While the thought of searching for a potential mate at a family reunion might sound repulsive to some, researchers in Iceland report that “kissing cousins” may produce more children and grandchildren than unrelated couples. A study released Thursday in the journal Science found that marriages between third or fourth cousins in Iceland tended to produce more children and grandchildren than those between completely unrelated individuals.
Researchers at the deCODE Genetics company in Reykjavik mapped out kinship among all known Icelandic couples whose members were born between 1800 and 1965. They then compared the numbers of children and grandchildren descended from these 160,811 couples. Researchers were shocked to find that for women born between 1800 and 1824, marriages between third cousins produced an average of 4.04 children and 9.17 grandchildren, while marriages between eighth cousins or more distantly related couples had averages of only 3.34 children and 7.31 grandchildren. For women born between 1925 and 1949, with mates related at the degree of third cousins, the average number of children and grandchildren were 3.27 and 6.64, compared with 2.45 and 4.86 for those with mates who were eighth cousins, or more distantly related.
“These are counterintuitive, almost dislikable results,” said Dr. Kari Stefansson, senior author of the paper on the study. Dislikable, because our intuition is that the more closely related you are to your mate, the higher the chances of passing along the unfortunate traits so often associated with inbreeding. Researchers believe the trend toward a more prodigious relationship with a not-so-distant relative must have a biological basis, though scientists have not identified exactly what biological mechanism could be behind this.
[…] Marriage, it turns out, is not an exact science. For example, a 1991 study also published in Science found that, in Asian and African populations, marriages between related individuals also produced more offspring. However, researchers only evaluated relationships no more distant than second cousins, and the populations they studied showed great socioeconomic disparity. In the most recent study, researchers sought to eliminate some of these confounders by limiting their study to only the Icelandic population — a country of relative socioeconomic homogeneity, where there is little variation in family size, use of contraceptives, or marriage practices. […] According to Stefansson, these results are particularly striking in their consistency throughout time, even as socioeconomic factors in Iceland began to change.
Results showed that marriages between third or fourth cousins produced more offspring than unrelated couples from the years when Iceland was a predominantly poor and rural country up until the present-day era of a highly urbanized society, with one of the highest standards of living in the world. Now, many gene experts are scratching their heads while trying to explain the biological mechanism behind these results. […] According to Stefansson, the reason that related couples were more biologically successful may be because these couples have “just right” genes when combined — not too similar, but not too dissimilar, either.
[…] However, Buehler added he “can’t think of any genetic explanation for why the third or fourth cousins would have more babies.” Instead, Buehler supposed that related couples might shack up more often, simply because of pheromones. “Maybe what we’re seeing here is biologic attraction,” Buehler said. “If you really look alike, feel alike and think alike, then maybe you have sex more often and have more babies. We do know that there are pheromones which cause attraction, and I wouldn’t be surprised if related people have higher sexual desire for one another.”
But despite the inability to offer a concrete biological explanation for these findings, Stefansson strongly believes this study has implications on the genetic future of the global population. “The take-home message is that … we, as a society of [the] 21st century, have basically ruled against the marriages of closely related couples, because we do not look at it as desirable that closely related people have children,” Stefansson said. “But in spite of the fact that bringing together two alleles of a recessive trait may be bad, there is clearly some biological wisdom in the union of relatively closely related people.”
I currently live with my half-brother/husband, as I have for the last five years and our [4-year-old] son. […] My oldest son lives with us […]. In 2013, the court granted us joint custody of three of my husband’s grandchildren and, later, a baby. [The kids] all know that we are in a relationship and have never asked any questions. They are happy, doing well in school, and are overall well-adjusted.
[…] Our relationship has been both romantic and sexual since April 2010. He is older than me by 28 years. Our dad got started early and quit late. [laughs] […] [My mother] disliked my brother the most and frequently spoke badly of him to me whenever I would ask about him. I saw him only twice that I remember growing up. Once when I was around three or four, and again when I was around eleven or twelve. Both were very brief meetings. […] Other than that, my childhood was pretty normal until my dad died when I was fifteen and my mom kicked me out a year later. She went kind of crazy for a while but I don’t hold that against her.
[…] When I was 19 my sister asked if I wanted to go see him. I was so excited to finally be able to spend time with my brother. But when we pulled up and I saw him standing outside I immediately thought, “He is so hot. I want to be with him. Too bad he’s my brother.” When I stepped out of the car though, our eyes met and I was certain by the look in his eyes that he was feeling the same thing I was feeling. So I had some idea that it could turn sexual, and I certainly hoped it would, but I couldn’t be 100% sure.
We started talking and texting every day. He would come pick me up and we would go out to lunch or to a local lake park and hang out by the water. It was wonderful. I made the remark once or twice to friends that I felt like I was dating my brother. I even stayed the night a couple of times. […] We would cuddle in bed and months later he even told me, “I knew that first time that you spent the night and you laid your head on my chest and put your arm across me the way a woman does a man that I was in trouble.”
After about three weeks of texts that others would have sworn were between long lost lovers, a couple of sleepovers, and seeing each other nearly every day, the talk came. He sent me a text that saying that he loved me and I said I love him too. He said “No, I think I love you more than I should.” I just replied, “I know. I think I love you more than I should too.”
[…] We agreed that he would pick me up that Saturday and take me to a fireworks show, and we would see what happened then. We cuddled together, held hands, and watched the fireworks. When we got to the car we just leaned in at the same time and kissed each other. We had a pretty heavy make out session and then he took me home. I called him before he even left my neighborhood and told him to come back and get me. I missed him terribly already. He picked me up, I went home with him […]. I moved in with him two weeks later and we have been together ever since.
[…] Prior to this, I had never been sexually attracted to any of my family, but one of my cousins asked me out once when I was eleven. When I was 17, two of my first cousins started dating and I saw no issue with it. They were happy, and that was what mattered. They now have two healthy children together and have been living as husband and wife for at least seven years. […] I probably know more people like us, they just haven’t revealed it.
[…] We have one son together, unplanned but not unwanted, and he is perfectly healthy and very smart. […] We want a little girl and had planned on trying, but then we had to take custody of the other kids and it’s not affordable anymore. If the other kids ever get to go back to their mom, then we are definitely going to try. We have discussed going on and trying now anyway.
[…] Our dad’s family is perfectly OK with it and even supportive. They were even excited to see our son when they met him. My sister knows and is also very supportive. Even my oldest son’s father knows and he is fine with it. He has become a good friend and I talk to him when I need someone different to listen. I recently told my mom and she has nothing but bad things to say to me so we are not speaking at this point. She is trying to make me choose, but she doesn’t seem to realize that if she does, she is going to lose every time. I refuse to give up my life, happiness, family, and the greatest love I have ever known just to please someone else. […] We are very blessed and we do not take this for granted. We act like a couple everywhere we go because anyone that matters now knows. Everyone else just assumes we are a normal couple.
[…] Maybe [critics] should try to just not love the person they are with and see how that works out for them. No one is preying on anyone in this relationship. I wanted him as soon as I saw him, and he felt the same way. […] It is not our faults that we never got to build that familial bond with one another, and it is not our faults that we still don’t feel that bond. Don’t get me wrong, I fully support non-GSA consanguineous couples as well, but I think the laws are exceptionally ridiculous to criminalize GSA consanguineous couples because of all of the broken homes, unplanned pregnancies, and egg and sperm donations we have today.
[…] I want nothing more than to marry the man I love. I never thought I could love or be loved as much as I have the in last five years. I’m sure there are many more years to come. […] He is the love of my life and I couldn’t have built a better husband for me or father for our son. […] We still talk about marriage though and will likely have some type of ceremony of our own.