What makes a person homosexual is a mystery still to be revealed — as well as a sociopolitical hot potato. But let's talk about what the oxytocin hypothesis might mean for same-sex relationships.
Certainly, gay men and lesbian women love and bond the same way that straight people do. Their hypothalami produce the same spurts of oxytocin and vasopressin, and they enjoy the same exciting rushes of dopamine. Sex creates the same association in the brain's reward system between a sex partner and feeling great, inscribing a social memory that causes one person to prefer another.
In gay love, however, limbic resonance — that condition in which two people's physiological states become attuned — may be, well, more resonant, because the lovers' systems are more alike than those of a heterosexual pair.
There's an old joke in the gay community: What does a lesbian bring on the second date? A U-Haul. What does a gay man bring? A friend. There's some neurochemical truth to this joke. When two women have sex, the oxytocin surge can induce cuddling that lasts for days. Two male lovers, under the heavier influence of vasopressin, to say nothing of testosterone, may quickly feel ready to move on physically and emotionally after lovemaking.
In addition to the match in brain chemistry in same-sex couples, there's evidence that one partner — gay or straight — can absorb the other's sex and bonding chemicals; in a same-sex couple, this could heap on an extra helping of estrogen or testosterone. Estrogen and testosterone may be exchanged via lovers' sweat and saliva. How do one person's sex steroids get into the other person's brain? Most mammals have a special area in the nose called the vomeronasal organ. This sensitive tissue, located in the nasal passages, sends molecules inhaled by the animal directly to the brain, where they can influence behavior. This organ reacts to pheromones, the chemical-signaling substances put out by many animals, from insects to apes. It's the organ that draws a female elephant to the temporin secreted by a bull in his prime.
Human fetuses have a vomeronasal organ, and for a long time, biologists thought that it was a vestigial structure that disappeared by birth. But recently, researchers have found evidence that the human response to pheromones is alive and well in adults.
If people of all sexual flavors react to the neurochemicals they swap when they canoodle, in a gay couple, this may reinforce their neurochemical states. Remember, estrogen increases the effects of oxytocin, while testosterone decreases them. So, with every nuzzle, taste, and touch, a same-sex pair creates a neurochemical feedback loop that reinforces the tendencies of their sex.
When two women engage in intimate behavior, from hanging out with a friend to wild lovemaking, it's likely that, with every breath, each takes in molecules of estrogen and oxytocin emitted by the other's body. Two men enjoying the same behaviors likely inhale each other's testosterone, oxytocin, and vasopressin. Overall, two women may experience more oxytocin in their relationship than a man and a woman, and two men may experience less oxytocin and more vasopressin.
It's crucial to note here that all men and women — gay, straight, and in between — possess a wide range of temperaments and tendencies. Men gay and straight may find it extremely easy to bond, while women of all sexual persuasions run the gamut from runaround to stay-at-home. The important thing is that for all of us, gay and straight, the neurochemistry of bonding is the same.