Trivers–Willard Hypothesis
en.wikipedia.org
en.wikipedia.org
Thinking of it like a forest, women are the trees that create further forest and more life. The tendency for the forest to wish to cover the landscape with greenery and trees is normal, and once the forest is flourishing the focus changes to romping and playing.
Tragically and ironically, the 1 child policy in China was likely quite destructive because it caused so much stress and anxiety, uncertainty, and therefore mammalian ladies were likely creating mainly females, which were discarded in favor of males -- seen as the more important choice in times of scarcity -- in clear cross-facing against the grain of nature as she appears to play it in such times, according to the suppositions and supports of the hypothesis.
Billionaires have more sons, which is somewhat proof of this for humans
But there's so many other confounding factors (e.g. do billionaire men have more testosterone, as either a cause or an effect of their success, do they have children when they are older but the mothers are younger and so on) that it offers no evidence on its own.
In my experience, the primary consideration for most couples is the number of children. Then, if they want more than one, they want one of each. For whatever my personal experience is worth (mostly with middle and upper-middle class Coastal urban people).
It cited 60% male to female billionaire ratio on n of 350.
But, the methodology was to use google and Wikipedia for research so a more honest claim might be “male offspring of billionaires show up in search results more often.”
I suppose that factoid wouldn’t have been paid for by the publisher though.