Neanderthals may have died out earlier than before thought, researchers say.
These findings hint that Neanderthals did not coexist with modern humans as long as previously suggested, investigators added.
Modern humans once shared the planet with now-departed human lineages, including the Neanderthals, our closest known extinct relatives. However, there has been heated debate over just how much time and interaction, or interbreeding, Neanderthals had with modern humans.
To help solve the mystery, an international team of researchers investigated 215 bones previously excavated from 11 sites in southern Iberia, in an area known as Spain today. Neanderthals entered Europe before modern humans did, and prior research had suggested the last of the Neanderthals held out in southern Iberia until about 35,000 years ago, potentially sharing the region with modern humans for thousands of years.
Their data suggest that modern humans and Neanderthals may have actually lived in the area at completely different times, never crossing paths there at all. Even so, these findings do not call into question whether modern humans and Neanderthals once had sex — the findings simply indicate this interbreeding must have occurred earlier, before modern humans entered Europe.
"The genetic evidence for interbreeding — 1 to 4 percent Neanderthal DNA in present-day modern humans — suggests that interbreeding probably occurred before the period we are looking at in the Levant, the region around Israel and Syria, when modern humans first migrated out of Africa," researcher Rachel Wood, an archaeologist and radiocarbon specialist at Australian National University in Canberra, told LiveScience.
Scientists discover the ages of artifacts and fossils using a variety of techniques. For instance, radiocarbon dating determines the age of biological remains based on the ratio between the carbon isotopes (atoms of the same element with different numbers of neutrons) carbon-12 and carbon-14 it holds — this proportion changes as radioactive carbon-14 breaks down while stable carbon-12 does not. Researchers can also look at the layers of soil and rock in which objects are found — if these layers were not disturbed over the years, then objects in the same layer should be the same age.
The investigators concentrated on collagen, the part of bone most suited for radiocarbon dating. Only eight of these bones from two sites in Spain — Zafarraya Cave and Jarama VI — had enough collagen for analysis. (Image Gallery: Our Closest Human Ancestor)