"Scientists Find Mammal Species that Practices Incest Frequently"

Scientists say a type of banded mongoose living in Uganda has one of the highest rates of incest of any mammal species, and the reasons behind that rate aren't entirely clear. For the most part, mammals avoid incest and inbreeding, since it tends to cause a drop in fitness, with offspring of incestuous mating often suffering from health problems, a team of British and German researchers points out. Groups of banded mongoose living in Uganda's Queen Elizabeth National Park are apparently an exception, the researchers say in their study published in the journal Biology Letters.

The researchers followed 14 mongoose groups resident in the park -- an average group is a close-knit gathering of around 18 adults -- and found most had dominant male and female members doing most of the mating, while animals on the fringes of the group seldom mated. The close-knit nature of the groups has resulted in an elevated rate of incest, the researchers found; 63.6 percent of newborn mongoose pups were the outcome of mating between two members of the same social natal group.

The high rated of incest may be linked to the dynamics of mongoose grouping, the researchers suggest. Newly formed groups have mortality rates three times as high as established groups, and any mongoose that attempts to move into a new group is generally turned away, often violently, they say. The result, they suggest, is that the animals have learned that with little opportunity for dispersal it's safer to mate with a close relative within a group than risk death by venturing out into the world to find a mate. For mongooses, apparently, the genetic problems caused by inbreeding are acceptable as a less dangerous choice than leaving the pack in search of new mates.

Within the Uganda mongoose bands male mongooses were observed mating with their daughters, the researchers report, but there were no such mating observed between females and their sons. That's not really a surprise, they say; males take much longer to reach sexual maturity than females, who have shorter lives and generally die before their own male offspring are old enough to mate with them.

This isn't all that surprising. Every time such evidence comes out, everybody's flabbergasted because they're not paying attention to all the other cases. As genetic studies of animal mating patterns improve, we'll likely find more and more cases like this.

Endogamy is a risky proposition, but everything in life is. The question for everything in evolution is: how risky, and for what reward? Endogamy and exogamy are just mating strategies. How often a species practices endogamy is related to the specific evolutionary circumstances of that species, including the social environment, which determine if and when mating with a close relative is worth the gamble. For some species the cost is too high. For others, it's not. And for still others, it's in between. I wonder where humans fall on that spectrum?