Once upon a time, there was a meadow vole who was quite promiscuous in his behavior. He would mate with several voles and practically ignore his children. His cousin, the prairie vole, on the other hand, remained faithful to one female vole. So, scientists decided to give extra vasopressin (a hormone found in the prairie vole) receptors to the meadow voles, which have fewer vasopressin receptors.
"The results were remarkable. After the V1a receptor gene was introduced, the former playboys reformed their ways. Suddenly, they fixated on one female, choosing to mate with only her -- even when other females tried to tempt them," reported the BBC News.
The Role of VasopressinSo, what does vasopressin do? And what does it have to do with humans?
The vole escapades interested scientists in researching vasopressin in humans. Although not much is known about its effects, many refer to it as the "monogamy molecule."
In an article entitled, "The Two Become One: The Role of Oxytocin and Vasopressin," Dianne S. Vadney wrote, "Essentially, vasopressin released after intercourse is significant in that it creates a desire in the male to stay with his mate, inspire a protective sense (in humans, perhaps this is what creates almost a jealous tendency) about his mate, and drives him to protect his territory and his offspring. The value of such tendencies toward the maintenance of marriage and family can easily be anticipated."
Economics professor, Jennifer Roback Morse wrote about vasopressin in her book, Smart Sex: Finding Life-Long Love in a Hook-Up World. She says that although men may have a desire to have sex with multiple women, vasopressin helps them to counteract this tendency. She writes, "The man's body tells him that having sex with a woman puts that particular woman into a new and different category. This is not merely an attractive woman: this is a woman who may give birth to his child. She is, therefore, different from other women. The sex act has changed her from a potential sex object to the potential mother of his children, with all that this implies. No matter how sophisticated we think we are, our bodies continue to respond to the sexual act in this way."
Dr. Morse adds that vasopressin causes men to be jealous toward a woman with whom he has been sexually active. It also causes him to be loyal. She gives the example of the vast majority of men who go to great lengths to provide child support for their children, even if they are not permitted to see them. "The view that most men, most of the time, have no attachment to their sex partners is a caricature, a cartoon version of reality. While it may be true that men attach to their sex partners less than women do to theirs, men are not simply looking for a sexual release, but attach to their partners somewhat differently than women attach to theirs," writes Dr. Morse.
What about oxytocin?
Oxytocin is a hormone released in both men and women. Because a response is enhanced by estrogen, women tend to have stronger reactions to oxytocin, which is "thought to be released during hugging, touching and orgasm in both sexes. In the brain, oxytocin is involved in social recognition and bonding, and may be involved in the formation of trust between people and generosity."
So, how does it effect sexual relationships? There are a couple of ways oxytocin affects us in sexual relationships that have ended.
Dr. Eric Keroack said, "Emotional pain causes our bodies to produce an elevated level of endorphins which in turn lowers the level of oxytocin. Therefore, relationship failure leads to pain which leads to elevated endorphins which leads to lower oxytocin the result of which is a lower ability to bond. Many in this increased state of emotional pain and lower oxytocin seek sex as a substitute for love which inevitably leads to another failed relationship, and so, the cycle continues."
Based on the work of Dr. Keroack, we also have this explanation:
"An interesting finding in oxytocin research is the likelihood that oxytocin inhibits the development of tolerance in the brain’s opiate receptors. The excitement of sex is partly credited to endorphins exciting opiate receptors. As a human relationship matures, fewer endorphins are released. If sexual relationships are well bonded, though, the oxytocin response maintains the excitement despite how few endorphins are released. This keeps excitement present between oxytocin-bonded couples.
"In the same way, though, these studies reveal the rationale behind an inability of some to stay bonded in seemingly good relationships. People who have misused sex to become bonded with multiple persons will diminish their oxytocin bonding within their current relationship. In the absence of oxytocin, the person will find less or no excitement. The person will, then, feel the need to move on to what looks more exciting."
Mary Beth Bonacci has a great summary of the normal effects of oxytocin and vasopressin: Oxytocin causes a woman to be forgetful, decreases her ability to think rationally -- and causes an incredibly strong emotional attachment to form with the man she is with. Men also produce some oxytocin during sexual intercourse. But their bodies also produce a hormone called vasopressin. Vasopressin, called "the monogamy molecule," kicks in after sexual activity, and its impact is to heighten a man’s sense of responsibility. It encourages that part of him which says, "My gosh, she may be carrying my child! I’d better get serious about life! I’ve got to get to work, to provide for this family!"