I just recently realized that this year is the 40th anniversary of Garret Hardin's seminal essay "Tragedy of the Commons" (ToC).
Hardin, who died in 2003, argued that the Earth is commons, and that we're rapidly overpopulating it. (Oddly, Hardin did not cite Malthus.) The tragedy is that there is no technical solution to the problem, that is, no way to win without radically revising the game itself. Voluntary restraint in childbearing would lead to those voluntarists being outbred by those who didn't restrain themselves. The only solution, therefore, is "mutual coercion, mutually agreed upon," because "the freedom to breed is intolerable." Because of ToC's environmental implications, Hardin inarguably has had more influence in the social sciences than any other biologist.
Certainly population growth since the 1960s has been tremendous, as is shown in this chart. But the rate of growth has declined, so we will stabilize at some point in the future.
Source: United Nations.
But as can be seen in the second graph, population growth is almost wholly a function of underdevelopment. As people grow wealthier, they tend to shift along the r-k reproductive continuum from a more r-type strategy, to a more k-type strategy, resulting in fewer childen, and slower population growth.
Source: United Nations. Found at Population Reference Bureau.
The critical problem in Hardin's argument appears to be his assumption that having more children is always individually rational (or, from the biological perspective, always selectively advantageous). But philosopher Stephen Gardiner persuasively argues that this assumption is both theoretically erroneous, and not supported by empirical data.
One of the predicted outcomes of overpopulation was pressure on available resources. To that end, Paul Ehrlich, who famously predicted that much of the world would starve to death in the 1970s, accepted a bet with economist Julian Simon, concerning the future price certain resources (Simon let Ehrlich select them, and Ehrlich chose 5 metals). If they became scarcer due to population pressure, the price would increase. Ehrlich lost the bet, and just recently economist Mark Perry has argued that if the bet had been repeated between 1990 and 2000, Ehrlic still would have lost.
Most people, including me, are worried about overpopulation of the Earth, but empirical evidence that we've reached or exceeded carrying capacity is scarce. But I think the whole issue is compelling enough that I've begun planning a 40-year retrospective symposium at my college. It's much too early to say whether I'll pull it off, but I think it would be very interesting to get a variety of perspectives on Hardin's argument with the benefit of 40 years of thought and accumulated evidence.