Update: Direct opposition to Sex At Dawn: Humans are more sexually faithful and monogamously minded than many popular depictions want to make us believe. See: "The Myth of the Philandering Man and the Crafty Woman".
Even though sexual utopians can no longer boast (as loudly) about bonobo nonviolence, they often maintain that Bonobo promiscuity would be suitable for humans-presumably because we share a lot of genes and even some behaviors.
However, the sexual utopians are forgetting one thing. Bonobos don't have "pair-bonder brains." We do. Bonobo chimps appear to be our closest living relatives. Zoologists once characterized them as the "make love, not war" hippies of the chimpanzee species, believing them to be non-violent. No longer. (Bonobos not all peace and free love) Like the common chimpanzee, bonobos willingly pursue, kill and eat their primate cousins (monkeys). And unlike common chimps, female bonobos also participate in the mayhem.
Bonobos have a lot in common with us. They sometimes walk upright; they make very human expressions; and they are the only other mammals that ever have sex face-to-face. Bonobos are bisexual, and they rub their genitals on each other a lot. This social glue bonds the troop, and is also useful for making babies, but it does not bond them to individual mates.
Although bonobos may be our closest living genetic relatives, our paths forked more than four million years ago. Our true "closest genetic relatives" were located on our branch even if they're no longer around. Somewhere along that branch humans evolved into pair-bonders.
Experts believe this happened as human skull size increased to a point where babies needed to escape Mom's narrow pelvis in a very undeveloped state. Infants who are helpless and clueless for years enjoy a distinct advantage with two caregivers. A child whose parents bond with each other-at least long enough to bond with that child-more often survive to reproduce. Even today kids with two caregivers do better according to various measures than kids with only one.
Okay, but why should our pair-bonding program cause us to hesitate in partying like our playboy/playgirl bonobo cousins? Because it appears that our ancestors' brains changed in order to shift them from standard mammalian promiscuity to pair bonding. The changes make sex and love with a new partner so thrilling that pair-bonders generally hear rhapsodies, see stars...and want to stick around each other for a while.
Unfortunately, the changes also appear to leave pair-bonder brains more sensitive to seeking highs from addictive substances and activities than the brains of more typical mammals, which don't pair bond. This became evident when scientists offered amphetamines to two vole species. The species are apparently identical but for the fact that one pair bonds and the other is cheerfully promiscuous. Who used more of the drugs and showed higher levels of dopamine in their brains? The pair-bonders. (Dopamine is the neurochemical behind cravings and addictions.)
Non-pair-bonders have more of one type of dopamine receptor called "D1," which seems to play a little-understood role in easing or forestalling cravings for intense stimulation. As pair-bonders, our blueprints also appear to possess extra sensitivity to love and sex. According to neuroendocrinologist Sue Carter, the biochemistry of bonding is likely to be similar in humans and animals because it's quite a basic function. Tellingly, mated humans live longer, and have lower rates of psychological distress, and, significantly, addiction, (Helene Raskin White, Allan V. Horwitz, and Sandra Howell-White, "Becoming Married and Mental Health: A Longitudinal Study of a Cohort of Young Adults," J. of Marriage and the Family, 58(4), 1996: 895-907) than single folk.
For us, teaming up in stable relationships seems to be good medicine (even if we still find novel potential mates alluring thanks to our underlying mammalian heritage). Our bonobo cousins, on the other hand, don't need this pair-bonding medicine at all. To put it another way, we appear to have a little "hole" in our brains. Our brains find pair bonding both enticing and comforting.
When we don't obtain our natural mood medicine in the form of enduring connections with mates, our heightened sensitivity leaves us especially susceptible to seeking substitute "rewarding" stimulation elsewhere. Like the voles offered amphetamines, we seem prone to try drugs, alcohol, Internet porn, casual sex, and so forth, to ease our longings. (More effective ways of finding substitute equilibrium would include friendly interaction, service to others, dancing, support groups, connection with the Divine through prayer or meditation, etc.)
Are we sometimes inadvertently substituting short-term rewards for the deeper sense of satisfaction that actual companionship and regular affectionate touch offer? There's support for the idea that affectionate touch and trusted companionship offer neurochemical benefits that high-dopamine-only activities like cocaine, masturbation, gambling and so forth do not.
The difference may be due in part to levels of "cuddle chemical," that is oxytocin (and its neurochemical cousin, vasopressin). Oxytocin and vasopressin both ease cravings for addictive substances. Oxytocin is also associated with reduced anxiety in males and females. Could this be why sex with intercourse relaxes the nervous system for longer than do-it-yourself sex?
Interestingly, pair-bonding voles have oxytocin and vasopressin receptors in their brain's reward circuitry, which light up when they connect. It's one reason they find bonding so rewarding. When it's not mating season, they seem to enjoy grooming each other, hanging out, and raising their pups together.
While a promiscuous bonobo-like culture might sound like utopia for humans, it may be a luxury that only primates without skull-size/pelvic width issues can afford. Our huge neo-cortex is probably our human consolation prize for those pesky, often subconscious, longings for a pair bond. If we were still non-pair-bonders, we'd probably also still have brains small enough to arrive on the planet more fully developed...so Mom could handle the job of raising us herself. Pair bonding, romance, and brains more sensitive to addictive substances and activities, seem to be the price for our huge skulls. Tell that to those bonobo party animals.
And the next time someone informs you that we humans would be better off as promiscuous as our distant bonobo relatives, tell them you doubt we have the brain design for it. A bonobo lifestyle just won't completely do it for us pair-bonders no matter how many orgasms (or other short-term highs) we engineer. We'll always feel like something is missing, even if we can't consciously put our finger on exactly what it is, and even if a beer sometimes looks like a good substitute.
This fossil find suggests that our pair-bonding ancestors may go back even farther than we thought. Did Early Humans Start Walking for Sex? http://blogs.ngm.com/blog_central/2009/10/did-early-humans-start-walking...
UPDATE (2018) Contrary to the cliché of "satyr apes", bonobos spend twice as much time on playing as on sex. Study: Time choices: the 'sexy ape' spends far more time in play than in sex