Science News / All In The Family
Could there be genetic benefits to marrying distant cousins for animals and humans?
It's no secret that humans interbreed too. Charles Darwin married his first cousin, Emma Wedgewood. More recently, a 1997 study of Pakistani hospitals found that three out of five marriages were between first cousins, while a study of one South Indian city found that one-fifth of marriages occurred between uncles and nieces and a third between first cousins.
But close inbreeding comes with a high cost for humans. "First cousins, when they have babies—it's like a textbook example—tend to have higher mortality," Zamudio says. In contrast, scientists know little about the effects of inbreeding between more distantly related couples—third cousins and beyond. But recent work on Icelanders suggests that some family loving might be a good thing.
A team of researchers at the Icelandic firm deCODE genetics sifted through 165 years of genealogy data from 160,000 couples. Pairs who shared a great-great-grandparent—third cousins—tended to have more children and grandchildren than did more distantly related spouses. For instance, women born between 1925 and 1949 who married third cousins had 3.3 kids and 6.6 grandkids, on average. Women who married eighth cousins bore 2.5 children and 4.9 grandchildren. Yet the study, published in the Feb. 8 Science, doesn't give carte blanche to forbidden love. More closely related couples—first and second cousins—had fewer children than less-related couples, and the inbred kids died at a younger age.
"That was a very nice confirmation of work people have done with other animals," says Bateson, who showed in the 1970s that Japanese quail prefer first cousins over brothers and sisters and over less-related birds. He and other researchers stress that animals in the wild must balance the pluses and minuses of inbreeding and outbreeding to do best for their children.