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Overpopulation question is complex, scientist says

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Whether Earth faces a catastrophic problem with overpopulation isn't a simple question. The answer depends on both physical constraints and human choices, according to one of the foremost experts on population.

Joel E. Cohen, presently on a teaching assignment at Harvard University but otherwise a professor at Rockefeller and Columbia universities, outlined the complexities involved in estimating the world's ability to support humans Tuesday night at the University of Utah Fine Arts Auditorium.His talk, "How Many People Can the Earth Support?" was the first of this year's Frontiers of Science lecture series. About 300 attended, filling the auditorium.

He noted that the world has undergone a startling population explosion, with the total number of humans expected to pass 6 billion this year. The population doubled in only 40 years.

Meanwhile, over the past 50 years, estimates of the total number of humans the planet can support have varied wildly, Cohen said. What isn't debatable is that the gap between the standard of living in rich countries with relatively slow population growth and poor countries, where the population is booming, is a wide one indeed.

In 1960, the wealthiest 20 percent - people in the developed countries - collected 72 percent of the world's overall income. The bottom 20 percent got only 2.3 percent. A person in the top 20 percent had 30 times the wealth of one in the lower group.

By 1972 the gap widened to 32 times; by 1980, 45; and in 1991, it was 60. In other words, for every $1 in income a native of Africa made, an American made $60.

Demographics show that food supply is not a good indicator of how many people an area can support. "Africa has among the lowest levels of food . . . and yet they have the most rapid population growth," he said.

How can 750 million people in the world live without enough to eat "while food prices have dropped by half?" he asked. The answer is that the poorest one billion people don't affect the world's prices because they are "economically invisible," he said.

The fact that food prices are low does not indicate that there is no scarcity, Cohen added.

Humans have increased so vastly in number that the species has become equivalent to a geological force, remaking the face of the Earth, he said. Water impounded by dams or in man-made reservoirs amount to five times the total amount of water in the world's rivers and streams, he said.

With people sharing resources, he said, "there is no longer any `away' to throw things away to." Carbon dioxide pollution from a car in Manhattan and carbon dioxide spewed from a coal-fired power plant in China mix in the atmosphere within six days.

While these trends are continuing, the overall fertility rate is dropping, even in some of the most disadvantaged countries. Contraception is responsible for the drop. He said people will practice birth control regardless of what their religious leaders teach.

Meanwhile, humankind is mowing down tropical forests and causing animal species to die out. Cohen described visiting a display of stuffed, extinct birds in an English museum: "It is like walking through a room of ghosts - disapproving ghosts."

"How many people can the Earth support is an incomplete question," he said. A more complete query takes factors like these into account:

- How many can it support in terms of human well-being? In terms of what technological status, and which political institutions? With what economic consequences? In what physical and cultural environment? With what sorts of domestic and international arrangements?

- How many can it support with what variability or stability? How many can it support in terms of risks or robustness? For how long can it support that many? And with what values, tastes and fashions can those people survive?

To cope with the burgeoning worldwide population, people should understand the complicated relationship between the physical constraints of the planet's carrying capacity and the choices that people must make.

"I would argue that neither panic nor complacency is in order," he said. "Forthright action now might make some of the coming choices easier."

During a question-and-answer session following his talk, Cohen advocated improving the world's economic climate through greater trade between developed nations and poorer countries.