Today, a progress report. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

By the time this program reruns, it may well be ready for updating. That's because recent studies have been causing an old question to shift under our feet. "Where did we modern humans, we Homo Sapiens or Cro-Magnons, come from -- and when?"

For over a century we'd thought that our technological species had arisen in Europe and the Near East some forty thousand years ago and then (rather quickly) displaced the Neanderthals.

It's clear that we began creating sophisticated cave painting and tool-making; and that we have, ever since, been the only human species. But the search for our mutual origins has recently shifted away from Europe to artifacts and remains in Africa.

Now, in South Africa, we are finding seventy-thousand-year-old delicate bone awls and a seventy-seven-thousand-year-old piece of ochre engraved with a design. Most amazing are ninety-thousand-year-old items from the Congo. An early harpoon for spearing fish has sweptback hooks along its shank. Several flat beads look like small metal washers.

So the great explosion of art and technology clearly began, not in Europe, but in Africa. DNA evidence points back to the remains of a modern-human African female whom we name Eve. She's about twice as old as the oldest of these fine artifacts.

The current mystery is no longer where these people and their art came from, but how they made their way out of Africa. And here, two competing routes have been on the table. Both begin with modern humans who had moved north into Ethiopia. From there, the favored route was up through Suez and into the Holy Land.

But DNA evidence supports the second route. It suggests that modern humans crossed the southern tip of the Red Sea (where Ethiopia almost touches Yemen today) and they continued through Arabia and Persia into India. Then they migrated both eastward and back to the northwest and Europe. They reached Australia some sixty thousand years ago, maybe before they got to Europe.

New York Times science writer John Noble Wilford points to two factors that archeologists think caused the sudden technological explosion that these people created. One was population; the other, adaptation. Population growth drove migration, and it drove people to go after harder-to-catch game. When there are enough of us to eat up all the slow-moving turtles, we must either move or invent means for hunting more elusive animals.

Those same factors work in yet another way. As populations increased, we sought out means for expressing our individual selves to one another. "I am me!" "Here is a picture of what I am thinking." "Here is my new invention." That's very important. It's the reason that art has always preceded utility, in invention.

So we came out of Africa. Eve really did move off to the east of her Eden. We carried our art -- our inventions -- with us, and, for better and for worse, we took over the world.

Cain, by Fernand Corman, 1880
(Artist's impression of Cain's expulsion)

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Wilford, J. N., When Humans Became Human. New York Times, Science Times, Tuesday, Feb. 26, 2002, pp. D1 and D5.