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Ancient fossils reveal earlier origins of modern humans

Led by Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology and Abdelouahed Ben-Ncer from the National Institute for Archaeology and Heritage in Morocco, an international research team has made groundbreaking discoveries at Jebel Irhoud, Morocco. Fossil bones of , along with stone tools and animal bones, were uncovered at this site, dating back around 300 thousand years. This finding represents the oldest securely dated fossil evidence of our species, predating previous discoveries by 100 thousand years. The results, published in two papers in the June 8th issue of Nature by Hublin and Richter, unveil a complex evolutionary history of Homo sapiens that likely spanned the entire African continent.

Both data from present-day humans and fossil remains consistently point to an African origin for Homo sapiens. Before these recent discoveries, the oldest securely dated Homo sapiens were known from Omo Kibish in Ethiopia, dating back to 195 thousand years ago, with a fossil from Herto, also in Ethiopia, dated to 160 thousand years ago. The prevailing belief was that all modern humans descended from a population in East Africa around 200 thousand years ago. However, the new data challenges this notion, revealing that Homo sapiens spread across the entire African continent approximately 300 thousand years ago.

Jean-Jacques Hublin emphasizes the shift in understanding, stating, “We used to think that there was a cradle of mankind 200 thousand years ago in East Africa, but our new data reveal that Homo sapiens spread across the entire African continent around 300 thousand years ago. Long before the out-of-Africa dispersal of Homo sapiens, there was dispersal within Africa.”

Jebel Irhoud, a well-known site since the 1960s, has provided human fossils and Middle Stone Age artifacts. The recent , starting in 2004, significantly increased the number of Homo sapiens fossils from six to 22. The fossils, including skulls, teeth, and long bones from at least five individuals, confirm Jebel Irhoud's importance as the oldest and richest African Middle Stone Age hominin site, shedding light on an early stage of our species.

To establish a precise chronology for these finds, researchers employed the thermoluminescence dating method on heated flints found in the same deposits. These flints indicated an age of approximately 300 thousand years ago, pushing back the origins of Homo sapiens by a significant one hundred thousand years.

Composite reconstruction of the earliest known Homo sapiens fossils from Jebel Irhoud (Morocco) based on micro computed tomographic scans of multiple original fossils. Dated to 300 thousand years ago these early Homo sapiens already have a modern-looking face that falls within the variation of humans living today. However, the archaic-looking virtual imprint of the braincase (blue) indicates that brain shape, and possibly brain function, evolved within the Homo sapiens lineage. Credit: Philipp Gunz, MPI EVA Leipzig

Geochronology expert Daniel Richter from the Max Planck Institute in Leipzig, now with Freiberg Instruments GmbH, emphasizes the rarity of well-dated sites of this age in Africa. The team's fortune lay in the fact that many flint artifacts at Jebel Irhoud had been heated in the past, allowing them to employ thermoluminescence dating methods on these artifacts. This facilitated the establishment of a consistent chronology for the newly discovered hominin fossils and the layers above them. The team also recalculated the direct age of the Jebel Irhoud 3 mandible from the 1960s, previously dated to 160 thousand years ago using a special electron spin resonance method. The new age, determined with state-of-the-art dating methods and conservative approaches, aligns with the thermoluminescence ages, revealing an older age than previously realized.

The mandible Irhoud 11 is the first, almost complete adult mandible discovered at the site of Jebel Irhoud. It is very robust and reminiscent of the smaller Tabun C2 mandible discovered in Israel in a much younger deposit. The bone morphology and the dentition display a of archaic and evolved features, clearly assigning it to the root of our own lineage. Credit: Jean-Jacques Hublin, MPI-EVA, Leipzig

The crania of modern humans exhibit distinct features that differentiate us from our fossil relatives: a small and gracile face and a globular braincase. The fossils from Jebel Irhoud, however, showcase a modern-looking face and teeth alongside a large but more archaic-looking braincase. Using advanced micro computed tomographic scans and statistical shape analysis, the team demonstrated that the facial shape of the Jebel Irhoud fossils closely resembles that of present-day modern humans. Despite this modern facial morphology, the Jebel Irhoud crania retain an elongated archaic shape of the braincase. Palaeoanthropologist Philipp Gunz from the Max Planck Institute for Evolutionary Anthropology explains that the inner shape of the braincase reflects the shape of the brain. The findings suggest that modern human facial morphology was established early in our species' history, while brain shape and potentially brain function evolved within the Homo sapiens lineage. Comparisons of DNA from and Denisovans with present-day humans reveal genetic differences related to brain and nervous system functions. Evolutionary changes in braincase shape are likely linked to genetic changes influencing brain connectivity, organization, and development that distinguish Homo sapiens from our extinct ancestors and relatives.

Virtual palaeoanthropology is able to correct distortions and fragmentations of fossil specimens. This reconstruction of the Irhoud 11 mandible allows its comparison with archaic hominins, such as Neandertals, as well as with early forms of anatomically modern Humans. Credit: Jean-Jacques Hublin, MPI-EVA Leipzig

The morphology and age of the fossils discovered at Jebel Irhoud not only provide crucial insights into the early of Homo sapiens but also support the interpretation of an enigmatic partial cranium from Florisbad, South Africa, as an early representative of our species. The evidence indicates that the earliest Homo sapiens fossils span the entire African continent, with significant discoveries at Jebel Irhoud, Morocco (300 thousand years), Florisbad, South Africa (260 thousand years), and Omo Kibish, Ethiopia (195 thousand years). This mosaic of findings suggests a complex evolutionary history of Homo sapiens, potentially involving the entirety of Africa.

Abdelouahed Ben-Ncer underscores the importance of North Africa in understanding the origins of our species, noting that the remarkable discoveries from Jebel Irhoud highlight the strong connections of the Maghreb with the rest of the African continent during the emergence of Homo sapiens.

The fossils at Jebel Irhoud were unearthed in deposits containing animal bones indicative of hunting activities, with gazelle being the most frequent species. The associated stone tools belong to the Middle Stone Age, showcasing Levallois prepared core techniques, and pointed forms are predominant. Notably, these tools were crafted from high-quality flint imported to the site. Absent from Jebel Irhoud are handaxes, commonly found in older sites, pointing to a distinctive Middle Stone Age assemblage that likely contributed to the adaptive success of Homo sapiens across the African continent.

Some of the Middle Stone Age stone tools from Jebel Irhoud (Morocco). Pointed forms such as a-i are common in the assemblage. Also characteristic are the Levellois prepared core flakes (j-k) Credit: Mohammed Kamal, MPI EVA Leipzig

Shannon McPherron, an archaeologist from the Max Planck Institute, emphasizes the similarities between the stone artifacts from Jebel Irhoud and those from contemporaneous deposits in East Africa and Southern Africa. This suggests that the technological innovations of the Middle Stone Age in Africa are interconnected with the emergence of Homo sapiens. The findings from Jebel Irhoud not only shed light on the evolution of our species but also challenge previous timelines, indicating that Homo sapiens evolved much earlier than previously thought. The widespread dispersal of Homo sapiens across Africa around 300 thousand years ago is attributed to changes in both biology and behavior, marking a significant chapter in our species' history.

Source: Max Planck Society

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