Do we have more female than male ancestors?

Question

I have read a claim in several sources, including a New York Times article by John Tierney, that we have more female ancestors than male ancestors.

"Citing recent DNA research, Dr. Baumeister explained that today’s human population is descended from twice as many women as men. Maybe 80 percent of women reproduced, whereas only 40 percent of men did."

While this may seem unintuitive, it is possible due to pedigree collapse and a lower rate of male repoductive success. A lower rate of male repoductive success (i.e. males were less likely to survive to reproductive maturity) in combination with pedigree collapse may mean that our total number of female ancestors can exceed the total number of male ancestors.

Is this true for a person with predominantly European ancestry? I would particularly like to see genetic or demographic evidence that supports or refutes this idea. If true, it would also be useful to quantify the ratio of male to female ancestors at a given generation level - in other words, roughly how significant is this effect on a genealogical timescale?

Answer 1

This article is not talking at all about pedigree collapse or male reproductive rates.

What Baumeister states in his book Is There Anything Good About Men is that "DNA studies, notably those by Jason Wilder and his colleagues ... concluded that among the ancestors of today's human population, women outnumbered men about two to one." He then states this means that "humanity's ancestors were about 67% female and 33% male."

He then gives an example of a desert island with 4 people, two male and two female. One male has a child with both females. The other male does not. We now have two children. They are descended from two females and one male. 67%, 33%. John Tierney, in the article you refer to, expands this to a Gilligan's Island example going one more generation and showing a grandchild with 3 female ancestors and 2 male: 60% to 40%.

What this is doing is going back to the very first ancestors. The work by Jason Wilder (e.g. Genetic Evidence for Unequal Effective Population Sizes of Human Females and Males) was related to finding the Y-chromosomal Adam and Mitochondrial Eve.

The Y-chromosomal Adam article explains that there was a discrepancy in time depths with mt-MRCA most recent common ancestor living 150,000-200,000 years ago, but the Y-MRCA living 84,000 years ago. It states: "One explanation given for this discrepancy in the time depths of patrilineal vs. matrilineal lineages was that females have a better chance of reproducing than males due to the practice of polygyny. When a male individual has several wives, he has effectively prevented other males in the community from reproducing and passing on their Y chromosomes to subsequent generations."

So Baumeister is not stating anything about generational levels. It is not in any way trying to state that the total number of female ancestors someone will have will be twice as many as the number of male ancestors they have. It is only referring to humanity's set of most recent common ancestors, and it is only "one explanation" for a discrepancy in the MRCA depths.

Polygyny was common in primitive and biblical times, but became rarely practised after that. And even if you had some polygyny, the practise is no longer widespread enough to prevent the other males from finding a partner. So that practise will not be a cause of misbalance in the number of your male versus female ancestors in your genealogical research.

Answer 2

You keep thinking linearly, this can be seen statistically (it is genetics after all). Take number of generations, we hear 25 used as an average, but parents are not always a similar age and definitely not in the past. So as a simple example say a generation between a father and son averages 30 years while a generation between a mother and daughter is just 15 years (far more common in the past), it is easy to see how overtime you end up with more female ancestors. It is just a matter of time. Of course not along the same line, but you have ancestors from multiple branches and each line progresses at it's own pace, figuratively speaking.