David J. Linden, "The Accidental Mind", Cambridge 2007, is a great read explicating the idea that the brain is not some magnificently designed grand achievement, but an accretion of evolutionary choices. In talking about sexual behaviors and the mind, he offers me the chance to connect the matter of relationships on the individual level into the context of us as migrators.
Linden summarizes, p. 148, with a question:
"So, why have humans evolved such a distinct cluster of sexual behaviors with concealed ovulation, recreational sex, long-term pair bonding, and prolonged paternal involvement?"
By the first, he is referring to the human lack of obvious estrus, so that sex had to become frequent to insure conception. The second behavior follows as a strategy maximizing the chance of conception: sex is so much fun, lets do it a lot. Though not mentioned, this is as true of the female as the male, so that the maximization is carried out by both individuals in coupling; both or either can be libidinous, attracted, and initiate the action. His third item, "long-term pair bonding", is out of place in his question about human evolution, since he is emphasizing biological rather than cultural evolution. The question of the origin of pair-bonding, marriage, can only be solved when we consider the time when males tying women to them became paramount, a recent cultural development. And "paternal involvement" ought to be written "parental involvement", since human child-rearing is one of the functions, not just of one or two individuals, but rather of the mutually supportive group, the social organization we so successfully evolved in. So what is my answer to his question of "why we evolved such sexual behaviors"?
Homo sapiens, having reached a development about 100 millennia ago making them all but superficially identical to us their descendants, was already devoted to a migratory strategy, a creature dependent on gathering and hunting that could be wide-ranging in area and content. Our willingness to move was positive for survival, even if we often moved out of need and not just a sense of adventure. The organizational basis was that of a small group, a band, perhaps, of 20, 40, 60…; lots of blood relations. This organization and strategy were evolutionarily successful, with these ingredients:
the development of language, which is necessarily a group activity;
a rough equality of adult body plan/size/capability;
the possibiity, at any time, of recreational/pleasurable/promiscuous sexual activity and gratification by all individuals, regardless of gender;
this last accompanied by concealed ovulation;
this last perhaps necessitating the development of that chemical-based condition we call "falling/being in love", since that kept the pair together for a few months, increasing the chances for pregnancy (whether the individuals knew it or not);
the always-present possibility of the mother's death in childbirth or after, as well as the general chanciness of longevity even in long-term adulthood for anyone;
the need to support and educate children as they and their brains matured over a multi-year period, a function optimally carried out on a group basis;
the increased margin for band survival and success brought by the involvement by all (maternally or paternally based) in child rearing, protection, education, maturation.
In this traveling band, "long-term pair bonding" (monogamy) would be a factor negative for selection. It would have been a dead end, a death trap, a sure way to decrease the chances for most children to survive. Such children, dependent for years on adults and on the acquisition of language and band mores, would have had a chance only if they existed in a complex of supportive adults, rather than one or two, no matter how devoted. Surely that complex was reinforced by the acquisition and sharing over decades and more of knowledge about the world, travels in it, animals, plants, methodologies related to food, shelter, protection--and more important, its transmission through language and mentorship. I would go further and toss in art, music, dance, story-telling, tool-making, etc, as part of what we developed 50-100 millennia ago (and earlier?); all elements that would reinforce the success of the band, and which the isolation and negatives of pair-bonding would prevent. Even further, or more basic, inefficient brain design (something Linden spends much of his book on) and mutually supportive band organization evolved together as problem and solution, with problem providing strengthening feedback to solution. Another point: if gender identity is in part biological, it would seem that gender identity can be fluid positively just because of the need for band-support where all can have a place, whereas in pair-bond society they not only do not have a place, but might be anathemized.
Paternity, too, would not figure in. Not knowing of his paternity (having bedded several partners over the months) of a child, and having been raised as a contributing member of the band for its survival,and needing the band for his own survival, why would a guy care about paternity? Matrilineality, if important, would be enough for all practical purposes, and as the culture of the band grew more enriched (by itself and by trade and exchange), the special contributions by any member would be more satisfying to him than just being a dad.
Linden suggests that the glow we feel after orgasm is crucial for pair bonding. However, falling in love is chemical, too, an assist to sex (more than once for insurance) and it fades so as not to interfere with maintaining the band. Even more important, maybe is that, evolutionarily, infatuation, being in love, post-coital glow are all temporary states and pass so that there can be many sexual couplings, maximizing diversity. Evolution prefers a series of chemical events around sex that heighten the pleasure, then have it melt deliciously away ready for next time, an activity that keeps everybody around, for sex, for food-collection, for child-rearing. The institution of pair-bonding requires social arrangements to keep the male around regardless of chemistry, just because male-dominated arrangements have replaced the complex of band-support as the primary social institution.
So, to go back to Linden's question, why "long-term pair bonding", monogamy, if it is not in our genes? Because it is in something just as, indeed even more, powerful. Here is the story:
About 15-10 millennia ago, we invented domestication, of plants (wheat, rice), and then of animals. The first led to the need for land and settlement. In both cases, these assets required care in place over time, and somehow, this led to the invention of ownership and property. Could it also have meant a rise of the need to defend your assets? Or did we already have that? In any case, the margin in strength of males now made a difference in determining "mine" and "yours". (Has that margin increased over the past 10 millennia?) Moreover, whether pastoral or agricultural, domestication brought the need for labor to do the work. This could have been done through band-organized labor assignments, but, if it did, that organizing principle did not last, for the result was in fact male dominance, what the feminists call The Patriarchy. Maybe there was a culture war over some centuries. However, getting control of this more dependable, but non-portable, food production method seems a natural lead in to all these inventions: land with boundaries, property, settlement, acquisition, possession, exploitation. The long-term results of greater population with better food security would have been ample justification to argue for, fight for, the change. And once started down that road (to cities, kingship, civilization), rewards would escalate. In any case, standing the earlier mutuality on its head, bonding between a male and (one or more) females did not arise to provide support for the children, but to have ownership (="paternity") over them (as well as the females) in order to ensure a labor supply. Seems painfully marxist.
Now, the point of all this is for today.
All that evolution in our brain and make-up was in support of migratory gathering-hunting bands. And then after tens of millennia it was overlaid in a few millennia by the dense complex of changes brought by the triumph of this cultural revolution of domestication. However, much of the new order's changes run quite contrary to our evolutionary success in the much longer period before 15,000 years ago. Worse, some of the aspects of that success have been subverted and worse -- think about the instinct for band-support and nationalism/patriotism.
However, cultural certainties can be deeply ingrained over a few millennia but still subject to evolution, or in this case re-excavated evolution. The patriarchal organization of human activity leading to civilization backed up by excessive force, "worked" for several millennia, and is still in place for billions of us. But not all. Today, some of us are harking back to genetic heritage and cracking the cultural layers apart; here, anyway. Linden points out genetic change is slow, but he assumes genes favor pair bonding, when for tens of millennia their evolution favored mutual group support. We have been fighting our genes for 10,000 years.
And the erosion of monogamy as a single standard for human relationships is not the only bellwether. The European-Atlantic societies have made great if crab-wise strides away from the bloody excesses of the domestication revolution. Lets hope others can also make similar strides. Certainly, ten or twelve billion of us are not going back to hunting-gathering groups. If some sub-set of us are to blend our genetic inheritance and our civilization to move toward something better, we are going to have to re-think not just our evaluation of monogamy, but the entire range of humanity's socio-political arrangements.