Jebel Irhoud (, Moroccan Arabic: ) or Adrar n Ighoud (), is an archaeological site in Morocco located just north of the town of Tlet Ighoud in Youssoufia Province, approximately south-east of the city of Safi.
It is noted for the hominin fossils that have been found there since the discovery of the site in 1961. Originally thought to be Neanderthals, the specimens have since been assigned to Homo sapiens and, as reported in 2017, have been dated to a "weighted average age" of 315,000 years ago. This makes the remains by far the earliest known examples of H. sapiens, and suggests that rather than arising in East Africa approximately 200,000 years ago, modern humans were present across the length of Africa 100,000 years earlier.
Site The site is the remnant of a solutional cave filled with of deposits from the Pleistocene era, located on the eastern side of a karstic outcrop of limestone at an elevation of . It was discovered in 1961 when the area was being mined for the mineral baryte. A miner discovered a skull in the wall of the cave, extracted it, and gave it to an engineer, who kept it as a souvenir for a time. Eventually, it was handed over to the University of Rabat, which organized a joint French-Moroccan expedition to the site that was headed by anthropologist Émile Ennouchi.
Excavation history Ennouchi and his team began their excavation of Jebel Irhoud in 1961. Before beginning excavation, Ennouchi's team removed 2000 tons of debris that covered the archaeological layers using low-level explosives. The excavation completed by Ennouchi's team used horizontal arbitrary 50 cm stratigraphic layers, or spits. Ennouchi's team identified the remains of approximately 30 species of mammals, some of which are associated with the Middle Pleistocene, but the stratigraphic provenance of these remains is unknown. During the Ennouchi excavations, two hominin fossils, Irhoud 2 and Irhoud 3, were discovered and identified as an adult and a child. The associated lithic technology was identified as Mousterian, leading the Irhoud hominins to initially be identified as Neanderthals. Ennouchi's team was also the first to attempt to date the site. They used radiocarbon dating, but their results revealed that the site was older than 50,000 years and was thus beyond the measurement capabilities of radiocarbon dating.
Another excavation was carried out by Jacques Tixier and Roger de Bayle des Hermens in 1967 and 1969, during which 22 layers were identified in the cave in search of more hominin fossils. Irhoud 4 and 5 were identified during these excavations and were the first human remains found within a known stratigraphic context at the site, and were found in association with the Levallois Mousterian tool industry.
Jean-Jacque Hublin conducted more recent excavations beginning in 2004.* "Here we report the ages, determined by thermoluminescence dating, of fire-heated flint artefacts obtained from new excavations at the Middle Stone Age site of Jebel Irhoud, Morocco, which are directly associated with newly discovered remains of H. sapiens8. A weighted average age places these Middle Stone Age artefacts and fossils at 315 ± 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 ± 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible."; These excavations continued the work of the 1960s excavations, performing a more detailed study of site stratigraphy and context. It was during these excavations that Irhoud 10 and Irhoud 11 were discovered, both of which were identified as adults. Recent work identifies the Jebel Irhoud individuals as early members of the H. sapiens clade.
Stratigraphy The site's stratigraphic layers were originally defined during the excavations in the late 1980s. Differently defined stratigraphic layers were identified during more recent research, this time using geological principles. A description of the more recent site stratigraphy is as follows: Layers 1-3 do not contain much archaeological material, layers 4-6 contain some archaeological material (lithic tools) and zooarchaeological remains (primarily Gazella species), Layer 7 contains sediment described as "cemented" and contains a higher density of archaeological materials (lithic tools, some burnt) and zooarchaeological remains (primarily bovids) than the upper layers and corresponds to layers where the first Jebel Irhoud fossils were found.
Geology Jebel Irhoud is a site with much geological diversity, including Triassic formations and Charkarkar cave, and Ganntour phosphate deposits. The current geomorphology of Jebel Irhoud was created during an event called the Hercynian orogeny. This event occurred between 310 and 280 Ma and created westward vergent folds. Three primary geological formation contributing to the Jebel Irhoud landscape: (1) Barite veins, (2) zones of barite or "substitution," and (3) karst deposits.
Dating Early work: morphology and lithic technology The skull finds were initially interpreted as Neanderthal by Ennouchi in his 1962 publication. Based on anatomical similarity with finds from Skhul, Omo, and Jebel Qafza, Santa Luca determined Jebel Irhoud 1 was not Neanderthal (published 1978).
The remains had archaic phenotypical features believed to be representative of the Neanderthals rather than H. sapiens. They were thought to be approximately 40,000 years old, but this was thrown into doubt by faunal evidence suggesting a Middle Pleistocene date (see: Faunal Remains and Environmental Context), approximately 160,000 years ago. Because of that, the fossils were reappraised as representing an archaic form of Homo sapiens or perhaps a population of Homo sapiens that had interbred with Neanderthals. This was consistent with the concept that the then-oldest-known remains of Homo sapiens, dated to approximately 195,000 years ago and found in Omo Kibish, Ethiopia, indicated an eastern African origin for humans at approximately 200,000 years ago. The Ethiopian Omo remains were more recently dated to about 233,000 years old.
Recent dating methods: thermoluminescence dating and burnt lithics Dating carried out by the Max Planck Institute for Evolutionary Anthropology in Leipzig revealed that the Jebel Irhoud site was far older than first thought. Fresh excavations carried out in 2004 by the Hublin team revealed more than 20 new bones from the remains of at least five individuals as well as a number of stone tools. The remains included part of a skull, a jawbone, teeth, and limb bones belonging to three adults; there were also those of a juvenile and a child aged about seven-and-a-half years old.
Some of the tools had been burned due to fires being lit on top of them, presumably after they had been discarded. Researchers used thermoluminescence dating to ascertain when the burning of these stone tools occurred and, by proxy, the age of the fossil bones that were found in the same deposit layer.
In 2017, the burnt tools were dated to approximately 315,000 years ago, indicating that the fossils are of approximately the same age. This conclusion was confirmed by recalculating the age of the Irhoud 3 mandible, which produced an age range compatible with that of the tools, at roughly 280,000 to 350,000 years old ( for the Irhoud 3 mandible, based on other fossils and the flint artefacts found nearby). These dates make the remains by far the earliest known examples of Homo sapiens.
This suggests that rather than arising in East Africa approximately 200,000 years ago, modern humans may have been present across the length of Africa 100,000 years earlier. According to study author Jean-Jacques Hublin, "The idea is that early Homo sapiens dispersed around the continent and elements of human modernity appeared in different places, and so different parts of Africa contributed to the emergence of what we call modern humans today." Early humans may have comprised a large, interbreeding population dispersed across Africa approximately 330,000 to 300,000 years ago. Thus, the rise of modern humans may have taken place on a continental scale rather than being confined to a particular corner of Africa.
Human remains
The site is most famous for its hominin fossils, and since its discovery, twenty-two hominin fossil remains have been found at Jebel Irhoud. When first discovered, they were interpreted as Neanderthal remains. Since then, they have also been suggested as being an early form of H. sapiens that interbred with Neanderthals, or they represented a different late-surviving archaic population in Africa. Recent research disputes these claims, concluding that the Jebel Irhoud hominin remains represent an early form of the H. sapiens clade, present during the Middle Pleistocene.
Ennouchi discovered a skull that he named Irhoud 1. It is now on display in the Rabat Archaeological Museum. The following year, he discovered part of another skull, designated Irhoud 2, and subsequently uncovered the lower mandible of a child, designated Irhoud 3. Tixier's excavation found a humerus designated Irhoud 4, and a hip bone recorded as Irhoud 5.
Further excavations were carried out by American researchers during the 1990s and then by a team led by Jean-Jacques Hublin starting in 2004. Hublin and colleagues recently discovered Irhoud 10 and 11, both of which were identified as adults and were integral in determining the species classification of the hominin remains. Hublin and colleagues have also provided the following table of hominin remains found at Jebel Irhoud. +Jebel Irhoud Specimen List SpecimensItem IDAnatomical PartYearStratigraphic PositionIrhoud 1No IDCranium1961Lower depositsIrhoud 2No IDCranium1962Lower depositsIrhoud 3No IDMandible (juvenile)1968Lower depositsIrhoud 4No IDHumerus (juvenile)1969Layer 18 of TixierIrhoud 5No IDCoxal (juvenile)1969Layer 18 of de Bayle des Hermens & TixierIrhoud 6No IDMandible fragment1961-69Identified among faunal remainsIrhoud 74766Lower right first premolar2004Initial cleaningIrhoud 84767Distal part of left lower molar2004Initial cleaningIrhoud 91653First or second lower molar2006Layer 4Irhoud 101678, 1679, 1680, 2178, 2259Cranium2007Layer 7Irhoud 114765, 3752Mandible2007Layer 7Irhoud 122196Lower incisor2007Layer 7Irhoud 132252Left proximal femur2007Layer 7Irhoud 142381, 2383Rib2009Layer 7Irhoud 152401Rib2009Layer 7Irhoud 162561, 2565Humerus (juvenile)2009Layer 7Irhoud 172670Right proximal femur2009Layer 7Irhoud 182838Lumbar vertebra2007Initial cleaningIrhoud 193747, 3748, 3749Fibula2009Layer 7Irhoud 203751Cervical vertebra2009Initial cleaningIrhoud 214200Maxilla2011Layer AIrhoud 224502, 4503Upper second and third right molars2011Layer A Hublin and his team also attempted unsuccessfully to obtain DNA samples from the hominin fossils, which would have provided necessary evidence towards the conclusion that these fossils are representative of the main lineage leading up to modern humanity and that Homo sapiens had dispersed and developed all across Africa. Because of the unclear boundaries between different species of the genus Homo, and the lack of genomic evidence from these fossils, some doubt the classification of these fossils as Homo sapiens.
Morphology The most important anatomical considerations when classifying the Jebel Irhoud remains are these specimens' facial/cranial, dental, and mandibular morphologies. Recent studies based on these morphological attributes have identified the Jebel Irhoud individuals as being closer aligned with modern human morphology than archaic hominin morphology, placing them within the early stages of the Homo sapiens clade.