About 200,000 years ago, a new human species branched off the Homo ergaster lineage in Africa—
Mitochondrial DNA shows that the initial human migration out of Africa followed three major pathways (FIGURE 11-35). One path turned west after leaving Africa and spread into Europe. A second path turned southeast and spread into southern Asia and through the Indo-
There was something about the world that those H. sapiens groups moved into as they left Africa that we would find bizarre—
Were two species of humans ever alive at the same time? If so, what happened?
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This is the situation that the first modern H. sapiens encountered when they left Africa. Neandertals (H. neanderthalensis) had already spread across Europe and the Middle East. Neandertals were about the same size as modern humans, but more robust and muscular. Fossils of Neandertals often include bones that had been broken and healed. These injuries provide two types of information about Neandertals.
The H. sapiens who migrated through the Indo-
In 2003, researchers discovered stone tools and fossils of a species of human only 3 feet (about 1 m) tall and with a brain volume of just over a pint (about 350 cc) on Flores Island, which lies east of Java. The paleontologists who discovered this species gave it the scientific name Homo floresiensis (“Flores man”), but the world press promptly called it the Hobbit because of its tiny size. When the dwarf human H. floresiensis lived, Flores Island was also home to a dwarf elephant, which H. floresiensis may have eaten, and a giant monitor lizard, which may have eaten H. floresiensis.
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After modern H. sapiens groups spread into the areas occupied by the three other human species, these three other species disappeared. Neandertals became extinct about 30,000 years ago, H. erectus about 27,000 years ago, and H. floresiensis about 12,000 years ago. Why did these three species vanish? We’re not sure. Previously, researchers thought that modern H. sapiens must have exterminated the other species, either by monopolizing access to food and living space or by killing them in battles for food and space. But recent results from DNA sequencing suggest that H. sapiens actually encountered and interbred with Neandertals, just as they emerged from Africa. This conclusion is based on the finding that at least 1% to 4% of the genetic makeup of most modern humans includes Neandertal DNA.
Now we are the only extant human species, a situation that is unique in the evolutionary history of humans. Ever since the first branching event, about four million years ago, multiple, closely related species of humans had coexisted. We are the first human species to be alone.
Modern humans (Homo sapiens) evolved in Africa about 200,000 years ago, and all living humans are descended from that evolutionary radiation. About 60,000 years ago, a small group of modern humans moved out of Africa, and the descendants of this group ultimately populated Europe, Asia, and the Americas. Three other species of humans were living at this time, all of which became extinct between 30,000 and 12,000 years ago, after modern humans had spread into the areas where they were living.
When modern humans left Africa to populate the other continents about 60,000 years ago, what other human species did they encounter, and how long did these other human species persist?
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