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I quote in full a passage from the book Is There Anything Good About Men?: How Cultures Flourish by Exploiting Men by Roy Baumeister, pages 63 – 64:

Counting Ancestors

Let’s return now to the question of what percentage of our ancestors were women. Yes, each baby has one mother and one father, so each baby’s parents were 50% male. But some of those parents had multiple children, and not necessarily always with the same partner. Every baby’s parents are 50% male, but you can’t extrapolate from that to conclude that today’s human population has an ancestry that is 50% male.

The correct answer has recently begun to emerge from DNA studies, notably those by Jason Wilder and his colleagues. They concluded that among the ancestors of today’s human population, women outnumbered men about two to one.

Two to one!

In percentage terms, then, humanity’s ancestors were about 67% female and 33% male.

To illustrate how this could be possible, imagine a desert island at the start of time with just four people: Jack, Jim, Sally, and Sonya. Thus the population is 50% female. Let’s assume Jack is rich and handsome, while Jim is poor and unattractive, so Jack marries both Sally and Sonya. Thus, Jack and Sally’s baby, Doug, has ancestors who are 50% female (i.e., Jack and Sally). The same can be said for Jack and Sonya’s baby, Lucy. But if you take Doug and Lucy together, their combined ancestors are 67% female (because their total ancestors are Jack, Sally, and Sonya).

Most people are surprised to hear that humankind today had twice as many female ancestors as male ones, because they thought it would be closer to 50:50. When experts hear about this, they are surprised too, but often for the opposite reason: They thought the imbalance would be even more severe. That is, they thought it would be maybe 75% to 85% female. Probably it was more severe through much of history, and especially prehistory. In many animal species, close to 90% of the females but only 20% of the males reproduce. The way the human population has ballooned in recent centuries means that most people who ever lived are either alive today or were alive recently, and in modern times the rule of monogamy has spread over large parts of the globe. In past eras, when polygamy (one husband, multiple wives) was the norm, the reproductive imbalance would have been even more severe. Hence whatever conclusions we draw about the differences between men and women based on the two-to-one ancestor difference are probably understatements. If we had done the research even just a few centuries ago, the ratio might have been three female ancestors to every male one, or four to one.

What does it mean that we are descended from twice as many women as men? It can be explained like this. Of all the people who ever reached adulthood, maybe 80% of the women but only 40% of the men reproduced. Or perhaps the numbers were 60% versus 30%. But one way or another, a woman’s odds of having a line of descendants down to the present were double those of a man.

Also, crucially, the majority outcome is different – the most common outcome of normal life. Most women who ever lived to adulthood probably had at least one baby and in fact have a descendant alive today. Most men did not. Most men who ever lived, like all the wild horses that did not ascend to the alpha male’s top spot, left behind no genetic traces of themselves.

That’s a stunning difference. Of all humans ever born, most women became mothers, but most men did not become fathers. You wouldn’t realize this by walking through an American suburb today with its tidy couples. But it is an important fact. I consider it the single most under- appreciated fact about the differences between men and women.

(italics in the original)

Here is a link to the paper mentioned in the text:

Jason A. Wilder, Zahra Mobasher, Michael F. Hammer: Genetic Evidence for Unequal Effective Population Sizes of Human Females and Males

I'm skeptical about the following claim from Roy Baumeister:

Of all humans ever born, most women became mothers, but most men did not become fathers.

I suspect a misrepresentation of the study.

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    @Oddthinking: how would you interpret "Of all the people who ever reached adulthood, maybe 80% of the women but only 40% of the men reproduced." ? – Ystar Apr 10 '17 at 11:01
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    You said yourself in an earlier revision: "the percentages are obviously just an example". We can conjecture other ratios over many generations, rather than it all happening in one generation. – Oddthinking Apr 10 '17 at 11:09
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    It's very hard to tell if a given man became a father. Motherhood is fairly obvious due to pregnancy and birth, but conception is rather harder to observe. – bdsl Apr 10 '17 at 12:53
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    What makes this worse is, I think Baumeister meant "Most men did not have descendants that survived to the modern day" rather than "Most men did not have a single child." Also, do we include boys who died before puberty? – Oddthinking Apr 10 '17 at 14:14
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    Relevant: tierneylab.blogs.nytimes.com/2007/08/20/… – Sakib Arifin Apr 10 '17 at 15:08
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This is not my area of scientific expertise. I cannot say if this study by Wilder et al is correct or not, but I can read the study and compare their conclusions to Baumeister's.

Wilder et al conclude that women outnumber men in human ancestry, but they do not conclude that the ratio is two to one. They make a different conclusion about a two to one ratio, which Baumeister incorrectly restates.

The study is based on a survey of the DNA of "25 Khoisan, 24 Mongolians, and 24 Papua New Guineans." The authors take DNA from a 2 specific places (loci) on the DNA of these people. One place is in Mitochondrial DNA (mDNA), which is inherited from the mother. The other place is on the Y chromosome, inherited from the father. They compare Y chromosomes to other Y chromosomes, to find out when the Most Recent Common Ancestor (TMRCA) was along the father's line. They do the same for mDNA for the mother's line.

From the introduction to the paper:

One of the most intriguing observations regarding the evolutionary histories of human mtDNA and Y chromosomes is that they are estimated to have very different times to the most recent common ancestor (TMRCA).

A short time to male TMRCA compared to female TMRCA is consistent with the claim. Wilder et al reviews many other scientists who also observe this.

Although the reasons for this reduction in variation remain unclear, these findings suggest that mtDNA and the NRY may be influenced differently by natural selection or sex-specific demographic processes.

Other scientists have suggested an explanation of Baumeister's claim due to natural selective forces. The paper refers to the specific type of natural selective forces as "recent positive directional selection."

We see no evidence that recent positive directional selection acting on the NRY is the cause of this disparity in TMRCAs, and we instead hypothesize that there is a widespread skew in the effective breeding ratio toward an excess of females over males among human populations.

Their conclusion uses a lot of technical language. The most plain English sentence I can find was,

Instead, we favor a hypothesis whereby sex-specific demographic processes act to reduce the male breeding population size.

In summary, Wilder et al. conclude that women outnumber men in human ancestry.

Baumeister makes claims that the authors do not make. He said:

They concluded that among the ancestors of today’s human population, women outnumbered men about two to one.

Wilder et al discussed a "twofold greater TMRCA." They also discussed how "male generation time" may be greater than female generation time, as an alternate partial explanation for this. "Twofold greater TMRCA" is not the same as "women outnumbered men about two to one." In some of these paragraphs it seems like Baumeister is just making up numbers. I don't understand the mathematics of TMRCA and effective populations well enough to give you better numbers.

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