Study claims to have found oldest human fossils | Science News for Students

Study claims to have found oldest human fossils

They seem to expand the time our species is known to have been around by some 100,000 years
Jun 8, 2017 — 12:00 pm EST
old jaw

Fossils unearthed in Morocco from around 300,000-years ago, including this lower jaw, come from the oldest known Homo sapiens. Or that’s what some researchers now argue. Other scientists suspect the remains come from an earlier, related species.

 J.-J. HUBLIN/MPI-EVA, LEIPZIG

In a surprising and controversial twist, the earliest known remains of our species have turned up in northwest Africa, scientists report.

Fossils on Homo sapiens have been unearthed together with stone tools at Jebel Irhoud, Morocco. They date to some 300,000 years ago, an international team of scientists say. They offered their conclusions June 7 in two papers in Nature. 

Until now, the oldest human fossils came from much further south, in East Africa. Moreover, they dated to only around 195,000 years ago. That doesn’t rule out humans having evolved in East Africa. But puzzling fossils have turned up elsewhere, too. Some researchers claimed to have unearthed a H. sapiens skull in South Africa. It has been tentatively dated to about 260,000 years ago.

Humankind’s emergence involved populations across much of Africa, the Morocco fossils now suggest. And if the new fossils are truly from H. sapiens, then our species may have been around some 100,000 years longer than previously thought. That’s the conclusion of Jean-Jacques Hublin. He’s a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Hublin led the new Morocco research along with Abdelouahed Ben-Ncer. He comes from 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 now argues. What’s now the Sahara desert had been inhabitable roughly 300,000 years ago. So early humans in North Africa could have spread to other parts of the continent. There, they could have interacted with different H. sapiens groups, he suspects.

Excavations at Jebel Irhoud in the 1960s turned up six fossils of folk who belonged to species in the Homo genus. Initially these remains had been classified as Neandertals. Stone tools at the site did resemble those at European Neandertal sites. Initial dating suggested the fossils came from about 40,000 years ago. Later, in 2007, a report estimated one fossil from this site, a child’s jaw, was roughly 160,000 years old.

In one of the new papers, Hublin’s group describe 16 newer fossils from Jebel Irhoud. They had been discovered between 2004 and 2011. They included remains of at least five different individuals. Three of them had been adults, one had been a teen and the last a child. The fossils included a partial skull, a lower jaw, a partial upper jaw, six isolated teeth and several limb bones.

The researchers scanned some of the bones with X-rays, using a technology known as computerized axial tomography. From these scans, the scientists generated 3-D reconstructions of the fossil skull and lower jaw. Hublin’s team compared these bones to those from Neandertals, from Homo erectus and from other Homo species. All of these comparison fossils came from between around 1.8 million and 150,000 years ago. The scientists also included, for comparison, true human fossils that were 130,000 years old or less.

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 two skulls
X-ray scans of fossils from a Moroccan site were used to produce these reconstructions of a skull that some researchers attribute to the earliest known human. The skull displays a modern-looking face, left, combined with a braincase, right, shaped like those of older, now-extinct Homo species.
PHILIPP GUNZ/MPI-EVA, LEIPZIG

Facial traits of the Jebel Irhoud skull and teeth were larger than those of people today. Still, these bones and teeth closely match those of humans, the scientists say. Indeed, the Jebel Irhoud lower jaw also shares much in common with those of modern humans. All 22 Jebel Irhoud fossils qualify as H. sapiens, the scientists conclude.

Yet three braincases tell a different story. These include the newfound skull and two previously excavated, less complete specimens. Compared to braincases typical of humans, all of these are relatively long and low in height. In fact, the new braincases more closely resemble those of earlier species, such as H. erectus.

This would suggest that facial and dental traits of humans were established by around 300,000 years ago. Afterward, the brain’s shape continued to evolve, the researchers now propose.

Not everyone buys this argument. Among them is Erik Trinkaus. He’s a paleoanthropologist at Washington University in St. Louis. Homo fossils dating to between around 600,000 and 200,000 years ago typically contain some features recalling older species and other traits hinting at what would become H. sapiens, he says. Some of those fossils probably came from populations that were ancestors of modern humans. But that doesn’t mean those specimens — or the Moroccan finds — actually were humans, he contends. In fact, controversy simmers over the species identity of many fossils belonging to the Homo family tree.

In a second paper, Daniel Richter (another Max Planck scientist) and his colleagues date 14 stone artifacts. These come from in and just above the soils in which the new fossils were discovered. Knowing how old these were allowed the researchers to narrow down the Homo fossils’ age to approximately 300,000 years ago.

Another 306 artifacts have been excavated by Hublin’s team. Together, these showed signs of having been heated in the past. A dating technique can gauge the time since rock or soil has been heated. Other new measurements of radioactive uranium in the site’s soil enabled dating the previously unearthed child’s jaw from the site. It now appears to be between 350,000 and 220,000 years old.

Most Jebel Irhoud stone tools were pounded off of larger rocks that had been prepared by toolmakers. This technique appeared across much of Eurasia and Africa by around 300,000 years ago — among both humans and Neandertals, the researchers say.

stone tools
Along with fossils that might be the earliest examples of Homo sapiens, these sharp-edged stone tools have turned up at the site in Morocco.
MOHAMMED KAMAL/MPI-EVA, LEIPZIG

Power Words

(for more about Power Words, click here)

anthropology     The study of humankind. A social scientist who studies different societies and cultures is called an anthropologist.

archaeology     (also archeology) The study of human history and prehistory through the excavation of sites and the analysis of artifacts and other physical remains. Those remains can range from housing materials and cooking vessels to clothing and footprints. People who work in this field are known as archaeologists.

artifact     An object made by people.

braincase     A part of the skull that protects the brain.

colleague     Someone who works with another; a co-worker or team member.

computerized axial tomography     (CAT or CT, for short). A special kind of X-ray scanning technology that produces cross-sectional views of the inside of a bone or body.

continent     (in geology) The huge land masses that sit upon tectonic plates. In modern times, there are six established geologic continents: North America, South America, Eurasia, Africa, Australia and Antarctica. In 2017, scientists also made the case for yet another: Zealandia.

Eurasia     That part of the globe covered by Europe and Asia.

evolutionary     An adjective that refers to changes that occur within a species over time as it adapts to its environment. Such evolutionary changes usually reflect genetic variation and natural selection, which leave a new type of organism better suited for its environment than its ancestors. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.

evolve     (adj. evolving) To change gradually over generations, or a long period of time. In living organisms, the evolution usually involves random changes to genes that will then be passed along to an individual’s offspring. These can lead to new traits, such as altered coloration, new susceptibility to disease or protection from it, or different shaped features (such as legs, antennae, toes or internal organs).

excavation     The process of systematically removing earth from a site to uncover buried remains, such as bones or artifacts.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

genus     (plural: genera) A group of closely related species. For example, the genus Canis — which is Latin for “dog” — includes all domestic breeds of dog and their closest wild relatives, including wolves, coyotes, jackals and dingoes.

Homo     A genus of species that includes modern humans (Homo sapiens). All had large brains and used tools. This genus is believed to have first evolved in Africa and over time evolved and radiated throughout the rest of the world.

Homo erectus     An extinct species of hominid that lived in Africa and Eurasia between about 1.9 million and 70,000 years ago.

Neandertal     A species (Homo neanderthalensis) that lived in Europe and parts of Asia from about 200,000 years ago to roughly 28,000 years ago.

paleoanthropologist     A scientist who studies ancient humans and hominid biology, also the behavior and evolution of hominids evolved. This field is based on the analysis of fossils, remnants, artifacts or markings created or used by hominids.

population     (in biology) A group of individuals from the same species that lives in the same area.

radioactive     An adjective that describes unstable elements, such as certain forms (isotopes) of uranium and plutonium. Such elements are said to be unstable because their nucleus sheds energy that is carried away by photons and/or and often one or more subatomic particles. This emission of energy is by a process known as radioactive decay.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

tool     An object that a person or other animal makes or obtains and then uses to carry out some purpose such as reaching food, defending itself or grooming.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

uranium     The heaviest naturally occurring element known. It’s called element 92, which refers to the number of protons in its nucleus. Uranium atoms are radioactive, which means they decay into different atomic nuclei.

X-ray     A type of radiation analogous to gamma rays, but having somewhat lower energy.

Citation

Journal: J.-J. Hublin et al. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiensNature. Published online June 7, 2017. doi:10.1038/nature22336.

Journal: D. Richter et al. The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone AgeNature. Published online June 7, 2017. doi:10.1038/nature22335.