Dean's Column

This "Dean’s Column" is abstracted from remarks delivered at the Millennial Meeting of the American Philosophical Society, April 1999.

This has been a wonderful century. It wins the Most Valuable Century award hands down in this or any other millennium. Choose any indicator of human well-being—life expectancy at birth, infant mortality rate, literacy rate, per capita income, political participation—and the gains of the twentieth century exceed the gains of all previous centuries put together.

The advances are so persistent that I sometimes think they have acquired an air of inevitability, but of course they are not inevitable. Understanding how they occurred is one of the most important tasks of the social sciences. The evidence overwhelmingly favors the pivotal role played by the "march of ideas"—the greater understanding that we have achieved of the natural world and of the social world. I am convinced this is true in the improvements that I have studied most carefully: those in longevity. During the twentieth century, the germ theory of disease and its implementation in public programs and medical practice have for the first time given us secure protection against one another’s microbes. This is without question one of the monumental advances in human welfare, and great research universities like Penn are the most important institutions for developing, testing, and disseminating ideas such as these.

Not all ideas have fared well in this century. Last year marked the two hundredth anniversary of Thomas Malthus’ Principle of Population. In it, the eighteenth century economist and demographer argued that population growth will always tend to outrun food supply, expanding to the limit of subsistence and becoming constrained there by famine and disease. The betterment of the human lot, according to this view, would be impossible without stern limits on reproduction.

The twentieth century has not been kind to Reverend Malthus. This century’s unprecedented gains in well-being have occurred during a period of equally unprecedented population growth—a good indication of the poverty of the model he proposed. It is possible that our liberation from the constraints postulated by Malthus is only temporary. The most worrisome limitation is not the availability of land as Malthus believed, but rather the capacity of the biosphere to absorb rapidly expanding human by-products. The problem is not the mass of human beings. If everyone in the world gathered together in a circle and stood side by side, the radius would be only nine miles. The problem is the ecological damage that this little group is capable of inflicting on the planet.

But humans are also capable of turning the earth into English gardens and amber waves of grain. Con– trolling population size is surely one of the crudest means we have for affecting outcomes. We must focus on developing the incentives, the institutional structures, and the international agreements that are required to direct human activity in salutary ways. With thoughtful planning, the century to come can be even more remarkable than the century drawing to a close.