Jan 26, 2018
This ancient jawbone suggests our species left Africa 40,000 years earlier than expected
In a collapsed cave on the western slope of Mount Carmel in Israel, researchers have found the jawbone of an ancient human who may have been one of the first modern members of our species to leave Africa. Here, in a huge cave by the Mediterranean Sea, ancient people roasted hare, turtle, and ostrich eggs and knapped stone tools from flint. If the researchers’ dates of 177,000 to 194,000 years for the jaw and tools hold up, it means that modern humans left Africa 40,000 years earlier than expected. The find may have implications for when and how our species arose, and how many waves of early humans left Africa.
Before now, the earliest modern human fossils outside Africa came from the nearby Skhul Cave on Mount Carmel and Qafzeh Cave in Israel sites dated to between 80,000 to 120,000 years old. But our species arose in Africa some 300,000 years ago, according to new dates on a skull in Morocco last year, and some researchers have claimed an early exodus from Africa based on fragmentary fossils and stone tools in the Middle East, Arabia, and China. But securely dated sites with accepted human fossils outside of Africa have been lacking.
The upper jaw was discovered in 2002 by students digging in the floor of Misliya Cave, the remains of a collapsed cave carved into the cliffs on the western slopes of Mount Carmel, 12 kilometers south of Haifa, Israel. From the first look at the upper jawbone, which retains a complete row of teeth on its left side, the researchers knew it was a member of our species, Homo sapiens. Its canine and other teeth resemble those of the modern humans at Skhul and Qafzeh, and it lacked features found in Neandertals.
The jawbone was excavated in the same sedimentary layer as thousands of “museum quality” handaxes and flint tools, says co-author Mina Evron of the University of Haifa. The tools were crafted with a sophisticated method called Levallois technology, which requires abstract thinking. Some researchers have suggested the method was invented by H. sapiens and may mark our species’ presence and early steps out of Africa.
Three teams independently dated the finds using uranium isotope decay and several luminescence methods, which determine how long ago mineral grains were last exposed to light. They dated the burned flint tools for about 179,000 years (plus or minus 48,000 years), which fits with other work dating Levallois style tools in Israel to 140,000 to 250,000 years ago. They also dated a sliver of enamel from a tooth to 174,000 years, and say that crust adhering to the upper jaw is at least 185,000 years old.
The dates on the tools seem solid, dating experts say. But several questions the dates on the fossil itself, partly because the authors write that the jawbone was scanned using computerized tomography three times, and the x-rays could have influenced the amount of radiation trapped in the tooth enamel, skewing the luminescence dates. Uranium dating expert Alistair Pike of the University of Southampton in the United Kingdom notes that a crust on the jawbone “is heavily contaminated by detritus.” The contamination could bias the radiometric dates on the crust, which includes a younger date of 70,000, says geochronologist Warren Sharp of the Berkeley Geochronology Center in California. He and others also note that relying on nearby tools is problematic because it’s possible that the bone was mixed into the tool-bearing layer later in time.
The team stoutly defends its dates, noting that its painstakingly controlled excavation links tools and fossil tightly in the same sedimentary layer and, thus, time.
If their dates are correct, “it’s mind-blowing,” says archaeologist Michael Petraglia of the Max Planck Institute for the Science of Human History in Jena, Germany, who says the find suggests that modern humans migrated out of Africa repeatedly, with multiple groups moving into the Middle East. They may have moved out of Africa when the climate was more humid 244,000 to 190,000 years ago, but gone extinct as the climate got arid again, says paleoanthropologist Marta Mirazon Lahr of the University of Cambridge in the United Kingdom, who was not involved with the new find.
The implications go back even further for co-author and physical anthropologist Israel Hershkovitz of Tel Aviv University in Israel, who says the find suggests our ancestors arose far earlier than thought. “[If] our species was in Israel 200,000 years ago, it suggests our species is very old—not just 300,000 years old, but older.”