If you were to able to travel back in time 50,000 years, abduct a paleolithic hunter from a river valley in southern France and haul him back to 21st century America, would he stand out in a crowd?

Depends on the crowd. He probably wouldn't blend in very well at the New York Stock Exchange. But dress him in shorts and flip-flops, hand him a backpack and he could probably stroll across any college campus in the country without attracting attention.

Human beings who lived 500 centuries ago were fully modern, virtually indistinguishable from us in fundamental ways. Their brains and bodies were physically the same as ours. They created sophisticated art murals, paintings, sculptures and buried their dead in a fashion that suggests they possessed ceremonial or religious traditions. They had developed the technology and navigational skills required to travel across broad expanses of ocean.

Paleolithic hunter-gatherers did not, however, domesticate plants or animals on a large scale. Nor did they live in large, sedentary communities. No one did until about 10,000 years ago when, suddenly and in multiple locations around the globe, agriculture and cities appear in the archaeological record.

The relatively abrupt and simultaneous rise of farming and urban settlement patterns suggests that the capacity to develop such innovations had been part of humankind's intellectual and behavioral bag of tricks for a long time. That capacity had lain dormant, however, awaiting some sort of catalyst to unleash it.

There's a pretty good theory as to what that catalyst might have been. If valid, it's potentially bad news for the well-groomed, suit-wearing descendants of Paleolithic cave painters.

This was one of the secondary but intriguing points made last week during the penultimate in a series of global warming programs at UC Santa Barbara. Thursday night's lecture and panel discussion featured journalist and author Elizabeth Kolbert, who turned her award-winning series of articles on climate change for the New Yorker into a book, "Field Notes From a Catastrophe: Man, Nature, and Climate Change," featured this spring in a campuswide reading program.

At about the same time that agriculture and urbanization appear in the archaeological record, the Earth entered a period of climate stability not seen at any time in the preceding 400,000 years. That's the span of time for which scientists have the most detailed record of global temperatures and atmospheric conditions, derived from the isotopic signature of frozen water and the chemistry of trapped air bubbles in ice cores pulled from the Greenland and Antarctic ice sheets.

What those ice cores reveal is a pattern of profound climatic instability during most of modern humanity's time on Earth. Every 100,000 years or so, the climate would begin to cool, probably the result of a recurring pattern in Earth's orbit around the sun. Ice sheets would grow, glaciers would advance and sea level would drop. Eventually, however, the climate would begin to heat up, at first slowly and then rapidly, the warming continuing until terminated by onset of another ice age.

Roughly 10,000 years ago, however, the pattern changed. Temperatures reached approximately the same high point that they had reached before each of the three previous ice ages, but then held fairly steady, with minor fluctuations.

And it is in that brief window of temperature stability that modern civilization was born and has flourished. It is entirely plausible that until then, human populations were forced to move so frequently to follow climate-driven shifts in food and water supplies that they could not develop social and technological systems requiring permanence.

About 150 years ago, modern humans began unintentionally tinkering with the climate system, setting in motion a trend toward warmer temperatures higher than any in the experience of our species that threatens to end this period of stability. The consequences may prove merely inconvenient for the richest nations, but for hundreds of millions of people in countries that lack the wealth and institutional capacity to adapt, the changes are likely to prove disastrous as food supplies collapse, fresh water becomes scarce and low-lying lands are inundated by rising seas.

There's a grim symmetry to this theory that human beings had to wait for a period of climate stability before they could develop the technology to destabilize the climate. And it offers a rather dismal prognosis for the future, which Kolbert expressed this way:

"An organism that depends on stability, but produces instability, can only survive for so long."

John Krist is a senior editor and Opinion page columnist for The Star. To read previous columns, visit http://www.johnkrist.com. His e-mail address is jkrist@VenturaCountyStar.com.