Iwo Eleru skull

The Iwo Eleru site is a large rock shelter in western Nigeria. The skull was found in 1965 by Thurstan Shaw and his team among over half a million Later Stone Age artefacts at the site.[3] It was found as part of a skeleton that was buried with a thin covering of soil. The skeleton was excavated and encased in plaster, and the skull was separated from the rest of the body.[3]

On the basis of charcoal remains that were found surrounding the skeleton, it was initially dated 9250 BC ± 200.[3] However, in a 2011 study conducted by Katerina Harvati, Chris Stringer and others, the dating of the remains was revised: with the help of uranium–thorium dating, a time span of 11.7–16.3 ka was suggested.[4]

The cranial vault is relatively long and low, and the frontal bone shows moderate recession. The brow ridges are moderately developed for a male and there is no pronounced nasal root. What remains of the nasal area suggest that the nasal bridge was relatively flat, and the evidence from X-rays points to little frontal sinus development.[5]

The upper face is missing except for a small collection of fragments. Parts of the maxillary-molar region have been identified (including the infraorbital foramen) and, based on what survives, it is unlikely that the upper face was large.[6] The mandible is well developed and has a masculine appearance, although there is no pronounced chin.[6] Apart from two lower premolars, the teeth are not attached to the jaws and it is uncertain where the surviving teeth were originally placed.[6] All the anterior teeth show noticeable attrition and most of the crown has been eroded by wear. Based on the evidence of tooth wear, the age of Iwo Eleru man has been estimated as over 30 years.[7]

What remains of the rest of the skeleton are generally crushed fragments of large bones.[8] The shafts of the humeri appear robust and the cortical bone is moderately thick. The shafts of the radius and femur are also robust.[9] The existing remains suggest he was of medium height and build, and was no taller than approximately 165cm.[10]

Don Brothwell and Thurstan Shaw said in 1971 that the sloping frontal vault was more pronounced in Iwo Eleru man than in both later Neolithic and recent sub-Saharan skull samples. However, they also found that the occipital structure, nasal root and the frontal bone of the skull "would qualify for identification as that of a proto-West African negro".[11]

In 1974 Chris Stringer said that there were surprising similarities between the crania of the much older Solo Man and Omo II with that of Iwo Eleru.[12] The 2011 study found that "Iwo Eleru possesses neurocranial morphology intermediate in shape between archaic hominins (Neanderthals and Homo erectus) and modern humans".[13] The authors of the study asserted that the dating of Iwo Eleru man to the late Pleistocene "implies that the transition to anatomical modernity in Africa was more complicated than previously thought, with late survival of “archaic” features and possibly deep population substructure in Africa during this time".[13]

It has been argued that Iwo Eleru man was an archaic hybrid or part of a relict archaic Homo population.[14][15][16] In 2014 Christopher Stojanowski of Arizona State University summarised the three dominant explanations for Iwo Eleru man's atypical cranial shape: the first, that Iwo Eleru was a hybrid with archaic African populations; the second, that Iwo Eleru man was a member of a relict archaic population that was replaced by more modern humans upon the onset of the Holocene era; and the third, that Iwo Eleru man was part of a population that diverged from the rest of North Africa's populations during a time of acute aridness in the Sahara desert that made it impassable until the arrival of the African humid period.[17]

In 2014 Peter J. Waddell of Massey University argued that Iwo Eleru man descended from a lineage 200–400 kya and whose extinction may have been caused by humans. Waddell also said: "Such a long apparently distinct lineage that terminated in West Africa perhaps 12kya, with no obvious sign of living descendants, suggests that the Iwo Eleru lineage quite probably represents a distinct species of near modern human. As such, the species name Homo iwoelerueensis suggests itself".[18][19] However, the University of Washington's Fred L. Bookstein cautions against naming Iwo Eleru man as a new species until more confirmatory evidence is discovered.[20]

• Asselar man

• Daniel Boettcher, 'Skull points to a more complex human evolution in Africa', BBC News.co.uk (16 September 2011).