The Omo remains are a collection of hominid bones discovered between 1967 and 1974 at the Omo Kibish sites near the Omo River, in Omo National Park in south-western Ethiopia. The bones were recovered by a scientific team from the Kenya National Museums directed by Richard Leakey and others. The remains from Kamoya's Hominid Site (KHS) were called Omo 1 and those from Paul's Hominid Site (PHS) Omo 2.
Parts of the fossils are the earliest to have been classified by Richard Leakey as Homo sapiens. In 2004, the geologic layers around the fossils were dated, and the authors of the dating study concluded that the "preferred estimate of the age of the Kibish hominids is 195 ± 5 ka [thousand years ago]", which would make the fossils the oldest known Homo sapiens remains. In a 2005 article on the Omo remains, Nature magazine said that, because of the fossils' age, Ethiopia is the current choice for the "cradle of Homo sapiens".
The bones includes two partial skulls, four jaws, a legbone, around two hundred teeth and several other parts. The two specimens, Omo I and Omo II, differ in morphological traits. The Omo II fossils indicate more archaic traits. Studies of the postcranial remains of Omo I indicate an overall modern human morphology with some primitive features. The fossils were found in a layer of tuff, between a lower, older geologic layer dubbed Member I and a higher, newer layer dubbed Member III. The Omo I and Omo II hominid fossils are from similar stratigraphic levels over Member I.
Because very limited fauna and few stone artifacts were found at the sites when the original Omo remains were discovered, "the reliability of the dates and the provenance of the Kibish hominids" was "repeatedly questioned."
Dating and implications
About 30 years after the original finds, a detailed stratigraphic analysis of the area surrounding the fossils was carried out. This analysis argon-dated the Member I layer to 195,000 years ago and that of Member III to 105,000 years ago. The numerous new lithic records from Members I and III verify tool technology to the Middle Stone Age.
The lower layer (below the fossils) is considerably older than the 160,000-year-old Herto remains designated Homo sapiens idaltu, which were previously thought to have been the earliest humans. This suggests that, if humans did originate in Africa as is the current hypothesis, then they did not extend beyond there until much later than was previously thought. The rainy conditions at that time, which are known from isotopic ages on the Kibish Formation corresponding to the ages of Mediterranean sapropels, suggest increased flow of the Nile River and, therefore, increased flow of the Omo River. Climatic conditions after 185,000 years ago were too dry to allow speleothems to grow in the Levantine land-bridge inroad Eurasian migration. Recent African Origin theory suggests that H. sapiens sapiens evolved alongside other hominids for a considerable period of time before the other hominids became extinct.
- Fossil Reanalysis Pushes Back Origin of Homo sapiens. Scientific American 2005-02-17. Retrieved 2005-08-22.[Retrieved 2011-08-27]
- Fleagle, Jg; Assefa, Z; Brown, Fh; Shea, Jj (Sep 2008). "Paleoanthropology of the Kibish Formation, southern Ethiopia: Introduction". Journal of Human Evolution 55 (3): 360–365. doi:10.1016/j.jhevol.2008.05.007. ISSN 0047-2484. PMID 18617219.
- Mcdougall, Ian; Brown, FH; Fleagle, JG (2005). "Stratigraphic placement and age of modern humans from Kibish, Ethiopia". Nature 433 (7027): 733–736. Bibcode:2005Natur.433..733M. doi:10.1038/nature03258. PMID 15716951.
- Hopkin, Michael (2005-02-16). "Ethiopia is top choice for cradle of Homo sapiens". Nature News. doi:10.1038/news050214-10.
- Ian McDougall, Francis H Brown, John G Fleagle Sapropels and the age of hominins Omo I and II, Kibish, Ethiopia. Journal of Human Evolution (2008) Volume: 55, Issue: 3, Pages: 409-20PubMed: 18602675 Copyright © 2012 Mendeley Ltd. All rights reserved. doi:10.1016/j.jhevol.2008.05.012 [Retrieved 2012-01-02]
- Pearson, Om; Fleagle, Jg; Grine, Fe; Royer, Df (Sep 2008). "Further new hominin fossils from the Kibish Formation, southwestern Ethiopia". Journal of Human Evolution 55 (3): 444–7. doi:10.1016/j.jhevol.2008.05.013. ISSN 0047-2484. PMID 18691739.
- Vaks, Anton; Bar-Matthews, Miryam; Ayalon, Avner; Matthews, Alan; Halicz, Ludwik; Frumkin, Amos (2007). "Desert speleothems reveal climatic window for African exodus of early modern humans". Geology 35 (9): 831. doi:10.1130/G23794A.1.