Oldest Fossils of Our Species Push Back Origin of Modern Humans

The oldest known bones of our species, dating back around 300,000 years, have been discovered in a cave in Morocco.

The fossils — which belong to five individuals, including a teenager and a younger child — push back the origin of Homo sapiens by 100,000 years, scientists say. The fossils also suggest that our species originated throughout the entire African continent instead of mainly in its eastern corner as previous research had suggested.

The findings, described in two studies published in the June 8 issue of the journal Nature, represent the very roots of our species, the researchers said. As such, they help to clarify when and where Homo sapiens evolved from earlier lineages, such as Homo heidelbergensis or Homo rhodesiensis.

The five individuals may have been taking shelter in the Moroccan cave while hunting, possibly for gazelle or wildebeest, in what may have been a green Sahara. Though their faces looked a lot like ours do today, the individuals discovered in Morocco had smaller versions of a brain region called the cerebellum and an elongated braincase, the researchers said. [See Photos of the Fossilized Human Bones and Excavation Site]

Not Neanderthal

Archaeologists uncovered the human fossils, including a partial skull and a lower jaw, during excavations at the archaeological site of Jebel Irhoud in Morocco that began in 2004. But the site has a much earlier excavation history: Scientists first found some of the remains of these same individuals, along with stone tools, in the 1960s during mining operations. Those fossils were originally dated as about 40,000 years old and were considered to come from an African form of Neanderthal.

However, subsequent research cast doubts on whether those fossils were 40,000-year-old Neanderthal bones. For example, the excavations that collected the fossils did not make it clear which layers of earth the bones were found in, which makes their age uncertain, said Shannon McPherron, an archaeologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and a co-author of one of the new studies. [Image Gallery: Our Closest Human Ancestor]

In addition, before the 1980s, any human fossils that were about 40,000 years old and had primitive features, such as strong brow ridges, were often labeled as Neanderthal, whereas they might not be labeled that way today, said Jean-Jacques Hublin, a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology and co-lead author of one of the new studies.

The new analyses revealed that all of the fossils recovered from the site came from at least five individuals — three adults, one adolescent and one 7- to 8-year-old child, Hublin said. Those individuals date back about 285,000 to 350,000 years — much older than 40,000 years.

"These dates were a big 'wow,' I would say. We realized this site was much older than anyone could have imagined," Hublin told Live Science. "This material represents the very root of our species — the oldest specimens ever found in Africa or elsewhere."

They looked like us

In one study, computer models and hundreds of 3D X-ray measurements of the fossils suggested that numerous features of the face, jaw and teeth were almost indistinguishable from those of modern-day humans. Their faces were those "of people you could cross on the street today," Hublin told Live Science.

However, the braincase was rather elongated, resembling that of more archaic human lineages. Together, the anatomical features of these newly discovered fossils suggest "a rather more complex picture for the emergence of our species than previously thought, with different parts of the anatomy evolving at different rates — some fixed quite early in a modern way, and others taking a longer time to reach the modern condition," Hublin said.

Dating crystals

In the other new study, researchers analyzed flint tools found alongside the fossils. At one point in the distant past, these stone artifacts were heated by flame, perhaps when people there lit fires that inadvertently burned discarded flint tools scattered on or buried in the ground underneath, McPherron told Live Science.

Crystals within these artifacts gave off light when the researchers heated them, and the amount of light they gave off was related to how much time had passed since they were last heated. This analytical technique, known as thermoluminescence dating, suggested the site was about 300,000 to 350,000 years old.

"Well-dated sites of this age are exceptionally rare in Africa, but we were fortunate that so many of the Jebel Irhoud flint artifacts had been heated in the past," geochronology expert Daniel Richter, who was the lead author of the fossil-dating study when he was at the Max Planck Institute in Germany, said in a statement. (Richter is now at Freiberg Instruments GmbH.)

Moreover, Richter and his colleagues directly calculated the age of a human jawbone found at the site. Radioactive isotopes found within a tooth indicated that the jaw was as old as thermoluminescence dating suggested it was.

The scientists were not able to recover genetic data from these fossils because the heat and the age of the remains destroyed the DNA, Hublin said. Still, the elongated, primitive nature of the braincase revealed a number of facts about the biology of these ancient H. sapiens. For example, they had a smaller cerebellum — the brain region that helps coordinate muscle activity — than modern humans do, Hublin said.

Previous research suggested that a series of genetic mutations that play roles in brain development and the connection of different brain regions emerged in H. sapiens after the ancestors of modern humans split from extinct lineages such as the Neanderthals and the Denisovans, Hublin said. "This maybe explains the gradual changes in the braincase that we see that distinguish our lineage," he said. [Human Origins: How Hominids Evolved (Infographic)]

Animal fossils at the site also revealed that these ancient people ate plenty of gazelle meat, as well as the occasional zebra, wildebeest and other game, including perhaps ostrich eggs, said Teresa Steele, a paleoanthropologist at the University of California, Davis. Cuts and breaks on long bones suggest that humans broke them open, likely to eat the marrow, she added. Other animal fossils found at the site include ones from porcupines, aurochs, hares, leopards, hyenas, lions, foxes, jackals, snakes, tortoises, snails and freshwater mollusks.

"I think the overall picture we're looking at from the archaeological data is a hunting encampment, a place where people passing across the landscape took shelter at night as they moved through the area in search of subsistence," McPherron said.

Garden of Eden

Until now, the oldest H. sapiens fossils were found in eastern Africa, from the site of Omo Kibish in Ethiopia, suggesting that this was where our species originated. But now, these newfound 300,000-year-old fossils from northern Africa suggest that our species might not have evolved in a single area in Africa. Rather, these findings — in combination with a 260,000-year-old partial skull from Florisbad, South Africa, that a 1996 study suggested might have been from H. sapiens — reveal that our species might have evolved across all of Africa, the researchers said.

"If there is a Garden of Eden, it is Africa; it is the size of Africa," Hublin said. "Our model is one where there was probably the evolution of different populations of H. sapiens in different parts of Africa. Sometimes, there was some kind of isolation between them, but in other periods, they were connected when the environment changed — 'green Sahara' periods happened several times. During these periods of connection, we think there were exchanges of innovations, and also exchanges of genes."

One "green Sahara" period may have occurred between about 300,000 and 330,000 years ago, Hublin said. "This means grasslands over the Sahara. Rivers. Huge lakes, like those in Germany, in size. Fauna such as elephants and zebra. All over a geographic domain that is absolutely gigantic — the Sahara is the size of the United States," Hublin said. "These periods happened again and again, probably playing a role in what we think were episodes of connection and exchanges between different populations of H. sapiens."

Original article on Live Science.