DRAFT CLARIFICATION OF THOUGHT: Historical "Effective" Male & Female Human Population Sizes, & What They Mean
Joseph Henrich writes “fathers” & “mothers” where he should write “patriarchs who have left living male-line descendants” & “matriarchs who have left living female-line descendants” & so I fall down a sociobiology rabbit hole. Do I come out? You be the judge…
I do not—usually—like or resort to sociobiology arguments. They seem to me to read as just-so stories that read the author’s prejudices about today back onto an unknowable past of the environment of evolutionary adaptation, and of our adaptation in that environment, and what then grew out of it.
So I am not sure why I am finding this particular such argument so convincing. Perhaps it is just that it resonates with some of my prejudices about humanity today?
Let me back up:
I love Joseph Henrich’s books:
Henrich, Joseph. 2016. The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter. Princeton: Princeton University Press <https://archive.org/details/secretofoursucce0000henr>.
Henrich, Joseph. 2020. The WEIRDest People in the World: How the West Became Psychologically Peculiar and Particularly Prosperous. New York: Farrar, Straus and Giroux <https://archive.org/details/the-weirdest-people-in-the-world-how-the-west-became-psychologically-peculiar>.
That is not to say that I agree with them. But his books are perhaps the ideal books for me to read a very smart, very knowledgeable, well-intentioned person who thinks very differently from me about issues that we both care very deeply about and are profoundly interested in. The ideal person for me to learn from.
But yesterday I was rereading Henrich on polygyny from WEIRDest People, and ran into this sentence:
Geneticists have estimated the number of mothers vs. the number of fathers going well back into our evolutionary history. In a purely monogamous world, we’d expect the ratio of the number of mothers to fathers to be something close to one. Before agriculture, the data show that there was a pretty constant ratio of roughly two to four mothers for every father. However, a few thousand years after agriculture began, while the number of mothers was rapidly increasing as populations expanded, the number of fathers plummeted. That is, the number of fathers dropped, while the overall population was rising! At the peak of this climb, there were over 16 mothers for each father…
I know what he is talking about here, and this is simply wrong.
The human population has equal numbers of men and women. The vast majority of women who live long enough to achieve menarche become mothers. It is simply not the case that only ¼ to ½ of men who achieve adulthood become fathers. And it was definitely not the case that around the year -3000 or so only 1/16 of men became fathers.
What Henrich is talking about is this graphic from Karmin & al. (2015)<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4381518/>:
The top-left panel shows y-chromosome and the top-right panel shows mitochondrial DNA “lineages”.
All of us (men) have y-chromosomes that are those of Y-Chromosome Adam back roughly some 200,000 years ago, with whatever mutations of that have occurred since. Looking at the ensemble of y-chromosomes allows us to construct a tree by virtue of which y-chromosomes differ by one base pair, which by two, and so on. Similarly, all of us have mitochondria that are those of Mitochondrial Eve, back some back roughly some 200,000 years ago, with whatever mutations of that have occurred since. Looking at the ensemble of mitochondria allows us to construct a tree by virtue of which mitochondria differ by one base pair, which by two, and so on.