for National Geographic News
Around 50,000 years ago, modern humans suddenly started leaving Africa. Over the course of the next 20,000 years, Homo sapiens pushed other hominid species to extinction and established populations in Australia, Asia, and Europe.
What spurred Homo sapiens to leave Africa after living there for at least 70,000 years? What made modern humans successful?
Archaeologists and anthropologists specializing in human origins tackled those questions this past weekend at the American Association for the Advancement of Science annual meeting held in Denver, Colorado. In a symposium titled Revolution and Evolution in Modern Human Origins: When, Where, and Why?, several differing perspectives were presented.
Defining the Debate
There is general agreement that Homo erectus, the precursor to modern humans, evolved in Africa and gradually expanded to Eurasia beginning about 1.7 million years ago. Anatomically modern humans—humans that more or less looked like us—arose in Africa at least 130,000 years ago.
By 100,000 years ago, several species of hominids populated the Earth. H. sapiens—us—lived in Africa, H. erectus in Southeast Asia and China, and Neandertals in Europe. Around 50,000 years ago, there was a sudden explosion of human migration out of Africa, and by about 30,000 years ago, we were the last ones standing.
What propelled modern humans out of Africa, and what gave us the edge over other species?
The debate is complicated by differing definitions of what constitutes "modern" behavior, and differing interpretations of the archaeological record.
Common elements used to define modern behavior include the ability to plan ahead; technological innovation, establishing social and trade networks; adapting to changing conditions and environments; and exhibiting symbolic behavior like cave painting, bead making (used to show status or group identity), or burying the dead.
The crux of the argument comes down to whether these abilities resulted from a sudden biological and genetic revolution, or a more gradual evolution of abilities that culminated around 50,000 years ago and propelled the exodus from Africa.
Evolution versus Revolution
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