Face, teeth features peg 300,000-year-old fossils as early humans, but brain shape yet to evolve
J.-J. HUBLIN/MPI-EVA, LEIPZIG
In a surprising and controversial geographic twist, the earliest known remains of the human species, Homo sapiens, have turned up in northwestern Africa, researchers claim.
Fossils attributed to H. sapiens and stone tools unearthed at Jebel Irhoud, Morocco, date to approximately 300,000 years ago, an international team of researchers report June 7 in two papers in Nature. Until now, the oldest human fossils came from East Africa and dated to around 195,000 years ago (SN: 2/26/05, p. 141). Although H. sapiens might have emerged in East Africa, some researchers also categorize a previously discovered fossil skull from South Africa, tentatively dated to about 260,000 years ago, as H. sapiens.
The Morocco fossils indicate that humankind’s emergence involved populations across much of Africa, and started about 100,000 years earlier than previously thought, says paleoanthropologist Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He led the research along with Abdelouahed Ben-Ncer of the National Institute of Archaeology and Heritage Sciences in Rabat, Morocco.
“Long before the out-of-Africa dispersal of Homo sapiens [70,000 to 60,000 years ago], there was a dispersal within Africa,” Hublin says. What’s now the Sahara was inhabitable around 300,000 years ago, so early forms of H. sapiens in northern African could have reached other parts of the continent and interacted with different H. sapiens groups, he suspects.
Excavations at Jebel Irhoud in the 1960s produced six Homo fossils, initially classified as Neandertals, as well as stone tools resembling those at European Neandertal sites. Researchers initially dated the remains to about 40,000 years ago. A 2007 report later estimated one fossil, a child’s jaw, was about 160,000 years old.
In one new paper, Hublin and colleagues describe 16 new fossils unearthed at Jebel Irhoud from 2004 to 2011. Remains of at least five individuals — three adults, an adolescent and a child — include a partial skull, a lower jaw, a partial upper jaw, six isolated teeth and several limb bones.
Using CT scans, researchers generated 3-D reconstructions of the Jebel Irhoud fossil skull and lower jaw. Hublin’s team compared measurements of these finds with those for Homo erectus, Neandertals and other Homo species from between around 1.8 million and 150,000 years ago, as well as H. sapiens fossils from the past 130,000 years.
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CT scans of fossils from a Moroccan site were used to produce composite reconstructions of a skull that some researchers attribute to the earliest known Homo sapiens. The skull displays a modern-looking face, left, combined with a braincase, right, shaped like those of older, now-extinct Homo species.
Facial characteristics of the Jebel Irhoud skull and teeth closely match those of people today, despite being larger, the scientists say. The Jebel Irhoud lower jaw also shares much in common with H. sapiens. All 22 Jebel Irhoud fossils qualify as H. sapiens, the scientists conclude.
Yet three Jebel Irhoud braincases — consisting of the new skull and two previously excavated, less complete specimens — are relatively long and low in height, compared with taller, rounded braincases typical of H. sapiens. Jebel Irhoud braincases more closely resemble those of earlier species, including H. erectus.
Facial and dental traits of H. sapiens were established by around 300,000 years ago, whereas brain shape has continued to evolve since then, the researchers propose.
Paleoanthropologist Erik Trinkaus of Washington University in St. Louis disagrees. Homo fossils dating to between around 600,000 and 200,000 years ago typically contain some features recalling older species and other traits foreshadowing later H. sapiens, Trinkaus says. Some of those fossils probably came from populations that were ancestors of people today. But that doesn’t mean those specimens, or the Moroccan finds, were H. sapiens, he contends. In fact, many of those Homo fossils have eluded consensus about their species identity.
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Along with fossils that might be the earliest examples of Homo sapiens, recent excavations in Morocco yielded sharp-edged stone tools that have often been considered typical of Neandertals.
In a second paper, Max Planck geoscientist Daniel Richter and colleagues date 14 stone artifacts found in and just above sediment that held the new fossil discoveries, allowing the researchers to narrow down the fossils’ age to approximately 300,000 years ago. Those artifacts, along with many of the 306 more excavated by Hublin’s team, showed signs of having been heated in the past. A dating technique can gauge the time since heating of rock or sediment occurred. In addition, new calculations of amounts of radioactive uranium in Jebel Irhoud sediment enabled dating the previously unearthed child’s jaw from the site to between around 350,000 and 220,000 years ago.
Most Jebel Irhoud stone tools were pounded off larger rocks that had been prepared by toolmakers. This technique appeared across much of Eurasia and Africa by around 300,000 years ago, among H. sapiens and Neandertals (SN: 4/4/15, p. 16), the researchers say.
J.-J. Hublin et al. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature. Published online June 7, 2017. doi:10.1038/nature22336.
D. Richter et al. The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age. Nature. Published online June 7, 2017. doi:10.1038/nature22335.