The world has never been overpopulated with humans in any meaningful sense. It seems, though, that it is overpopulated with theoretical fears of overpopulation.
The appeal of the overpopulation myth is obvious—who doesn't love a simple, easily graspable idea that seems to explain a great deal? One such idea is the central biological insight that all animals aim to turn food into offspring. When a species' food increases, then its population grows as well; and when the food supply declines, so too do its numbers. This applies to everything from paramecia to parakeets.
Since humans are also animals that reproduce, biologists have extended that insight to us as well. This is the source of the overpopulation fears that have haunted learned experts from Thomas Robert Malthus 200 years ago to Paul Ehrlich today.
An extensive literature critiques the concept of human overpopulation. But it's apparently an idea whose time comes again, and again, and again, in all sorts of strange places. For instance, the 1990s saw a bad novelization of the concept in Ishmael, in which a telepathic gorilla recycles Malthusianism.
The latest iteration of this two-century-old idea comes from Duke University consultant Russell Hopfenberg, in an article called "Human Carrying Capacity Is Determined by Food Availability", in the November 2003 issue of the journal Population and Environment. Hopfenberg writes, "[T]he problem of human population growth can be feasibly addressed only if it is recognized that increases in the population of the human species, like increases in the population of all other species, is a function of increases in food availability."
Hopfenberg backs his argument by showing that global food supplies and human numbers both rise from 1960 to 2000. In 2001, Hopfenberg, writing with Cornell University ecologist David Pimentel in Environment, Development and Sustainability, further asserts that "if food production continues to increase, the world population is projected to increase to 12 billion in the next 50 years (based on current growth rates)." Hopfenberg's solution to skyrocketing human numbers is simple: "Cap the increases in food production and thereby halt the increases in population by means of a reduced birth rate."
So has the Malthusian case finally been proven? No. Hopfenberg's analysis makes the mistake of considering only global numbers. This hides a great deal of information. If we look on the regional level we see a very different picture than one of a relentlessly rising tide of human babies. Fertility does not correlate with food availability.
The countries with greatest access to food are, in fact, the countries with the lowest fertility rates. As the United Nations reports, 14 developed countries have fertility rates lower than 1.3 children per woman. (Replacement fertility is 2.1 children per woman.) The fertility rates in practically all developed countries are below the replacement rate. Clearly, food availability does not mean more children. More generally, as food security has increased around the world, instead of increasing as Hopfenberg's theory would suggest, global average fertility rates have dropped from 6 children per woman in 1960 to 2.6 today. And the rates continue to plummet. Sadly, in Africa, which has the highest current fertility rates, food production per capita has been declining for nearly 30 years.
If food availability really determined human reproductive capacity, Illinois farmers should have the highest fertility rate in the world. Instead, they have one of the lowest. Hopfenberg would reply that excess food produced in North America and Europe fuels population growth in the rest of the world. In some sense that is trivially true, but the strictly biological model that he says applies to people does not account for such phenomena. For example, deer in Virginia don't sacrifice their chances to produce fawns and ship their food to deer in Arkansas, nor do sparrows in New York forego nesting in order to supply food to Floridian sparrows. Individuals, not populations, reproduce.
The notion that capping food supplies will halt population growth is also trivially true, but not by the gentle means which Hopfenberg and Pimentel suggest, e.g., reducing human birth rates. Food shortages no doubt reduce fertility, but they also shrink population much more quickly by simple starvation.
Finally, Hopfenberg and Pimentel's projection that world population will reach 12 billion by 2050 is off. They simply extrapolate current levels of fertility, yet as we've seen, fertility rates are rapidly declining. The 2002 revision of the United Nations' World Population Prospects' median variant trend projects a world population of 8.9 billion by 2050. Given the rapidly falling global fertility rates, the low variant trend is more likely—and that projects a world population topping out at 7.5 billion by 2040, then beginning to decline. Perhaps Malthusianism will finally decline along with fertility rates.