Current interest in catastrophe may arise from primal instinct

0 Comments | Insight on the News, July 29, 1996 | by Larry Witham

Twister is a big hit and Twentieth-Century Fox hopes Volcano will pack movie theaters next year. Why so much interest in disaster? Scientists now think humans evolve in response to ecological crisis.

Americans are having a love affair with catastrophe. Movies about tornadoes are blockbusters. Scientists are predicting global overheating and the death of the rain forests. Now a group of paleontologists is proposing a cataclysmic theory about the origins of human life -- how it was that the first upright, two-legged, big-brained creatures evolved into Homo sapiens.

"We were born in an ecological crisis," said Johns Hopkins University paleontologist Steven Stanley at a recent Smithsonian Institution lecture. "You might say that global change is not all bad."

The ecological catastrophe -- gauged in hundreds of thousands of years -- was precipitated by the appearance of the Isthmus of Panama about 3.5 million years ago, according to Stanley. The small neck of land, pushed up by a volcanic thrust, sealed off the Atlantic from the Pacific and stopped the warm currents that used to reach the polar region. Glaciers moved toward Africa, killing the forests and forcing apelike hominids to survive in the cooler, dryer savannahs. "Our ancestors had to be fully on the ground before we could develop a big brain," said Stanley, whose theory is expounded in his new book, Children of the Ice Age: How a Global Catastrophe Allowed Humans to Evolve.

Anthropologist Rick Potts, director of human-origins research at the Smithsonian, also emphasizes the dramatic environmental events that triggered human evolution. "Periodic reversals in environmental trends were more important" than gradual cooling of the Earth, Potts said during a lecture at the recent North American Paleontological Convention, arguing that dramatic shifts from hot to cold produced a supremely adaptable upright hominid. He fleshes out his theory in a new book, Humanity's Descent: The Conse-quences of Ecological Instability.

Both Potts' and Stanley's "punctuated" theories of human origins contrast with earlier conventions depicting human evolution as a gradual process. Charles Darwin, for example, argued that apes came down from the trees, walked on two legs and developed their brains by using tools and inventing a complex social life. The geologist Charles Lyell postulated that the Earth built up gradually over eons -- an idea amenable to the Victorian liking for incremental progress and improvement in all things.

But the idea of gradual evolution, even in the context of new fields such as genetics, failed to generate a satisfying history of creation. Some scientists began to reshape pre-Darwinian theories, including those of creationism and the Noahdic flood. Berkeley geneticist Richard Goldschmidt, for example, suggested in the 1940s that macro-mutations could create "hopeful monsters," such as a bird from a lizard egg, only to become a laughing-stock.

During the last two decades, however, dramatic change has become a theory in itself. Geologists, astrophysicists and paleontologists all have argued that a giant meteor or comet killed off the dinosaurs when debris from its impact dirtied the atmosphere and cooled the Earth's temperature.

Meanwhile, the public has embraced "old-fashioned" notions as well. The most recent Gallup Poll, from 1993, found that 49 percent of respondents agree that "man was created pretty much in his present form about 10,000 years ago." The National Science Board's 1996 science indicators, released this spring, included a public survey of scientific knowledge in which 58 percent of those questioned did not know -- or did not believe -- that "humans developed from earlier species of animals."