Sunday, January 19, 2014

Lust, Romance, and Pair Bonding

You’ve now had a chance to read about four of the couples I interviewed.  I chose these couples to profile because they represent the range of differences I encountered fairly well.  (There was one obvious exception:  because I was also favoring the more reflective and articulate interviews, the couples I ended up choosing to describe for you were all college educated, and four of the eight individuals have at least a masters, whereas seven of the people I interviewed had some or no college.)

But as you read through this series of posts, you should have noticed a clear similarity:  all four of these couples are strongly devoted to each other.  In this, they are completely representative of all of the (now almost 60) couples I've interviewed.  To understand why, we need to take a step back and look at why this question even comes up.  Why aren’t humans, like many species, simply hardwired to be either monogamous or promiscuous?

Humans: A Thoroughly Mixed Up Species

Human evolution contains a lot of puzzles, but few are as complicated and fascinating as the questions about human mating and sexual behavior.  For example, most primates and many other birds and mammals can be classified as either “tournament” species or “pair-bonding” species, based on their mating patterns and other characteristics.  Many variations and exceptions do occur, but…

In a typical tournament species:

  • Males compete for top status, usually by displays, threats, or physical combat.
  • Males are larger and stronger than females.  (Think of a bull walrus or elk.)  In many species, the average male is more than twice as large as the average female, and the smallest male is larger than the largest female.
  • Males often have other secondary sexual characteristics for combat or display, such as fangs, tusks, antlers, bright colors, or peacock tails.
  • The top-ranking males father nearly all of the offspring (e.g., 5% of males fathering 95% of the offspring).
  • Copulation occurs in public and is of little or no interest to others.
  • Males guard females, but females exhibit no signs of sexual jealousy.
  • Females usually have only one offspring at a time.
  • Males contribute little or nothing to feeding or rearing their offspring.
  • Females are able to feed and rear their offspring without help from the fathers.
  • Offspring stay with their mothers until they can care for themselves.
  • Infanticide is common, as new alpha males kill rivals’ offspring so they can get the females pregnant sooner.

In a typical pair-bond species:

  • Males are chosen by females based on indicators of loyalty, fitness, and parenting skills.
  • Males and females are the same size and may be hard to tell apart.
  • Most males who mate at all have nearly the same number of offspring (e.g., 95% of the adult males fathering 100% of the offspring).
  • Copulation often takes place in private.
  • Either or both genders may practice mate guarding and exhibit sexual jealousy.
  • A female often or always has multiple offspring.
  • Fathers contribute at least as much as mothers to feeding and rearing their offspring, and often contribute more.
  • A female usually cannot feed and rear even one child without help from the father. (Usually because the eggs/infants must be guarded or protected while the other parent finds food.)
  • Offspring stay with their fathers until they can care for themselves, but mothers may abandon their mates and offspring to go off and start another family when their children are old enough to survive with just the father’s care.
  • Infanticide is rare.
So what are humans?  We’re weird, that’s what.  We’re in between on almost all of these things!

For example:

  • Some human cultures resemble tournament species.  Think of any sultan with his harem and too many royal offspring to count.  Or think of the Middle Ages, when a local baron and his sons and brothers could potentially father half of the local babies.   On the other hand, there are many human cultures (like the US before 1960) that look much more like pair-bonding societies, where monogamy is the norm, no matter how often that norm is breached.
  • Among humans, males are slightly larger than females, but much less so than in most tournament species.  Among our ancestors millions of years ago, males were much larger than females.  We have been evolving away from that in the direction of height equality.
  • Among humans, males and females BOTH have strong secondary sexual characteristics.
  • Copulation usually takes place in private, but humans are the only mammals to be obsessively interested in and aroused by the sight or sound of others having sex.
  • Both genders practice mate guarding and exhibit sexual jealousy.
  • Human children are more helpless for far longer than those of any other species, so mothers need more help for a longer period, but males may or may not help rear their young. Fathers are the obvious choice as helpers, so long infant dependency should mean that humans would be an extreme pair-bonding species, but we aren’t.
  • Human infants are more likely to be killed by their mother’s new boyfriend or husband than by anyone else, but infanticide is still relatively rare.
The point about secondary sexual displays is especially strange.  Secondary sexual characteristics evolve in one gender only when the other gender is doing the mate selection.  We take it for granted that men and women alike are both selecting for attractive mates, but when you look at other species, this just doesn’t happen.  It’s almost always one gender or the other doing the choosing, not both, and the drab, inconspicuous gender is the one with all the power.  It’s the dowdy peahens who created the peacock’s finery by selecting the males with the showiest tails.

In the case of humans, both the female breast and the male penis have been enlarged by sexual selection to a degree that seems absurdly nonfunctional.  The chimp penis looks like a skinny pink three-inch nail. The gorilla penis is even stubbier, only an inch and a half long! Compared with them, the human penis is gargantuan, 10 to 20 times the volume when erect.  And out of roughly 4,000 mammal species, only human females have prominent breasts when not lactating.  Which argues that for at least one long period of time in our evolution, both men and women – or proto-human males and females – were heavily selecting mates for appearance.

Brains + Culture = Plasticity of Behavior

The evolutionary “problem” that humans face is that in some ways we’re too smart and flexible for our own good.  The mother of a small child whose father is dead or absent can usually find others – another male, her parents, her siblings, and the extended family, clan, tribe, or village – to help her.  The reality is that in many hunter/gatherer societies, a woman with a baby was fairly self-sufficient.  Women in such societies often shared childcare, nursing, and food gathering activities communally.  They needed the men – acting together – to defend against enemies and predators and to provide meat, which again was usually shared communally.

Infanticide by violence or neglect remained a big risk for the fatherless child, and a woman could certainly benefit from attracting a strong, smart, high status man and getting him to help raise, protect, teach, and sponsor her kids.  But a high status male has lots of choices and is less likely to hang around helping with the kids, so she could also gain almost as much, or even more, from attracting a mid-status average guy who was devoted to her and her children.

Cryptic Ovulation

Mathematically, there's an ever better alternative from an evolutionary point of view, if she can pull it off: keep the regular guy devoted to her and her children, but sneak off into the bushes with the high status male when she is fertile and get his genes for her kids.

But this doesn’t work very well if her lower-status consort can tell when she’s fertile, since he can then try to guard her 24 hours a day for those few days.  So if that’s her plan, it helps a great deal if she can be sexually receptive year round and not give off any clues about when she’s ovulating.  The fact that we evolved very strongly in this direction suggests that our distant ancestors went through at least one long period in which this sort of ability to hide ovulation from men was important to human reproductive success.  And it’s important to note that this is not something that would evolve in a truly monogamous species!

How did the males respond to this evolution of concealed ovulation?  Even though the proto-human (or early human) male couldn’t tell when a female was fertile, he was still likely to stick around because a) he got lots of sex, b) she might not have an opportunity to cheat on him on one of the days when she’s fertile, and c) even if she did sneak around on him, he still had a good chance of being the father if he mated with her often during her fertile period.  Furthermore, since he didn’t know when that would be, it was in his interest to have sex with her as often as possible (which naturally cut down on his opportunities to sneak off with some bimbo from across the river).

Of course, that situation also gave men a reason to want to guard and protect their women against other men.  Since males in a nomadic tribe depend on each other for mutual support in hunting, fighting, and territorial defense, they have powerful reasons not to antagonize each other, so they have an incentive to come up with cooperative rules that reinforce monogamy.  The obvious deal was, basically, ‘you don’t sneak off into the bushes with my mate and I won’t sneak off with yours, and together we’ll chase away any strange males who come sniffing around any of them.’  Again, this is a familiar pattern from many human societies.

On the other hand, the males have no reproductive reason not to take any sexual opportunities that come along.  Given the chance to act like a tournament "alpha" male, making many babies with many women and caring for none of them, in the hopes that some of them will make it, or of keeping one woman positively pregnant by him, and helping raise her kids and giving them a big advantage over other guys’ random bastards, evolutionary logic says that the human male should stoutly proclaim, “I want to do BOTH!”

And, in fact, the best evolutionary strategy for males is to do both … if they can get away with it.  But that immediately comes up against the hard fact that if some males succeed at the tournament strategy, all the other males lose, so it is now in the interest of those other males to gang up on and kill, maim, banish, or otherwise stop the would-be successful alphas.

Nomadic bands, like the ones humans inhabited through most of the time we were evolving, are typically small groups that are tight-knit and extremely averse to any kind of internal conflict, so this sort of behavior would have been rare within the band.  But agriculture led to large settlements, armies, and hierarchies of power that allowed "alpha" behavior to flourish for some powerful individuals in spite of its tendency to create conflict.

Of course, such conflict over mates can be wasteful and disruptive, often leading to violent clashes, feuds, and even wars.  (The Iliad is the classic example.)  As societies became more established, religion and the state took over more of the enforcement responsibility in order to minimize this violence.  Depending on the society and religion, this led to things like publicly registered and sanctioned marriages, child-support laws, paternity suits, and laws against adultery, bigamy, polygamy, rape, and statutory rape, as well as to religious hostility toward all sex outside of marriage.

Genes, Culture, and Mating Patterns

All of this sets up a lot of tricky cross-currents and possibilities for cultural rules to go one way or another.  And that’s where things really get crazy.  Humans have brains and language, which means we come up with abstract ideas and novel rules of behavior, which means that we are constantly trying out those ideas to see where they lead, which means that just about every possible cultural arrangement has been tried at one time or another.  We’re also extraordinarily adaptable.  Where other species have strong instincts, we have mild inclinations.  If culture and circumstances require us to ignore those inclinations, we do.  It may make us less happy, but if it works, it works.

As a result, we have official monogamy in some societies and harems and optional polygamy in others.  We get women in burkas, covered from head to toe in shapeless black, genitally mutilated so they can’t enjoy sex, sold from father to husband for a bride price, and never allowed to drive or go out in public without a close male relative.  And we also get women wearing bikinis or nothing at all, strolling unmolested on public beaches, women who are able to pick – and leave – their male partners without anyone’s permission. We get cultures in which men own women, and we get cultures that insist that women own their own bodies and that “No means NO.”

Because there is so much variation, anthropologists have learned to be cautious about generalizing about sex.  However, there are a few things we can say with confidence:
  • In every society we know about, most people fall in love and pair off as couples that last for years, decades, or a lifetime.
  • "Social monogamy" - having one official spouse - is not the same thing as 100% sexual monogamy.
  • Most human societies on record explicitly allow for polygamous marriage.
  • Even in polygamous societies, most people have only one spouse at a time.
  • Even monogamous cultures generally allow for some wealthy and powerful men to raise multiple families by a wife and one or more mistresses.

In other words, studying human evolution and cultural diversity does not let us say that any arrangement, from monogamy to polygyny to "polyamory" to complete promiscuity is "natural" or "unnatural."  As Dr. Emily Nogaski put it in the dirty normal:
Human sexuality is not designed to function in open relationships any more than it is designed to function in socially and reproductively monogamous relationships. What human sexuality is DESIGNED to be is massively variable, plastic, adaptable, and diverse. ALL of it is “natural” – and that’s all evolution can tell us. The sociosexual environment in which we evolved is no easier or more comfortable or “natural” than any other; there is no system that is easy and comfortable for everyone; all sociosexual systems involve rules about what is or is not okay, and those rules will feel oppressive and wrong to SOMEONE.
There are many practical arguments to be made for some form of monogamy.  For example, there is some evidence that monogamous societies tend to be more egalitarian and less violent, and a great deal of evidence that monogamy is the best system for raising healthy and successful children.  But the argument that monogamy is "natural" is clearly wrong.  If it were, our "nature" and our culture would be aligned with each other at all times and it would not be such a struggle for many people in monogamous societies to pair off and stay together.

One of the results of our mixed up evolution and our extraordinary social and cultural adaptability is that we are a mass of conflicting impulses and contradictory answers to basic evolutionary problems.  And a large part of the problem is that our evolution has left us with no less than three overlapping mating systems as a result:


If there’s a chance for sex with an attractive member of the opposite sex, and the risks seem tolerable, this part of the brain says, go for it!  This response is fast, opportunistic, and driven by testosterone and adrenaline in both genders, but it is also highly inhibited by circumstances, especially for women.

This system is the oldest subsystem, designed for the most primitive evolutionary strategy: whenever you get the chance, reproduce.  In most people, it gets overruled by the forebrain at least 99.9% of the time, but it often figures in our fantasies and dreams, where there are no adverse consequences to inhibit it.


Ah, love!  Picking the best genes to partner with!  Novelty, competition, excitement, dopamine!  Romance tends to be all or nothing. It is normally inhibited by the high opportunity cost (do I fall for this person or wait for someone better?) until a good choice comes along, but when people do fall for each other, they tend to fall hard, behaving in a variety of obsessive ways.  (Serotonin, usually thought of as a feel-good chemical, actually falls during intense romantic episodes, and low serotonin is one of the triggers for obsessive/compulsive behavior.)

Being head over heels in love is not all joy.  At some level, we know that our obsession with our loved one is making us do irrational things, but we just don’t care.  In addition, dopamine, which is triggered by novelty and the unexpected, also acts as an amplifier of emotions, both good and bad, so high dopamine can send you both up and down, depending on the situation.  (Lovers’ mood swings, anyone?)  Romantic love can last anywhere from a few weeks to a few years for most couples.

Pair-bonding/long-term love

This is the system that keeps couples together for the long haul. It evolved to a large extent from systems that originally facilitated parent-child bonding.  Oxytocin and vasopressin are the key neurotransmitters here, and they are generated in the brain by – and help reinforce – physical contact, pleasure, safety, caring, love, trust, and loyalty.  The biology of the pair-bonding systems in our brains is old, but it’s likely that we humans are descended from ancestors who were a tournament species, and we only started to evolve toward the pair-bonding end of the spectrum in the last few million years, or even the last few hundred thousand years.  Clearly we aren’t all the way there.

Conflicting Impulses

To complicate things further, humans are spread across many different environments, each with their own ecologies and physical challenges, from the cold of the Arctic to the hottest deserts and the wettest jungles.  Each of these environments creates different problems for culture to solve, requiring enormous flexibility as humans move into new regions.  And because human cultures can be even more variable than human environments, we have evolved most of all for an ability to learn the rules of our own culture and to find ways to be successful within those rules.

What this means is that we all have the capability to behave, more or less, like members of a pair-bonding species, or a tournament species, or some mixed up hybrid of the two. Those of us who have genes that incline us toward strong bonding and who experienced strong examples and cultural conditioning toward wanting to be part of a loving long-term relationship have the ability to do that.  But not everyone can do so easily, nor does everyone want to.

One of the problems therapists see when couples come in for counseling is that one or both of the members of the couple are stuck with an image of sexuality and arousal that depends on one of the first two systems.  They want the raw lust of sex with a stranger or the intense roller coaster thrill of being in love, and that’s just not there with old Ms. or Mr. Familiar.

A lot of therapists and would-be experts respond by telling people how to put the “thrill” back in their marriages by experimenting constantly with new things:  do a striptease for your partner, appear at the door wrapped only in Saran Wrap, watch porn together, role-play rape fantasies, experiment with S&M or bondage or open marriage, or whatever.  But the perpetual quest for novelty and excitement almost inevitably runs a couple into dangerous ground after a while.  They eventually run out of new options and become jaded with the old ones, and they find that they are objectifying each other more and more and actually becoming more remote from each other.

The real problem, I think, is that there are very different styles of sex appropriate to each of the three attraction systems, and people who want to be in satisfying long-term relationships don’t always make the transition to the kind of sex that can sustain that kind of relationship.  We’ll look into this question in detail in the next post!

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