While the graphs lack detailed data about the recent past, we can see that from behavior modernity (50Ky) to agriculture (10Ky), the numbers were not that different. Then, about 10 000 years before agriculture, the number of women who reproduce increases drastically. About 5 000 years after agriculture, the number of men who reproduce takes a major dip then goes up dramatically.
First, when I say “male reproductive success”, I am not talking about the reproductive success of 1 particular male but of males in general. Greater male reproductive success would mean that a greater percentage of males would have children. Same for females.
1: Before behavioral modernity (50ky), is it reasonable to think that the difference in reproductive success was for similar reasons as chimpanzees; It comes down to which males fight, sneak and groom the best and females have little to no choice?
2: What could have caused the dramatic increase in female reproductive success some thousands of years before 10Ky?
3: What causes the dip in male reproductive success after 10Ky?
4: What caused male reproductive success to dramatically increase about 5Ky?
5: Is the fact that we have twice as many female ancestors as male ancestors almost wholly due to these pre-industrial era phenomena, especially the dip where there were 17 females passing on their genes for every 1 male passing on his genes?
If we were to look at modern societies, especially after WWII, what would be the reproduction success rates for males and females? If we take 100 Western women and 100 Western men, how many of each will have children?
The simple answer to the question ion the tread title is: Because one man can father way more children in his life than one woman can give birth to in her life.
Supposedly hunter gatherer societies were more egalitarian, but once agriculture was invented it created more unequal societies since you could build armies to dominate your own population. So in that situation, you’d expect the wealthy and powerful to monopolize all the fertile women. Thats probably partly why.
I’ve heard in times of environmental stress, the ratio of men who reproduce to women goes down, so fewer men reproduce and women prefer to reproduce with the minority of men who can best handle the environmental stresses. This is expected in a way, because if everyone has kids, then the genetic material of the next generation is no better suited to face the environmental stresses than the current generation. But if women only procreate with the 10% of men who are genetically fit and competent to face whatever environmental stresses are currently present, then the next generation will be far more fit and qualified to deal with it. If the environment changes (and it does), then women select different men who are fit. Being a computer nerd would get you nowhere in 1700AD, but in modern society it could make you a millionaire. Environments, and the skills necessary to beat environmental challenges, can and do change. Women look for traits that imply you can competently deal with the environmental stresses you are up against. And again, powerful men can just take whatever women they want.
So as a guess, it was a mix of growing inequality due to agriculture combined with environmental challenges that women unconsciously recognized only a small % of men were qualified to face.
Also, supposedly, this is why some major religions prohibit adultery. A society where only 1 in 17 men procreates is a society where 16 out of 17 men have nothing to lose. Their DNA is at a dead end, and keeping a society where you have to constantly stop those 16 men from overthrowing the system is very difficult.
If people are not pair-bonded, then men are literally competing with other men on the sperm level. There are lots and lots of men whose swimmers are not ideal, but eventually get the job done if they aren’t in competition with anyone else. Those are the couples you hear of who take more than a year to conceive a child, but eventually do, without any medical intervention. A man’s sperm count may be low, but not so low as to make him medically infertile, or he may have “poor motility,” which means the little guys don’t get where they need to go so well, but if a couple keeps trying, one may eventually get there.
However, if humans are not pair-bonded, and all the men in a tribe, or group, or clan, or whatever are having sex with all the women (more or less-- there are probably some taboos around mothers, sisters, whatever), the men with the highest quality sperm are going to do the vast majority of impregnating.
I mean, I know families, for example, in the Orthodox Jewish communities, who have upwards of 8 children-- I know families with 12 and 14 children-- because they don’t use birth control. On the other hand, I know families from the same community who have three children, and presumably the parents have the same views of birth control, and the children are widely spaced, so while it’s possible the parents used birth control on the sly, it’s more likely they just aren’t terribly fertile. (I do know an Orthodox family where the parents use birth control, because another pregnancy would be dangerous for the mother; they had three children in rapid succession, and no more).
That probably accounts for some of what we see in the historical record.
In many or most ancient societies certain high-prestige males had an enormous advantage in procreation. Some famous Asian rulers had thousands of women in their harems. Even if a low-status male had a child, the child would also be low-status and less likely to thrive. And even when the procreational advantage of high caste males was relatively small, if caste was inherited from the father, over many generations the caste would grow (like compound interest).
Y-chromosome studies have produced astounding confirmation. For example, a majority of Western Europeans are agnatic descendants of the single man who had the R1b-L151 mutation about 5000 years ago.
While I think that the 2 female ancestors to 1 male ancestor claim is reasonable, I’m dubious about the 17 to 1 claim. I’ve done some Googling, and I think that every article I’ve found about the 17 to 1 claim comes from a few days in 2015. Can anybody find a more recent article about the subject? Particularly, can someone find a more recent article from a scientific study which tries to confirm or refute the claim? I would expect other scientists to try to discover if this is true and if its conclusions can be generalized. I wonder if this claim came from just one study which may or may not turn out to be reliable, and the claim was immediately mentioned in many news stories.
As septimus put forth few very powerful men, Genghis Khan inclusive but not exclusively, may alone have a lot to do with whatever the actual skew is. The link details his point.
I see one thing lacking from the study. A lot of women died young (often from complications of childbirth.) Consequently, a man might marry several times in his life and father children with different wives.
In rural areas (and most areas were rural) the pool of potential mates was pretty small, and after a couple of generations, you’d start having second cousins, step cousins, and even half siblings getting married, all with common (male) ancestors.
In my own family tree, my father and his cousin married sisters. I haven’t tracked the lineage, but surely there are some great-x grandparents in common somewhere.
The OP talks about “women” but really we’re talking about girls - maybe 13-14year olds. They’re also property of their fathers.
I’d think the ‘elder’ / leader / priest of a community would get first doings with a fresh virgin in most cultures - an honour even, for the girl.
Child birth is going to be a messy business 10,000 years ago, the birth and/or later complications. So how many 13-14 years olds survived child birth for a second go, and who got seconds in that culture …
2010. The “the female-to-male breeding ratio, β” is estimated at more like
Another method in 2014 that demonstrated the skew is not as large as previously estimated. NRY = non-recombinant Y (male) and mtDNA = mitochondrial DNA (female).
However both that article and others do note that the last 10,000 years resulted in greater male expansion
Of course another factor is that they are measuring distinct Y vs. X; the male passes on either Y or X, 50-50. The female, one of two X. Every time a family has only daughters, that branch of Y is snuffed out. It’s probable, I assume, in a relatively closed clan with a smaller upper population limit that bit by bit the uniquely different branch of Y’s go extinct. Meanwhile, X’s are being spread far more widely and are less likely to be snuffed out. They measure mitochondria too, which are uniquely passed on by the woman. So the only reason mitochondria go extinct is if the woman has no female offspring who reproduce. Other than diseases which hit both sexes, the consideration is - the biggest threat to women was death in childbirth -i.e. they reproduced at least once. The biggest threat to men was violence, which did not necessarily wait until they reproduced. And I’ll go along with the property hypothesis - a woman of child-bearing years left widowed or unmarried would be claimed by the more dominant males or an available one, so often women had little say in their reproduction rate.
However, until the advent of agriculture, I assume dominant males, as in, “I can support multiple wives” was limited to maybe one or two males in a tribe. So can the winnowing be explained by selection since say, 10,000BC? Genghis Khan would like to think so. However, the lower variance in east Asia where potentates with massive harems were common, suggest this form of government was not a factor. Another hypothesis is that certain areas - say, moving into areas of the European peninsula - the first tribe and their ancestry became the ancestry for the whole area - a small founder group with a better chance for some y lines to go extinct.
Overall I agree with your post. But here’s a quibble about the snip above.
A woman who dies in childbirth was definitely pregnant to almost-term at least once. But …
There are lots of ways for a pregnancy that kills the mother to also kill the fetus/baby. Or for it still be alive and crying an hour later but unfeedable or abandoned by the end of the week.
Essentially, you (any you) have reproduced successfully only when one of your children has children. If your kids don’t reproduce, all you did was pointlessly extend the life of (some of) your genes by a few years after your own demise.
By that standard (plus many others) my parents totally failed with me.
One could take that to the extreme and say that you only count as having reproduced once your grandchildren have children, or your great-[sup]n[/sup]-grandchildren, for any value of n. Meaning that nobody ever reproduces if their species will ever go extinct, which eventually, they all will.
A more useful measure is to compare like to like. When looking at a newborn baby, calculate the odds that that baby will eventually grow up to have more newborn babies. When looking at an adult, calculate the odds that that adult’s children will eventually grow up to be adults themselves, and so on.
I recognized that as soon as I stack two turtles I’m pretty much committed to turtles all the way down. I just didn’t bother to fix the problem I noticed.
