The Omo remains are a collection of hominin—formerly named hominid (see below)—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 I and those from Paul's Hominid Site (PHS) Omo II.
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 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. Because this discovery is the earliest thus far, Ethiopia is the current choice for the cradle of Homo sapiens".
This article contains competing terms (hominin and hominid) for naming the collected species of Homo and Homo's closest relatives and ancestors after splitting from the chimpanzees. The conflict is explained, re the use of modern hominin, here: (the Hominini as hominins), and versus the original usage of hominid, here: (cf. Several revisions over time: hominid and hominin). (In this article, hominid is italicized when the traditional term is intended—or is necessary, as in a quotation, or in a record, etc.)
The bones include 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 named Member I and a higher, newer layer dubbed Member III. The Omo I and Omo II hominin fossils were taken 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 done. The Member I layer was argon-dated to 195,000 years ago and the (higher layer) Member III to 105,000 years ago. Numerous recent lithic records verify the tool technology from Members I and III to the Middle Stone Age.
The lower layer, Member I, (below the fossils) is considerably older than the 160,000-year-old Herto remains designated as Homo sapiens idaltu. 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. But the climates changed such that after 185,000 years ago conditions were so dry as to not allow speleothems to grow in the caverns in the Levantine land-bridge region, the vital inroad for Eurasian migration from Africa. The Recent African Origin theory suggests that H. sapiens sapiens evolved in Africa and migrated from there to the rest of the world, most recently some 70,000 years ago.
Archaic Homo sapiens, as from the Omo remains, progressed to H. s. idaltu, which were anatomically modern but not so behaviorally; then to H. s. sapiens, who are the anatomically and behaviorally modern humans of today. Recent DNA evidence shows there was little gene flow from previous hominins such as Neanderthal and Denisovan.
- 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" (PDF). Geology 35 (9): 831. doi:10.1130/G23794A.1.