse, so you've got the mouse's brother and then another male mouse that's unrelated, then the female mouse will preferentially mate with the one she's not related to. And if you introduce the second male mouse after the mouse is already mated and is already pregnant, she can abort the pregnancy and then mate with the new mouse. So, they are very strongly trying to avoid incest at all cost, it would appear.

Diana - Yeah, that's interesting. I think it's probably worth mentioning but sometimes it happens the other way. The ancient Egyptian royal family actually used to promote incest because they thought it was a good thing.

Chris - But were there consequences? Presumably there were.

Diana - There were, and Tutankhamun, of course, famously had a club foot as a result.

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