The first human ancestors appeared between five million and seven million years ago, probably when some apelike creatures in Africa began to walk habitually on two legs.

They were flaking crude stone tools by 2.5 million years ago. Then some of them spread from Africa into Asia and Europe after two million years ago.

With somewhat less certainty, most scientists think that people who look like us -- anatomically modern Homo sapiens -- evolved by at least 130,000 years ago from ancestors who had remained in Africa. Their brain had reached today's size. They, too, moved out of Africa and eventually replaced nonmodern human species, notably the Neanderthals in Europe and parts of Asia, and Homo erectus, typified by Java Man and Peking Man fossils in the Far East.

But agreement breaks down completely on the question of when, where and how these anatomically modern humans began to manifest creative and symbolic thinking. That is, when did they become fully human in behavior as well as body? When, and where, was human culture born?

''It's the hot issue, and we all have different positions,'' said Dr. John E. Yellen, an archaeologist with the National Science Foundation.

For much of the last century, archaeologists thought that modern behavior flowered relatively recently, 40,000 years ago, and only after Homo sapiens had pushed into Europe. They based their theory of a ''creative explosion'' on evidence like the magnificent cave paintings in Lascaux and Chauvet.

But some rebellious researchers suspected that this theory was a relic of a time when their discipline was ruled by Eurocentrism. Archaeologists, the rebels contended, were simply not looking for earlier creativity in the right places.

Several recent discoveries in Africa and the Middle East are providing the first physical evidence to support an older, more gradual evolution of modern behavior, one not centered in Europe. But other scientists, beyond acknowledging a few early sparks in Africa, remain unswayed. One prominent researcher is putting forward a new hypothesis of genetic change to explain a more recent and abrupt appearance of creativity.