Could Cupid's arrow be laced with secret instructions for decoding someone's DNA? As this ScienCentral News video reports, researchers have found a connection between romance, genetics, and even a couple's sex life.
Love is a mysterious thing and never easily explained. Now an evolutionary psychologist has shown that true romance requires a special kind of chemistry. Literally.
"I think that these findings really get at one of Cupid's tricks," says Christine Garver-Apgar of the University of New Mexico. "We don't know all of his tricks but this study is one of the first studies that gives us a specific mechanism to define romantic chemistry. It tells us what it is about two individuals that just makes two people crazy about each other."
Garver-Apgar gave 48 romantically involved heterosexual couples questionnaires that measured aspects of their relationships and sex lives. She also took DNA samples to test how similar or different the couples were in a specific area of the genome, called the major histocompatibility complex, or MHC. As she wrote in the journal Psychological Science, if their genes in this area were very similar, there was a greater chance of trouble in paradise.
"The more genes that a couple shares in this particular family of genes, the more men and women reported that women were less sexually satisfied with their partners, they were more sexually attracted to men outside of their current relationship, particularly when they were nearing ovulation, and they actually reported having more extra-pair sexual partners during the course of their relationship ... in other words, the more they were cheating on their current partner," says Garver-Apgar.
The MHC is involved with immune system function. The molecules created by this section of the genome are present on the surface of every cell in our body, and serve as warning scouts that detect invaders. Essentially, they differentiate between "self" and "non-self" molecules; when something is recognized as non-self, the immune system may be called into action.
Garver-Apgar says partnering with someone whose immune system is genetically different than yours makes perfect sense from an evolutionary perspective.
"If you choose to mate with somebody who is genetically dissimilar from yourself at these particular genes or any other genes, you increase the genetic variability of your children so you are avoiding inbreeding in a sense," she says, adding that variety in the MHC genes likely strengthens the immune system. "You may ensure that your children have an immunological advantage. So they may be buffered [against] a wider variety of pathogens and toxins. And in an ancestral environment this would have been very, very important."
Previous studies have shown that various animals (mice, birds, and fish) prefer mates with dissimilar MHCs to theirs. Previous studies with human volunteers showed that women tend the prefer the scent of opposite sex individuals who have dissimilar MHCs. "If you have men wear t-shirts for two days, and then you have women smell these t-shirts, they actually rate the t-shirts that were worn by men who are dissimilar from themselves at this particular family of genes as being more sexually attractive," explains Garver-Apgar.
She also took DNA samples to test how similar or different the couples were in a specific area of the genome. The study also suggests that people may be able to unconsciously pick up on these genetic differences through scent.
"We don't know the exact mechanism," says Garver-Apgar. "But what we do know is that these molecules are expressed on the surface of all of our cells, and they're shed from our cells, and then they become available for scent detection in bodily fluids like sweat and urine and saliva. So we do know that MHC molecules do play a role in the scent of an individual."
And while all this research may not give the most romantic spin to what's usually considered a matter of the heart, it does support the old saying that opposites attract.
Garver-Apgar's study was published in the October 2006 issue of Psychological Science and was funded by the National Science Foundation.
By Brad Kloza