What I learned about human evolution in a book about sex

Sex at Dawn: How We Mate, Why We Stray, and What It Means for Modern Relationships was an interesting book that sparked many interesting conversations in my life. (Yes, animals do practice oral sex.)

Once I got over being angry about the final chapter that explains why all that history excuses why men cheat but not why women do, I realized the thing that stuck with me was not about sex but about how farming has changed our health.

Hunter gathers live to be about 70 years old. It was only after we introduced farming and land ownership to the equation that life expectancy dropped drastically in the middle ages. The book had a number of theories about why hunter gathers lived longer:

  1. Fewer children. They had fewer children due to delayed puberty. Hunter gathers ate a lot less fat and were generally a lot thinner. This meant that puberty was delayed and women did not start having children until later in life. Having a lot of children tends to decrease a woman’s life expectancy.
  2. Fewer children. They had fewer children because they breast fed longer. Because hunter gathers did not have animals to produce milk, they could not switch young toddlers to animal milk, so women breast feed their children longer. Breastfeeding women are less likely to get pregnant. Having less children increased their life expectancy.
  3. Less disease. Hunter gathers were less likely to die of disease because they lived in smaller groups. Hunter gathers lived spread out and had contact with only a small group of people on a regular basis. Farming communities could feed more people in a dense area. Dense areas are more likely to spread disease to more people quickly.
  4. Better diet. Hunter gathers, based on their bones, did not go through long periods of malnutrition like medieval village dwellers did. When food wasn’t good, they moved. Village dwellers had to depend on crops and if the crops were not good, they had no easy backup supply. Also villagers ate many more grains which had less calories and protein than what hunter gathers ate.
  5. War. Hunter gathers did not often fight wars nor even skirmishes. Wars came about when people settled and fought over land and possessions. The authors spent quite a bit of time on this one as they believe that hunter gathers have unfairly gotten a reputation for being violent.

The book goes on to theorize that the more promiscuous women are in a culture, the more peaceful it is. The authors had a number of reasons. Among them was that societies with promiscuous women don’t fight over women as possessions and they don’t promote their children over others. Since none of the men knows whose children are whose, they help all the children out. I think that’s a lovely idea but not sure why it makes sense for only one gender.

The book also briefly touched on how land ownership changed many things in our culture, including sex. According to the book, when landownership became a thing, people became preoccupied with making sure their land stayed in their family. They became more concerned with making sure their kids were really their biological kids; they became much more concerned about who their partners were having sex with. Since land was all owned by men, and women don’t have much doubt about whether a child is theirs or not, men spent a lot more time and energy making sure their female partners did not have sex with anyone else.

There were a lot of other interesting points in the book, many much more related to the title — things like why women are verbal during orgasms, why human male penises are so large compared to other primates and even theories on why different races have different size testes.

I recommend you read it if you are interested in all those things. I’m going to go learn more about the evolution of our society, hunter gathers and cities.

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