Just curious. Humans have complex social arrangements and to prevent this. How do animals manage to avoid incest and inbreeding?
As a second question, beyond animals in general, specifically how do the great apes prevent this?
Generally, animals that live in groups prevent inbreeding by kicking out the young males once they reach breeding age.
Simple and effective. A bit harsh, but hey.
Why do you think kids get sent off to college?
A lot of them don’t. In fact, it would be my WAG that *most * of them don’t. I know the fish in my fish tank don’t care, and cats don’t care. I hear dogs are the same way.
My mother used to live in an apartment complex with her cats, who went outside. One of them was a female, whose father was the big tomcat on the block.
Well, apparently the big tomcat gets to have his way with all the females, because he impregnated my mom’s cat, several times. One cat turned out to be extremely anti-social, if not mentally damaged, but lived with her anyway. Another litter had all the kittens eventually die, mostly due to the imbreeding. I wasn’t there to see it, but I was told that one kitten couldn’t move it’s back legs at all for weeks before it died.
So it implies that cats don’t care at all. But since the inbred ones end up dying pretty quickly anyway, it doesn’t really matter. Kind of like I’ve heard that the Ancient Egyption royalty used to marry brother to sister. Any kids who were obviously defective got a retroactive abortion.
Having been raised on a dairy, I can tell you there are a lot of bulls out there having mad bovine sex with their daughters and grand-daughters. Although in these days of AI (artificial insemination), chances are good that the bull and most of his offspring have never met.
Obviously, the answer is going to vary widely between species, ranging from complex social arrangements to a simple “they don’t”.
Heh, one of the few things I remember from high school bio: cheetahs are so inbred that they’re almost all identical.
http://lynx.uio.no/jon/lynx/cheetahg.htm
Some other links were talking about how it probably came about because of two big population crisis’.
I’m not at all certain that this is generally true. Amongst the great apes for example the norm is for the young females to be ‘kicked out’ and go an live with the family of unrelated males, and the human branch of the great ape family is generally no exception to that rule.
In addition to that type of arrangement we have the situation where the males and females live essentially separate lives and only come together briefly for mating as is the case for elephants, and the situations where the individuals of both sexes are essentially solitary by nature as is the case for most cats. Then of course there are numerous cases such as found amonst wolves where neither male nor female young are more likekly to be expelled.
In short I’d have to see some sort of evidence before I’d accept that animals generally expel the young males. Intuitively I’d say they generally don’t.
Having said that I suspect that the general principle is sound. Most animals have some form of dispersal mechanism that more or less gurantess that inbreeding won’t continue for generations. The consequences of inbreeding are not as dire as people generally assume and usually only become seriously problematic after continuous line breeding for several generations. So long as some sort of dispersal occurs to bring in fresh blood periodically it’s not really a problam.
So a gorilla may well mate with his own duagther, but he will also inevitably mate with unrelated females from neighbouring tribes. That ensures that fresh blood is constantly being added to the tribe and through pure chance within a few generations the dominant male will be one of his progeny from an unrelated female and hence inbreeding will have ended. In fact such a process will be accelerated as soon as inbreeding produces any detrimental effects since only males not suffering from the defects will rise to dominance. As a reuslt inbreeding will be at worst a nusiance.
The same priniciple applies to cats, where a tom will only win out in fights for mating rights with his own daughters/granddaughers for a few generations before an unrelated rival wins his territory and so on for the various other arrangements.
IOW so long as some animals are moving away form their own family members and so long as competetion for mates exists there is automatically a mechanism to prevent inbreeding.
BTW, there is more involved in human avoidance of inbreeding than social customs. People put great selective value on mates that are not deemed to be close relatives and the selection seems to have little to do with culture or even conscious choice. It’s entirely possible that similar instincts exist in other animals.
The Ngorongoro lions are an example of a group that is significantly inbred because of their small numbers and isolation from other groups.
Woman is afraid her female cat has a tumor, so she has the vet make a house call. Vet informs her the cat is simply pregnant.
Woman: That’s impossible. She never goes out.
Vet: Isn’t that a male cat on that chair?
Woman: But that’s her brother!
I can’t find a cite now, but I’ve always heard that straight line breeding (fathers impregnating daughters) doesn’t produce the defects that brother sister crosses do. So with dominate males getting most of the ‘rights’ and with short lifespans of lots of wild animals, it (the bad interbreeding) may just not actual happen very much.
-rainy
You can’t base anything on the behavior of domestic animals, or animals in captivity. If animals don’t have a choice, or don’t have much of one, most will mate with offspring or siblings.
Research has demonstrated that some animals, in particular some rodents, are able to recognize kin (apparently through olfactory signals) and avoid breeding with them. One example is here. (Warning: pdf) Many others can be found by googling “inbreeding avoidance mate choice.”
As has been said, in many animals, whether social or solitary, one sex or the other typically disperses from the social group or the territory in which they were born. This is probably the most common mechanism for incest/inbreeding avoidance. However, other mechanisms exist for kin recognition and the avoidance of inbreeding.
Amish???
A better example might be middle eastern cultures, which have high levels of cousing marrying - in Saudi Arabia, for example, 41% of people are married to their second cousin or closer relative.
It may not be incestual inbreeding, but limited mate selection and a small population leads to a raft of genetic diseases that affect the Amish.
Another possible example would in fact be humans; women can according to some studies detect how similar the major histocompatibility complex of a man is to that of her father by scent, and tend to find the scent of males with highly similar MHCs a turn off.
I can’t agree with any of this.
Surely inbreeding is something that limits the gene pool over many successive generations, and doesn’t at all mean that an entire litter will die because of “inbreeding.” Limiting the gene pool potentially makes offspring more susceptible to disease, or malformations, if a gene or set of genes is missing. It’s not an instant killer.
What would this have to do with it? Either the animal lives long enough to propagate or doesn’t; once the animal has propagated, dying won’t undo the genetic legacy.
I remember reading once about the cultural result of kibbutz life in Israel; some psychologist observed that guys were less interested in the girls they were raised with than with strangers. Unrelated children are raised in an almost communal lifestyle as close as brothers and sisters - and the theory was that there’s an instinctive desire for strangers instead. (Of course, like any human urge, the rule is never 100%).
For solitary wandering animals, the general pattern of dispersal probably helps prevent long-term inbreeding. For harem-pattern breeding and expelled males, the requirement that the dominant male come from the outside (old enough) and defeat the current dominant male helps ensure that the male is healthy and that there is a decent chance it is a stranger to the herd. I guess it depends how far the solitary males wander.
For giant flocks, schools, whatever - sheer population size and random pairing would ensure that the odds are low that any incest would be more than a single occurence.