I like to think of myself as courageously seeking out important truths, however uncomfortable. But like most would-be-courageous folk, I don’t really know what I want until I get it. I was excited to read the contrarian Sex at Dawn, which suggests sexual promiscuity is our forager heritage. But that pretty sparkler was really a grenade – its uncomfortable truths shook me to my core.
To hear a different view, immediately afterward I read Evolutionary Biology of Human Female Sexuality [EBoHFS], which supports a standard view of foragers as long-term pair-bonders. By comparison, EBoHFS is more academic: dry, clinical, verbose, and careful to define terms and consider many possibilities. It reviews an immense number of studies, and appears to takes a cautious middle ground.
Sex at Dawn, in contrast, frustrates academic sensibilities. It is passionate, partisan, even snide. It doesn’t systematically review evidence pro and con, or points of view, and it takes long detours to settle scores with opponents. It is long on anecdotes and examples, relative to systematic data. Its authors are confused on how economists use “selfishness”, and on basic Malthusian population theory; they aren’t really to be trusted on theory. Furthermore, their relationship advice seems flippant.
But on their key claim, that forager females were sexually promiscuous, I am persuaded: they are basically right. EBoHFS hardly offers any contrary evidence, it just keeps repeating that evidence is ambiguous, while embracing the usual story by default. (Sex at Dawn also gets forager peacefulness right – see Chapter 13.) Searching for expert critical reviews, the closest I found were this and this, which mainly just complain it is all very complex and no simple generalizations apply.
The basic facts are these. Recent humans mostly had long-term pair-bonds, while our two closest primate relatives, chimps and bonobos, are quite sexually promiscuous. Yes, they hardly mate at random, and may return often to favorites. Even so:
“Among chimpanzees, ovulating females mate, on average, from six to eight times per day, and they are often eager to respond to the mating invitations of any and all males in the group. … A recent study … showed that more than half the young (seven of thirteen) had been fathered by males from outside the female’s home group.” [p70]
Bonobos females are even more promiscuous. In fact, to find biological analogues to recent human monogamy, EBoHFS looks to various kinds of birds; mammals won’t do. “Monogamy is not found in any social, group-living primate.” [p64]
The big question then is when did the biologically-rare (3% of mammals) phenomena of (near) monogamy arise in our lineage, millions of years ago with the rise of humans, or ten thousand years ago with the rise of farming? And since our data on modern foragers suggests that farming at least greatly reduced promiscuity (especially for females), the big question is really whether lightning struck once or twice, i.e., if there were one or two big unprecedented moves away from typical social-primate promiscuity. Occam’s razor suggests one lightning strike.
If human sex were like chimp and bonobo sex, how should we expect it adapt to human changes, like larger brains, group sizes, and lifespans, and more egalitarian sharing? Dunbar says brain size, group size, and grooming time fraction correlate, and says language let humans better “groom” our record size groups. If sex was part of “grooming”, we’d expect humans to spend a record fraction of time on sex. We should also expect more adaptations to longer term relations (like pedophilia).
So what is the data? Humans spend more time having sex than any known species. Human sex shares many otherwise-rare features with the promiscuous bonobos, who hide their fertile days and have sex all month long, in many positions including missionary where they gaze into each other’s eyes and kiss deeply. Bonobos share food with sex, and use sex for social bonding, such as via homosexuality. Human sex has many other features understandable as adaptations to promiscuity, including large external testicles, a record size penis designed to scoop away other semen, men preferring high male-to-female ratios in porn, long frequent sex, and women being louder and lasting longer than men.
Monogamy vs. promiscuity is a rare area where academics and cultural elites tend to favor the conservative/farmer side of the forager vs. farmer divide. While I find myself balking at the idea of embracing sex partners with forager promiscuity levels, I accept that this preference was culturally imprinted on me.
Many Sex At Dawn quotes below the fold: Continue reading "Sex At Dawn Is Right" »
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