I found an interesting article written by David Bauer with a very detailed discussion of gender demographics. I highly recommend it. For a free article, it is quite informative. Bauer shows that there are more men than women on the earth mostly due to the practices of China and India – where a preference for sons has resulted in many female abortions (and female infanticide). This practice was exacerbated by China’s one child policy because many Chinese would kill their child if the child was a girl so they could then be allowed to try for a boy. Bauer’s collection of statistics also shows that most developed countries have slightly more women than men because women tend to live longer.
Bauer gave some reasons why women live longer than men, but another reason is simply because men engage in more risky behavior than women. This is not just human behavior, it is true in the animal kingdom as well. For example, male monkeys in Japan will play a game where they try to cross a busy highway despite (or because of) the risk of death. Female monkeys do not play such games…
Bauer points out gender differences in migration, especially illegal migration. I had not considered this before, but it makes sense and has implications for entire nations. For example, Bauer showed that Mexico now has a larger percentage of females because so many of their males are illegally in the United States. It makes one wonder how much of the crime in Mexico is due to the fact that so many men – who traditionally serve as defenders of the home – are away.
While it was a bit outside his topic, I would add the role of social norms to his discussion. Social norms influence population growth by putting an effective cap on family size in cultures where reliable birth control is available. For example, a few generations ago most Americans thought four kids was the ideal family size. Once reliable birth control was commonplace, four became the cap for most families – people who reached their ideal family size stopped at that point. Since all families did not reach that point, many people saw families with less children and that became the norm for the next generation. China is experiencing the power of social norms right now – the Chinese government has seen the error of their ways concerning the one child policy and this policy is no longer rigidly enforced and may be going away. However, since a generation of Chinese has grown up seeing families with only one child, this is now the social norm. Even if the Chinese government paid parents to have more kids, they will find most families will only want one child.