In terms of its outcome, the wedding ceremony can be seen as a glass half empty or a glass half full, an interpretation that no doubt is shaped by our own experiences with the person we enjoyed that day with. In terms of its function, there is no doubt about the interpretation of why we go to such lengths in the wedding ceremony: It is a ritualized solution to the commitment problem. The wedding ceremony is our attempt as a culture to get two young partners to remain faithful to one another (and devoted to their offspring) in the face of so many compelling alternatives; to sacrifice their pursuit of sexual desire to the interests of their bond and their offspring. Culture’s answer is to empty the bank account, bring every person you cherish into a sublimely beautiful locale, make public avowals, give expensive rings to one another, photograph every instant of the day in the event that memory fades, and head off into the sunset. Evolution’s answer to the commitment problem is that emotion most favored by poets and rock stars alike: romantic love.
Romantic love enables the human mind to countervail self-interest. In the depths of romantic love, we idealize our partners; they take on unique, mythic qualities; we turn to deistic metaphors to describe our beloved. When Sandra Murray and her colleagues asked romantic partners to rate themselves and their partners in terms of different virtues (understanding, patient), positive traits (humorous, playful) and faults (plaintive, distant), they found that happier couples idealized their partners; they overestimated their partners’ virtues (compared to the partners’ self-descriptions) and underestimated their faults. In other studies, Murray and colleagues asked people to write about their partners’ greatest fault—the source of endless vitriol in therapy sessions and divorce proceedings. Happier romantic partners were more likely to see virtues in faults and more likely to offer “yes, but” refutations of faults. A happier married wife would look at her lethargic husband on the couch, snoozing with the remote pressed into his cheek, and think, “yeah, but at least he is around more in the home and not cavorting at the sports bar or at the golf course all day Saturday.”
Studies point to a neurological basis for romantic love’s rose-colored glasses. Not too surprisingly, long-term committed romantic love is associated with activation in reward centers in the brain—the ventral anterior cingulate, the medial insula, the caudate and the putamen. More dramatically, romantic love deactivates threat detection regions of the brain—the right prefrontal cortical regions and the amygdala. The person in the throes of romantic love may be physiologically incapable of seeing all that is worrisome, problematic, or worthy of a skeptical second look.
And studies have begun to document the very chemical that promotes long-term devotion. We can pin our hopes on oxytocin, a mammalian hormone, or neuropeptide, consisting of nine amino acids, and involved in humans, as any midwife will tell you, in uterine contractions, milk letdown, and breastfeeding. Oxytocin is produced in the hypothalamus, an old region of the brain that coordinates basic behaviors related to food intake, reproduction, defense, and attack. It is then released into both brain and bloodstream, which is why it is called a neuropeptide. Receptors in the olfactory system, neural pathways associated with touch, and regions of the spinal cord that regulate the autonomic nervous system, especially the parasympathetic branch, including the vagus nerve (see chapter 11), await the chemical’s arrival.
By activating touch and a calmer physiological state, oxytocin enables monogamous pair-bonding. This remarkable discovery emerged in Sue Carter and Tom Insel’s comparisons of two nearly genetically identical rodents, the monogamous prairie vole and the promiscuous montane vole. The most notable neurological difference between the two species is the density and distribution of oxytocin receptors in their brains, the monogamous prairie vole enjoying greater densities of oxytocin receptors. Moreover, injections of oxytocin into appropriate brain areas lead the montane vole to preferences for a single partner over other partners, while injections of oxytocin blockers render the prairie vole less capable of monogamy. Other studies of voles find that oxytocin increases after sexual behavior, and that injections of oxytocin increase social contact and pro-social behavior, whereas blocking the activity of oxytocin prevents maternal behavior.
Studies of other species yield similar results. In primates, injections of oxytocin increase touching behavior and gaze focused on infants, and decrease threatening facial displays such as teeth-baring yawns. Little domestic chicks, when separated from their mother, emit fewer separation distress calls after they have been given a dose of oxytocin. Oxytocin injections cause ewes to become attached to unfamiliar lambs.
Right now I suspect you’re asking three questions. What about humans, that most complex of the pair-bonding species? Isn’t oxytocin what Rush Limbaugh was addicted to? (No, that was OxyContin, an opioid painkiller; one wonders what his show would’ve been like had he grown addicted to oxytocin.) And where can I get this oxytocin and sprinkle it on my partner’s morning Corn Flakes?
With respect to the first question, the literature on oxytocin in humans is beginning to reveal an equally compelling picture of the physiological underpinnings of love, devotion, and trust. In studies of lactating women, it has been found that oxytocin reduces activity of the hypothalamic-pituitary-adrenal axis, the physiological basis of stress. Prepartum mothers who show higher baseline levels of oxytocin later show increased attachment-related behavior with their new babies. Oxytocin is released in response to pleasurable massage and sex. Even chocolate triggers oxytocin release. It’s not a coincidence that we give chocolate to loved ones on Valentine’s Day, and not pickles, Pringles, or salsa—we’re seeking to stimulate that feeling of trust and devotion.
So what about romantic love? To more directly document the relationship between oxytocin and romantic love, Gian Gonzaga and I undertook a Darwinian study of sexual desire and romantic love. Gian first did what a good descendant of Darwin does: He turned to Darwin’s own observations. Darwin identified three kinds of love—“maternal love,” “love,” and “romantic love” (see table below)—which closely parallel our designations of caretaker love, romantic love, and desire, although Darwin uses the term “romantic love” to refer to what we now call sexual desire.
DARWIN’S DESCRIPTIONS OF THE VARIETIES OF LOVE
MATERNAL LOVE
TOUCH, GENTLE SMILE, TENDER EYES
LOVE
BEAMING EYES, SMILING CHEEKS (WHEN SEEING OLD FRIEND), TOUCH, GENTLE SMILE, PROTRUDING LIPS (IN CHIMPS), KISSING, NOSE RUBS
ROMANTIC LOVE
BREATHING HURRIED, FACES FLUSHED
Then Gian, envy of his graduate-student peers, sequestered himself in the depths of the library stacks and surveyed dozens of not-so-lurid studies of the nonverbal displays that accompany sexual intercourse versus friendly, affectionate contact in humans and nonhuman primates. What he identified were possible display behaviors that signal sexual desire and romantic love. Prior to sex, human and nonhuman primates tend to engage in a variety of lip-and mouth-related behaviors—they pucker lips, kiss, lick their lips, and stick their tongue out, stock in trade for rock and rollers like Mick Jagger.