ONE day in October 1990, the iconoclastic economist Julian L. Simon walked out to get the mail at his house in the Washington suburb of Chevy Chase, Md. In a small envelope sent from Palo Alto, Calif., he found a sheet of metal prices, along with a check for $576.07 from the biologist Paul R. Ehrlich. There was no note.

Ten years earlier, Mr. Simon and Mr. Ehrlich, joined by two scientific colleagues, had made a wager on the future prices of five metals: chromium, copper, nickel, tin and tungsten. The bet — in which the loser would pay the change in price of a $1,000 bundle of the five metals — was a test of their competing theories of coming prosperity or doom.

For years Mr. Ehrlich, the author of the landmark 1968 book “The Population Bomb,” had warned that rising populations would cause resource scarcity, even famine, with apocalyptic consequences for humanity. Mr. Simon, who died in 1998, optimistically countered that human welfare would flourish thanks to flexible markets and our collective ingenuity.

Mr. Ehrlich believed the metal prices would rise over the decade; Mr. Simon thought the prices would stay stable or even drop. Mr. Simon won: the prices of the five metals in 1990 hovered at around 50 percent of their 1980 levels, even as the world population grew by 800 million.