The paleo diet is primarily about applying evolutionary principles to nutrition. But nutrition is certainly not the only subject evolutionary science can lend its wisdom to. Long before I had heard of the paleo diet, I had a keen interest in the controversial science of evolutionary psychology. In high school, Steven Pinker’s The Blank Slate fueled plenty of arguments with my family and in classes.
Here is another evolutionary psychology book that seems to be designed to start arguments, since it’s about something nearly everyone seems to have an opinion about. Sex at Dawn, written by psychologist Christopher Ryan and psychiatrist Cacilda Jethá, is snarky and perhaps intentionally provocative, but no matter your opinion, it will probably make you rethink some long-held assumptions about sex.
I come from a culture where growing up, I was preached that the ideal was that you would only have sex with one person and they would only have sex with you. As an adolescent I was assaulted with books extolling the evils of animal-like promiscuity. Surely it caused ye to be dishonored and blighted with syphilis and live destitute with 14 children in a trailer. Having one true love was ordained by God and temptations otherwise were certainly of the Devil. It’s kind of a miracle that I’ve been able to move on and have normal relationships, but intrinsic human desire tends to win out when confronted with freedom.
It doesn’t take a genius to figure out that humans have a tough time following such a doctrine. A pastor in my own church growing up was one of those who struggled and his divorce almost broke up the congregation.
It’s no wonder we have such a tough time— evolutionary speaking, we are a hypersexual species with marked physical adaptations for promiscuity. Sex at Dawn presents some interesting evidence for this, as well as a romp through human history. Paleo dieters will be familiar with the idea that hunter-gatherers were healthy and happy, which gets several chapters here. I did learn one new fact, which is that one of the techniques used to estimate age of bones, dental eruption, only says that the person was over 35, but some idiotic studies have underestimated lifespan because they took these studies and recorded 35 as the age of death.
But back to sex, since that’s probably what you were thinking about anyway. There has certainly been ample speculation about Paleolithic sex, with the general narrative being that women have always sought to procure a stable man to help with children and bring home wooly mammoth kabobs, while hooking up with the hot jerk on the side. Meanwhile men have always just tried to knock up as many women as possible while trying valiantly to only provide meat to their own offspring. Jethá and Ryan dismantle this frankly stupid just-so story well. It just doesn’t make sense in light of anatomy or how hunter-gatherers actually live. It requires that every culture be organized around marriage, fathers provide mainly for their own children, that sex is connected to paternity and that men are somehow able to discern paternity, and that hunters could refuse to share their meat with others. In reality, while sex habits seem to vary, hunter-gatherers almost always share meat (and raise children) communally and several cultures do not even recognize paternity in the modern sense of the word.
Unfortunately, numerous evolutionary scientists have operated under this errant view and it remains fairly mainstream.
So where is the evidence otherwise? The authors look at comparative anatomy with other apes. Our closest true-monogamous relatives are gibbons, which share very little in common with humans otherwise. Our closest living relatives are bonobos, who are hypersexual and promiscuous, but as I’ve pointed out in nutritional anthropology posts, they aren’t that close (though it’s interesting that even they hunt for and prize meat). One interesting thing we have in common with bonobos is a repetitive microsatellite important to the release of oxytocin, which is absent in chimps and important for pro-social feelings like love and eroticism. Bonobos also share the unusual habit of copulating throughout the menstrual cycle, lactation, and pregnancy. Like us, their vulva is oriented towards the front of the body, rather than the rear as in chimps.
Next the authors examine studied hunter-gatherers. There are certainly no tribes practicing the ideal of one lifetime sexual partner. In face, most seem to enjoy lots of sex with many people— “Anthropologist Thomas Gregor reported eighty-right ongoing affairs among the thirty-seven adults in the Mehinaku village he studied in Brazil.” They also take down the ideal of the “nuclear family”- which no hunter-gatherer culture practices either. In tribal cultures the extended family (which is often the entire village) is where children are raised.
But as post-agrarian hunter-gatherers are an imperfect reflection of the Stone Age, so the anatomy information is even more interesting. In terms of several important anatomical markers, humans show evidence that we engage primarily in sperm competition, which has huge implications. Some men I know seem to think men evolved to be promicious, but women didn’t, which would make us similar to gorillas. These giant herbivorous apes engage in battles over harems. However, our sex organs and our body size dimorphism (the sex difference between males and females) are nothing like gorillas and women’s bodies seem to have evolved as a sperm battleground. Instead of mostly competing via physical strength contests like gorilla males, our sperm is made for a race that involves competing against other sperm from other men and the human vagina is apparently a formidible racetrack able to store and sort sperm to some degree.
Unfortunately the legacy of the agricultural revolution has been STDs, pregnancies woman can’t support, lower sperm counts, and sexual repression. Condoms and birth control have solved some problems, but there is evidence that people who have sex without condoms are happier (I sometimes wonder if people promoting condoms as a solution to the world’s sexual ills have actually used them, but the authors also cite research that shows that women can aborb chemicals from sperm and get a mental boost from them) and that birth control affects woman’s ability to chose biologically compatible partners (and there is evidence that the children from these poor biological matches have reduced birth weight and impaired immune function). As far as abstinence education, data seems to show that expression of adolescent sexuality is associated with lower levels of violence. Paleos may also be familiar with the association between vegetarian grain-pushers like John Kellogg and sexual repression, but I was surprised to learn how he openly mutilated children to “protect” them from masturbating.
Gee? I wonder why high-fiber low-fat whole grain diets are so popular considering that many were developed to lower libido…unfortunately Ryan and Jethá don’t seem to get that part of the picture and repeatedly mention our ancestor’s healthy “low fat” diet. They also keep harping on a study that showed men eating massive amounts of beef have lower sperm counts, when that study was on the effect of eating feedlot beef pumped with hormones. To their credit, they also mention the ball-busting effects of soy, which are present no matter how it’s grown.
The book also point to some evidence that humans have adapted to deal with civilization’s demands on our sexuality. While it may seem laughable, apparently there is some truth to err… ethnic differences in penis and testes size for example, which they hypothesize might be related to cultural practices, though they admit this hasn’t been studied very well.
As for women’s sexuality being lesser than men’s, an idea that has been popular among evolutionary scientists since Darwin, with his own frigid wife, wrote “the female…with the rarest exception, is less eager than the male…” As a woman, you don’t have to convince me that this is untrue, but there remains a legion of men welded (and perhaps even attracted to) the idea of the chaste woman and, unsurprisingly, unable to locate the part of a woman’s body that would persuade them otherwise. If women are so uninterested in sex, why did physicians of yore devote so much time trying to stamp out the evil of female masturbation, even in the US resorting to female genital mutilation up until the 20th century. Luckily, some doctors changed tactics and the vibrator was born, but not as a cure for female dissatisfaction, but as a medical device to cure “hysteria.”
So what do humans want out of sex? It seems like we do enjoy intense pair bonds with other individuals…that eventually wane. The bane of marriage seems to be that sexual novelty is immensely exciting for humans. Ryan and Jethá seem to imply that swinging clubs might be a good solution for having an emotionally satisfying pair bond AND fulfilling sexuality. I suppose, but it underlines the difficult fact that humans have Paleolithic sexual desires in a world where children are expensive, women expressing themselves sexually are called “sluts,” and gonorrhea and other worse STDs are a real risk. The picture of modern sexuality painted in the book is a bleak one- of sexless marriages between men popping sperm-deforming antidepressants and hooked on internet porn paired with women with frustratingly low libidos struggling to juggle their career and children. Such marriages are not only bad for people's health because of the psychological effects; apparently sex with a new woman is one of the few tried and true ways to boost middle aged men's flagging testosterone. Fun.
I personally wonder how much low libido is connected with the inadequate diet and physical activity levels of modern humans. Evolutionary health aims to ask how we can use such science to make life better. In terms of sex I think our sex lives would certainly better if we would eat well, exercise, and be realistic about human nature. The authors don't really offer a solution and on their FAQ they say:
6. So you’re recommending the everyone should have an open marriage or not get married at all?
Definitely not. We’re not recommending anything other than knowledge, introspection, and honesty. In fact, as we say in the book, we’re not really sure what to do with this information ourselves. We hope Sex at Dawn advances the conversation about human sexuality so people can focus more on the realities of what human beings are and a bit less on the religious and cultural mythologies concerning what we should be and should feel. What individuals or couples do with this information (if anything) is up to them.
This book, while an excellent tour of human lustful behavior, is lacking on the murkier matter of love. But I definitely recommend reading it. It’s certainly fascinating, if anything.