The spread of humans

We come from a long line of failures. We are apes, a group that almost went extinct fifteen million years ago in competition with the better-designed monkeys. We are primates, a group that almost went extinct forty-five million years ago in competition with the better designed rodents. We are chordates, a phylum that survived in the Cambrian era 500 million years ago by the skin of its teeth in competition with the brilliantly successful arthropods. Our ecological success came against humbling odds.

 

The out of Africa hypothesis suggests all living humans evolved from a group that originated in Africa. It postulates that modern Homo sapiens spread out of Africa, into Europe and Asia, and replaced archaic Homo sapiens living in those regions. This hypothesis is supported by molecular data. In contrast, the multiregional hypothesis posits that the archaic Homo sapiens populations in the different regions (Europe, Asia, and Africa) all evolved together into modern Homo sapiens. While genetic changes would first occur in one locality, gene flow would spread those changes into the other localities.

 

Human history took off around 50,000 years ago, at the time of what is sometimes termed our Great Leap Forward. The earliest definite signs of that leap come from East African sites with standardized stone tools and the first preserved jewelry. Similar developments soon appeared in the Near East and in southeastern Europe, then (some 40,000 years ago) in southwestern Europe, where abundant artifacts are associated with fully modern skeletons of people.

 

The great leap forward coincides with the first proven major extension of human geographic range since our ancestors’ colonization of Eurasia. That extension consisted of the occupation of Australia and New Guinea, joined at that time into a single continent. Many archeological sites attest to human presence in Australia/New Guinea between 40,000 and 30,000 years ago. Within a short time of that initial peopling, humans had expanded over the whole continent and adapted to its diverse habitats, from the tropical rain forests and high mountains of New Guinea to the dry interior and wet southeastern corner of Australia.

 

With the settlement of Australia/New Guinea, humans occupied three of the five habitable continents (Eurasia is counted as a single continent). That left only two continents, North America and South America. The Americas were first settled around 11,000 B.C. and quickly filled up with people.