David Puts – TEDx Talk TRANSCRIPT
Hi there. I could be wrong, but I think this talk may have the distinction of being the one talk in this series that ends with orgasm. But let’s not get ahead of ourselves.
Have you ever thought about the fact that you’re here, alive on this planet because every one of your ancestors reproduced? Every one, in an unbroken chain, all the way back to the first life on this planet, over 3.5 billion years ago. That’s a lot of reproducing.
And for the past billion years, your ancestors reproduced sexually. So sex is a pretty big deal. But you probably knew that.
But let’s talk about human mating. Why does human mating take the forms that it does? Why are we attracted to certain people? Why do we sometimes form long-term romantic relationships? Why do we sometimes cheat?
Now I don’t mean why consciously do we do these things. I don’t mean what happens in the brain to cause it. I mean, why did we evolve these feelings and these behaviors?
In other words, how did the underlying brain structures and brain chemistry contribute to our ancestors’ reproductive success so that those traits got passed on into the present generation while others didn’t.
Answering evolutionary questions like this is like being a crime scene investigator, we’re left with the evidence, and we have to try to establish what happened.
So let’s go back six or seven million years ago to our early ancestors. This is right after the split between our lineage and the lineage that would eventually give rise to chimpanzees. Now these were small brained apes, they walked on two legs, and males probably fought each other for mating opportunities.
We know this because males fight for mates in all of our closest living relatives, chimpanzees, orangutans, gorillas. And because males are larger than females when they fight for mates. And the fossil record indicates that our male ancestors were larger than females.
So males tend to be larger, more muscular, stronger, more physically aggressive, when they fight for mates. Our species has all the hallmarks of a species that’s experienced an evolutionary history of male fighting for mates.
For example, men have, on average, 60% more muscle mass, and 75% more upper body muscle mass, and those differences in musculature translate into large sex differences in strength.
The average man is stronger than 99.9% of women. These are data on hand strength, which is a good predictor of overall upper body strength, on over 600 men and women.
And as you can see, there’s a large sex difference. And in fact, not one of almost 400 women had as strong of a hand strength as the average man. So, men can open jars. And move furniture or at least two things that we’re good for. Who cares, right?
The answer is that men care. Men, especially young men, seem really concerned about figuring out who’s the toughest or strongest, or the most physically formidable, and sometimes they devise elaborate ways for determining this.
From early development, boys and men are more physically aggressive than girls and women all over the world, and this aggression sometimes results in violence.
Men have a virtual monopoly on same-sex homicides. In other words, men are vastly more likely to kill each other than women are to kill each other. These are data from every society from every time period in history for which data were available when the authors compiled them, on proportion of same-sex homicides that are male killing male.
And as you can see, the percentage is always close to 100%. On average, 95% of same-sex homicides are committed by males, and importantly, these don’t include war killings, which would bring the percentages even closer to 100%.
And from what evidence that we have, a dominance among men translates into mating and reproductive opportunities. So we’re a species that’s experienced an evolutionary history in which our male ancestors won mating opportunities through the use or threat of force.
In that regard, our apple has not fallen far from the evolutionary tree. But in other ways, human mating and reproduction are profoundly different from what we see in our close relatives, and they’ve changed a lot since our early ancestors.
For example, males in chimpanzees, orangutans and gorillas, spend time and effort competing for mates, but don’t spend much time with individual females and don’t provide resources. They don’t provide food for their offspring. So that’s a big change.
Although most human societies allow polygamous marriage, that is one man married to more than one woman. Even within polygamous societies, most marriages are monogamous. And in the average hunter-gatherer society, almost 80% of married women are monogamous, so that’s different.
And, importantly, men provide resources for their mates and offspring.
SO HOW DID WE GET THERE?
Well, in species where males fight each other for mates, dominant males indicated by the larger, darker male symbols here, tend to have more mating opportunities, and hence more offspring. And subordinate males tend to have fewer mating opportunities and are more likely to fail to reproduce.
So this sets up an interesting situation, because for subordinate males, it would be advantageous to attempt monogamy rather than winning lots of mating opportunities. One mate is better than none.
The problem is that in general, subordinate males cannot defend females from dominant males, and besides, females tend to prefer mating with dominant males for the genetic benefits, producing stronger, healthier offspring.
So what changed all of this was probably several transitions happening together around the same time. By about 2.5 million years ago, we had started to incorporate more meat into our diet. We know this from various lines of evidence, including — this is cool — stone tool cut marks on animal bones dated to 2.5 million years ago. That’s cool. I love this stuff!