Following a number of conversations and even throwaway remarks from various people lately that have got me wondering, I decided to investigate the extent to which our typical relationship patterns (such as monogamous marriage) can be considered “natural”, and I came across this brilliant article by David Brin.
The bulk of the article provides the groundwork for some speculative statements on the evolutionary origins of various physiological characteristics of women – which are interesting, and slightly disturbing in places – but it was this groundwork that provided some answers to my question, which I will summarise here.
There is a correlation between harem size – that is, “the number of ‘wives’ a prime male in a species impregnates during his lifetime” – and the ratio of male to female body size (bigger harems mean more competition between males, which drives an increase in their physical size). However, even in monogamous species (such as birds), where the harem size and body size ratio are both 1, males will occasionally engage in “opportunistic philandering” where this poses a low risk to them and their family. So monogamy is more a matter of devotion than strict fidelity.
I’ll just let the shock of that settle in for a moment, yes? 😯
The human body size ratio predicts a harem size for humans of about 1.1-1.4. This means monogamy does make sense for humans; however, “human males show an incredible range of motivation and behavior” stemming from a complex evolutionary history. The problem for women, of course, is that human infants require a lot of nurturing, and this fact results in competition between women for the men who are motivated to be fathers (beyond the act of conception ;)).
So, in the history of our species, men have had to compete for women (because polygamy is possible, therefore some men could miss out); but women have also had to compete for men (because there is a shortage of “good” ones from their point of view).
Not that this was any surprise to me by this point, Brin concludes that “there is no design possible for a human utopia. Whatever society we put together will at best be a network of compromises.”
The mechanisms for the inclination towards pair-bonding (falling in love, being faithful) have to do with receptors in the brain for hormones such as oxytocin and vasopressin. As I learnt from this talk a few months ago, this type of evolved mechanism is what makes us care for one another and, along with empathy, this compassion is the biological root of our sense of morality. The variation in human male relationship preferences, I gather, may be mirrored by variation in this brain chemistry.
But on the other hand, behaviour is heavily conditioned by environment (e.g. resources) and culture. This is where it gets more positive. I’m increasingly convinced that we are not only behaviourally flexible but are well-equipped, with our intelligence and compassion, to be morally creative and invent harm-reducing ways of living that go beyond the various instincts evolution has dumped us with.
Facing the truth about our natures, and de-stigmatising our less socially-acceptable motivations for a more frank treatment of them, can only help us find the best compromises and embrace them willingly.
As Brin says beautifully at the end:
“Once people of good will, both men and women, are better aware of the hand dealt them by evolution, they must almost certainly grow better at playing it.”
“For all its tragic implications, this cycle of mutual selection has meant that both genders experience much the same range of emotions during their lifetimes. True, men and women seem at times to concentrate on different priorities, which come into sad conflict in our present culture. But standing back, one can say without any doubt that both girls and boys grow up knowing what it’s like to feel the fear and excitement of initiating an encounter, as well as being the one to evaluate or choose, to accept or refuse. In most species these activities are strictly reserved for one sex or the other, but men and women both experience rejection, and each knows all the happy and aggravating phases of bonding. This may help women and men empathize with each other to a degree I would suspect is unprecedented between the sexes in nature, where males and females have little experience of each others’ ways. Those who perceive only the gulf between men and women should take note.
Finally, although we may have stumbled about blindly in our million years of feverish adaptation, and while we now find ourselves boxed in, with little hope for anything like utopia, there is no cause for shame. If we are awkward and uneven in our adaptations, it is because we are a people still in rapid flux. One cannot hope or expect that a species will be perfectly at peace with itself when it is still in furious transition from what it once was, toward what it eventually may become. The first species ever to have some control or choice about that destiny.
Compassion is the trait we may be most proud of. Ironically, it can have come from nowhere else than the bizarre story of our ancestors’ competition for reproductive success.”