Journalists are supposed to report “facts”. But, I have always maintained that journalists are stupid, and do not have the brains to know what the facts are. Journalists do not know that a lot of the unpopular truths that they think to be opinions are accepted as facts by their superiors. Because the average intelligence of journalists is lower than that of chimpanzees, they tend to believe that intelligence does not matter—that erudition does not matter. But, wishful thinking does not make this so. To see what I mean, read this report in The Times Of India:
But, is this what the study says? No. The journalist missed the point because he knew nothing about our evolutionary past.
The first big, basic male-female difference has to do with what I consider to be the most underappreciated fact about gender. Consider this question: What percent of our ancestors were women?
It’s not a trick question, and it’s not 50%. True, about half the people who ever lived were women, but that’s not the question. We’re asking about all the people who ever lived who have a descendant living today. Or, put another way, yes, every baby has both a mother and a father, but some of those parents had multiple children.
Recent research using DNA analysis answered this question about two years ago. Today’s human population is descended from twice as many women as men.
I think this difference is the single most underappreciated fact about gender. To get that kind of difference, you had to have something like, throughout the entire history of the human race, maybe 80% of women but only 40% of men reproduced.
Right now our field is having a lively debate about how much behavior can be explained by evolutionary theory. But if evolution explains anything at all, it explains things related to reproduction, because reproduction is at the heart of natural selection. Basically, the traits that were most effective for reproduction would be at the center of evolutionary psychology. It would be shocking if these vastly different reproductive odds for men and women failed to produce some personality differences.
For women throughout history (and prehistory), the odds of reproducing have been pretty good. Later in this talk we will ponder things like, why was it so rare for a hundred women to get together and build a ship and sail off to explore unknown regions, whereas men have fairly regularly done such things? But taking chances like that would be stupid, from the perspective of a biological organism seeking to reproduce. They might drown or be killed by savages or catch a disease. For women, the optimal thing to do is go along with the crowd, be nice, play it safe. The odds are good that men will come along and offer sex and you’ll be able to have babies. All that matters is choosing the best offer. We’re descended from women who played it safe.
For men, the outlook was radically different. If you go along with the crowd and play it safe, the odds are you won’t have children. Most men who ever lived did not have descendants who are alive today. Their lines were dead ends. Hence it was necessary to take chances, try new things, be creative,explore other possibilities. Sailing off into the unknown may be risky, and you might drown or be killed or whatever, but then again if you stay home you won’t reproduce anyway. We’re most descended from the type of men who made the risky voyage and managed to come back rich. In that case he would finally get a good chance to pass on his genes. We’re descended from men who took chances (and were lucky).
The huge difference in reproductive success very likely contributed to some personality differences, because different traits pointed the way to success. Women did best by minimizing risks, whereas the successful men were the ones who took chances. Ambition and competitive striving probably mattered more to male success (measured in offspring) than female. Creativity was probably more necessary, to help the individual man stand out in some way. Even the sex drive difference was relevant: For many men, there would be few chances to reproduce and so they had to be ready for every sexual opportunity. If a man said “not today, I have a headache,” he might miss his only chance.
Another crucial point. The danger of having no children is only one side of the male coin. Every child has a biological mother and father, and so if there were only half as many fathers as mothers among our ancestors, then some of those fathers had lots of children.
Look at it this way. Most women have only a few children, and hardly any have more than a dozen — but many fathers have had more than a few, and some men have actually had several dozen, even hundreds of kids.
In terms of the biological competition to produce offspring, then, men outnumbered women both among the losers and among the biggest winners.
To put this in more subjective terms: When I walk around and try to look at men and women as if seeing them for the first time, it’s hard to escape the impression (sorry, guys!) that women are simply more likeable and lovable than men. (This I think explains the “WAW effect” mentioned earlier.) Men might wish to be lovable, and men can and do manage to get women to love them (so the ability is there), but men have other priorities, other motivations. For women, being lovable was the key to attracting the best mate. For men, however, it was more a matter of beating out lots of other men even to have a chance for a mate.
Tradeoffs again: perhaps nature designed women to seek to be lovable, whereas men were designed to strive, mostly unsuccessfully, for greatness.
And it was worth it, even despite the “mostly unsuccessfully” part. Experts estimate Genghis Khan had several hundred and perhaps more than a thousand children. He took big risks and eventually conquered most of the known world. For him, the big risks led to huge payoffs in offspring. My point is that no woman, even if she conquered twice as much territory as Genghis Khan, could have had a thousand children. Striving for greatness in that sense offered the human female no such biological payoff. For the man, the possibility was there, and so the blood of Genghis Khan runs through a large segment of today’s human population. By definition, only a few men can achieve greatness, but for the few men who do, the gains have been real. And we are descended from those great men much more than from other men. Remember, most of the mediocre men left no descendants at all.
Let’s start with an assertion in the speech that troubled many readers: we have twice as many female ancestors as male ancestors. Dr. Baumeister called it the “single most underappreciated fact about gender.” Critics responded that it couldn’t be true because every child has a father and a mother. Some readers acknowledged that we might collectively have fewer male ancestors than female ancestors, but they insisted that any individual must have an equal number of males and females in his family tree. And a lot of readers demanded to see the evidence for the assertion.
Rest assured that neither Dr. Baumeister nor I believes in virgin birth. It does indeed take two to tango. But we still have more female ancestors. Before getting to Dr. Baumeister’s explanation, let’s hear from Jason Wilder, a biologist at Williams College who came up with some of the genetic evidence cited by Dr. Baumeister. (You can read a paper by Dr. Wilder here.) And here’s Dr. Wilder’s response to the comments by disbelieving Lab readers:
I’ve run into all sorts of problems when explaining our finding that the breeding sex ratio is skewed in favor of women. (The most common response: “More women have children than men? Duh, of course.”) I’ll explain very briefly the methodology of our study and how we interpret the results.
In a nutshell, we examined the amount of genetic variability on the Y chromosome (which is inherited by males solely from fathers) and mitochondrial DNA (inherited in both sexes solely from the mother). According to population genetic theory, the amount of variation observed among any set of chromosomes surveyed in a population is proportional to two factors, the rate of mutation and the size of the population (in terms of numbers of reproducing individuals). If we factor out differences in the rate of mutation, then any leftover difference in the amount of variation between two samples of chromosomes should be due to differences in the sizes of the populations from which they are sampled. Applying this method, we were able to estimate the relative size of the female and male human populations (from mitochondrial and Y chromosome variation, respectively). We found that the breeding sex ratio is about two females per male.
On average (and over evolutionary time), any given human female has been more likely to reproduce than any given male. Said another way, males have had a higher variance in reproductive success than females. As a consequence, more different females have contributed to the modern gene pool than males. Rather spectacular examples of this phenomenon have been inferred from historical times using genetic data. Asian conquerors (such as Genghis Khan and Giocangga) and their male relatives appear to have made a vastly disproportionate contribution to modern Asian populations. Niall of the Nine Hostages seems to have had a similar effect on the gene pool of the British Isles. These types of events, where one person (or set of related individuals) experiences tremendous reproductive success, can have an effect on the gene pool that lasts for many generations. On the other side of the equation, we have to infer that there are many more males than females who do not successfully reproduce at all.
So what does this mean for the number of males and females in any individual’s family tree? “I would argue,” Dr. Wilder replied, “that it is more likely that every individual has a greater number of unique female than male ancestors. I suspect that the trouble is in convincing people that their family trees do not continually bifurcate back in time. Ultimately the constraints of an historical breeding population of finite size causes reticulations in the tree. These reticulations will more often involve male than female ancestors.”
Now let’s hear from Dr. Baumeister on the questions over our ancestry:
Yes, each baby has one mother and one father, but it is nonetheless possible for combined ancestors to include more females than males. Here is a simple example. Suppose an island contains two men, Bob and James, and two women, Sally and Maria. Bob is rich and charming, while James is poor and uncouth, so both women marry Bob. James remains celibate. Soon, Sally gives birth to Doug, and Maria gives birth to Linda. Count the ancestors so far. Doug’s parents (Bob and Sally) are 50% female. Linda’s parents (Bob and Maria) are also 50% female. But added together, their parents are 67% female (Bob, Sally, and Maria).
Next, suppose Doug marries Linda and they have a baby named Max. Max himself now has more female than male ancestors: Linda, Doug, Bob, Sally, and Maria. Thus, it is possible even for one person to have a family tree that is not 50-50. This is true even though we started with equal numbers of males and females (but poor James was a dead end) and though each child has one mother and one father.
In actual life, incest taboos might have prevented Linda from marrying her half-brother, but if a couple generations had intervened, there would have been no objection. We have more female than male ancestors because of some men having multiple mates (and other men having none) and because of some mating partners having the same male ancestor.
Some of you wrote to ask for sources to look up. There was a fair amount of coverage in the popular media back around September 20, 2004 (e.g., “Ancient man spread the love around”), and you can still find those stories online or elsewhere. They explain the basic findings reasonably well. In contrast, the primary sources are quite technical to read. Look for works by Jason Wilder as first author (Nature Genetics, October 2004; Molecular Biology and Evolution, 2004) and a somewhat more accessible commentary by Mark Shriver in the European Journal of Human Genetics (2005). None of them really treats the psychological implications of the difference, focusing instead on the molecular biology of it and possible implications for demographic spread. But that’s part of what made me label the finding “the most underappreciated fact about gender.”
And as for the 80%-40% numbers, admittedly those are chosen somewhat arbitrarily. It could have been 60%-30% or 70%-35%. The only definite thing was that twice as many previously living women as men have descendants alive today. It depends a bit on how you count, especially because in the past a great many people died before adulthood (so you get higher proportions if you talk about all adults than if you talk about everyone who was born). The crucial implication was that for adult women, the odds of passing on genes were much better than for adult men, and so different strategies were needed.
Some of you wondered whether people really cared that much about having children. Were men taking risks in order to reproduce? This is a point that sometimes confuses people. Sure, there may have been many men and women who didn’t care whether they had children or even who actively wanted to avoid having children. (There still are!) The thing is, they did not leave many descendants. By definition, we are descended from people who did manage to reproduce. Maybe the risk-taking men had no thoughts of having children. But as long as they ended up having more children than the risk-avoiding men, then today’s descendants will have inherited the traits of the risk-seekers, not the risk-avoiders.
Post Script: Read Roy F. Baumeister’s “Is There Anything Good About Men? How Cultures Flourish by Exploiting Men”. It is the best work on gender I have ever read.