Having more female than male babies might result in more offspring in total for the species, but it also creates a strong genetic "advantage" (or, you could say a gradient in the fitness landscape) for the few individuals who themselves have more male children. This creates an evolutionary feedback pressure that results in the number of reproducing-age men and women to be approximately equal.

For example, imagine just for argument that the probability of the offspring being male or female is proportional to the number of sperm that carry either X or Y chromosomes. And imagine that this ratio is controlled by a gene, and that initially, the gene is such that across the whole population, 17 sperm carry an X chromosome for each that carries a Y chromosome. In this population, any male who has a mutation in this gene resulting in them producing a closer-to-equal number of X and Y sperm will have a reproductive fitness advantage, because they will have more male children amidst a majority-female population. Those mutations will therefore spread until the advantage disappears.

In order for 17-to-1 female:male ratio to be stable, you'd basically need to have a period of thousands of years in which, for whatever reason, 16/17ths of women do not reproduce. That's the exact opposite of the condition described in this article.

If there is a lot of "polygamy" (Genghis Khan levels), wouldn't it be more advantageous for upper-class parents to have male offspring (who will each have many, many children) and for lower-class parents to have female offspring (who will at least have children, unlike lower-class males)?

I mean, only if the upper-class and lower-class are separate gene pools, which I don't think is the scenario you are describing, at least not over the course of multiple generations. Not with offspring sex being randomly determined, anyway. If a "lower-class" female is mating with an "upper-class" male, then in which direction does the genetic fitness gradient point for the children of such a couple?

Remember that (mitochondria and Y-chromosomes aside) it's not the case that sons inherit their genes from their fathers and daughters from their mothers. The children of an upper-class father and a lower-class mother will have half of their genes from each parent regardless of sex or class.

Thankfully, that's no longer the case! The miracle of modern medicine means that we can take the DNA of the billionaire man, and the DNA of the billionaire man's wife, combine them in an egg from a second woman, and implant it in a third. The third brings the baby to term, a baby that has none of her disgusting lower-class DNA.

Okay, but now this is mixing up levels of abstraction. The sex ratio is determined based on the fitness gradient of the genes, but this is almost totally independent of the incentives that drive the individual. Most people, let alone billionaires, are actually not consciously motivated to pursue technological strategies to maximize their genetic fitness, even though mutations that induce those drives might theoretically be selected-for. Perhaps that's why most men don't become sperm donors, and most women don't urge their sons to become sperm donors. Billionaires in particular tend to be more concerned about their legacy, estate, and inheritance, and having a large number of heirs divides the pile they've worked so hard to accumulate. But to each their own, I guess?

Biology is a great equalizer.

Being upper class and lower class apparently doesn't have significant biological indicator to affect strategies such as these.

The poorest among our society are still mostly drawing in the same amount of calories, and feel happiness and sadness, age mostly in the same way.

There are no indications that billionaires are significantly happier/healthier than us - in fact these indicators are mostly tangential with wealth past a certain point.

> The poorest among our society are still mostly drawing in the same amount of calories, and feel happiness and sadness, age mostly in the same way.

maybe post-Industrialization, but a whole lotta people died of famine and disease before then, and the ones getting hit hard were the poorest.

The blunt answer is that evolution benefits from males killing other males for breeding rights much more than it would from every male getting a harem.

> If that were the case why did humans not evolve to have 17 times more female babies than male?

https://en.wikipedia.org/wiki/Fisher%27s_principle

While a son would have a much lower chance of reproducing, if he does, he'll reproduce a lot. I think that's the balance.

Worker bees. Not everyone needs to reproduce for the group to prosper.

I think we cannot compare humans with worker bees as these bees cannot reproduce. Basically, only the beehive is an complete organism.

For the latter part, I'd argue along the lines of the selfish genes (Dawkins): Not an organism wants to reproduce but rather the individual genes. They use the body as a vehicle for that. So it can still make sense for an individual to not reproduce and increase the chances of the same genes to be passed on (e.g., when an uncle without kids supports the kids of his siblings).

Because nature would rather roll the dice with 17 men, and get the best genes.

If you think this is inconceivably lopsided, wait until you see Elephant Seals mating on the shores of Point Reyes. Those bulls have one hell of a job come mating season.

But I'm pretty sure evolution still wants heaps of genetically diverse males to come out and compete in the reproductive lottery. Even if only a few of them win, they're the .. well, winners, genetically speaking.

With fewer participating at an existence level, you'd have would-be losers succeeding for lack of competition.

> The chance of a billionaire having a son is 65%

An acknowledged offspring. How many unknown kids do they father with mistresses? How many pregnancies get terminated? More darkly, how many wives of millionaires terminate pregnancies before 12 weeks when the fetus is female, but not male?

> More darkly, how many wives of millionaires [...]

Billionaires lead very different lives than millionaires

Typo. I meant billionaires. You probably figured that out, though.

Yeah sorry, I mostly wanted to make sure the B didn't get dropped in any replies to you

And why leave anything to chance? IVF makes it possible to pick the gender of the child, among other attributes. What's impossibly expensive for you and me is a Tuesday medical appointment at the wing of the hospital the billionaire bought.

The ideal sex balance of progeny depends on thousands of different factors, not just what fraction of males and females reproduce.

It doesn't seem like it was a continuous process; rather a temporary state.