Human Carrying Capacity and Human Health

192 T he issue of human overpopulation has fallen out of favor among most contemporary demographers, economists, and epidemiologists. Discussing population control has become a taboo topic. Yet, this taboo has major implications for public health. The silence around overpopulation prevents the global health community from making the necessary link between the planet's limited ability to support its people (its carrying capacity—see sidebar on following page) and health and development crises. In this article, I describe how popular thinking on population control has been shaped over the last 200 years, and how our failure to address the population explosion may be one cause of recent epidemics and social unrest. The question of human overpopulation and its relationship to human carrying capacity has been controversial for over two centuries. In 1798 the Reverend Thomas Malthus put forward the hypothesis that population growth would exceed the growth of resources, leading to the periodic reduction of human numbers by either " positive checks " , such as disease, famine, and war, or " preventive checks " , by which (in the absence of contraception) Malthus meant restrictions on marriage. This " Malthusian view " was rapidly accepted by most politicians, demographers, and the general public, and remained popular until fairly recently. Malthus's worst fears were not borne out through the century following his death in 1834—food production largely kept pace with the slowly growing global population. However, soon after 1934, the global population began to rise steeply as antibiotics, vaccines, and technology increased life expectancy. By the 1960s, concerns of a mismatch between global population and global food supply peaked— expressed in books such as Paul Ehrlich's 1968 The Population Bomb [1]. This book predicted a future scarred by increasing famine, epidemic, and war—the three main Malthusian positive checks. In 1966, United States President Lyndon Johnson shipped wheat to India to avert a famine on the condition that the country accelerate its already vigorous family planning campaign [2]. Johnson was part of an unbroken series of US presidents concerned with the harmful effects of rapid population growth in developing countries. This line extended (at least) from John F. Kennedy to Jimmy Carter. George H. W. Bush was also sympathetic to this view, prior to becoming vice president in 1981. But the 1970s surprised population watchers. Instead of being a period shadowed by calamitous famine, the new crop strains introduced by the " Green …