It's well known that China's "one child" policy has led to a shortage of girls, leaving many young men unable to find wives. This week, though, I read in the paper that male birth rates are falling in some first-world countries, possibly because of environmental pollution, among other causes. All along, despite the higher number of boys conceived, fewer boys than girls have been born because prenatal loss of male babies tends to be higher. After birth, boys continue to succumb to death at higher rates than girls; males truly are the "weaker sex." Now, however, it seems that fewer boys are being conceived. So we could end up with a shortage of men in the developed world. Another demographic imbalance revolves around age. As an unintended consequence of population control, highly technological societies are ending up with "too many" older people in proportion to the young people needed to keep the economy functioning, especially in Japan and parts of Europe.
It's obvious that a society with too few women is in deep trouble, reproductively speaking. What are the likely sociological effects upon the status of women? Would they become highly valued and respected? Or would they be "valued" only in the sense of property to hoard and fight over? In the chilling theocratic society of Margaret Atwood's HANDMAID'S TALE, fertile women have become so scarce that they're forced to serve as breeding vessels (Handmaids) for a few wealthy, infertile couples. Another side effect of an excess of males, of course, is usually an increase in violent crime and other reckless behavior. A shortage of males, on the other hand, needn't pose a problem from a reproductive perspective. Given the necessary adjustment in sexual and/or parenting customs, one man can supply enough sperm to fertilized many women. From the perspective of women who want to marry and establish families, however, it's naturally a big problem. An extreme imbalance could lead to SF scenarios of men being held as pets or property by women rich and powerful enough to afford them. Or might the culture move in a retro direction and end up with a few powerful men possessing harems?
Too many old people? Might we (because I'm rapidly moving into that demographic) rule the world or at any rate the economy of developed nations, as we boomers supposedly do in the U.S. already? Or could the situation become so desperate that people past a certain advanced age—as in a little-read section of Swift's GULLIVER'S TRAVELS—would be effectively declared dead and stripped of their property rights to make room for the rising generations?
Optimistic SF writers such as Heinlein have often proposed fictional scenarios in which population pressures on Earth are relieved by extraterrestrial colonization. Would space travel ever become easy and cheap enough to remove any significant number of "excess" people from this planet? Historically, did the New World actually relieve population pressures in Europe? Or did the mere existence of an alternative for some people provide a symbolic "safety valve" that changed the balance in the Old World? I don't know enough history to have a legitimate opinion on that question, except that I know Ireland was severely depopulated by emigration in the wake of the potato famine in the 1840s.