Before we realized that crowds might have wisdom, demographers worried mightily about overpopulation. The recent renaissance in demography has seen a shift in focus. From the Economist:

The main concern of demographers in their heyday (the 1970s and 1980s) was high fertility and the total number of the world’s people. This was the period of The Population Bomb, a bestseller by a biologist, Paul Ehrlich, which argued that the world could not feed itself. An international family-planning movement sprang up. Top-down programmes attempted to control the total size of national populations. China’s one-child policy is the best known and most extreme of these.

Now though, as John May, formerly of the World Bank and now Georgetown University, shows in World Population Policies, the focus of demographers has switched from the overall size of populations to their composition—that is, to age groups and their relation to one another. Instead of high fertility rates, demographers study ageing, dependency ratios, the ‘demographic dividend’ (a bulge of working-age adults) and distorted sex ratios, which result when millions of parents choose the sex of their children, often by aborting baby daughters.

The result, suggests Mr May, is that demography is more complex, if less dramatic, than it used to be.”

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A 1972 UN film about threats to our environment, which features Paul Ehrlich. Also on hand: Indira Gandhi, Kurt Waldheim, Robert S. McNamara, etc.