There are several conflicting theories of how our species developed and spread around the world. One is the “out of Africa” theory which posits that our species evolved in Africa and spread from there to Asia and beyond. A competing theory, the multiregional model, claims that modern humans originated as a result of genetic contributions from hominin populations all around Europe, Asia, and Africa.
I’ve already posted on recent paleontological findings that cast some doubt on “out of Africa”. There’s more. The “out of Africa” theory predicts that human ancestors like H. erectus have shared habitats with and existed alongside our species. Evidence of such coexistence from a site in Indonesia where erectus had, apparently, persisted until as recently as 35,000 to 50,000 years ago was pointed to as confirming the hypothesis.
However:
The SoRT Project’s investigations occurred in Ngandong and Jigar, two sites in the “20-meter terrace” of the Solo River, Indonesia. The sediments in the terrace were formed by the flooding of the ancient river, but currently sit above the Solo River because the river has cut downward through time. The terrace has been a rich source for the discovery of Homo erectus and other animal fossils since the 1930s.
As recently as 1996, a research team dated these sites of hominin, or early human, fossils to as young as 35,000-50,000 years old. The analyses used a technique that dates teeth, and thus provided ages for several animals discovered at the sites. However, other scholars suggested the sites included a mixture of older hominins and younger animals, raising questions about the true age of the hominin remains.
The goal of the SoRT team, which included both members of the 1996 group and its critics, was to understand how the sites in the terrace formed, whether there was evidence for mixing of older and younger remains, and just how old the sites were.
Since 2004, team members have conducted analyses of animal remains, geological surveys, trenching, and archaeological excavations. The results from all of these provide no evidence for the mixing of older and younger remains. All the evidence suggests the sites represent just a short time period.
“The postmortem damage to the animal remains is consistent and suggests very little movement of the remains by water,” explained Briana Pobiner, the project’s archaeologist and a paleoanthropologist at the Smithsonian Institution’s National Museum of Natural History. “This means that it is unlikely that very old remains were mixed into younger ones.”
In addition, clues from the sediments exposed during excavation suggest to the projects’ geoarchaeologists, Rhonda Quinn, Chris Lepre, and Craig Feibel, of Seton Hall, Columbia, and Rutgers universities, that the deposits occurred over a short time period. The teeth found in different excavation layers at Jigar are also all nearly identical in age, supporting the conclusion that mixing across geological periods did not occur.
“Whatever the geological age of the sites is, the hominins, animals, and sediments at Ngandong and Jigar are all the same age,” said project co-leader Susan Antón.
The team applied two different dating techniques to the sites. Like earlier work, they used the techniques—U-series and Electron Spin Resonance, or ESR—that are applied to fossilized teeth. They also used a technique called argon-argon dating that is applied to volcanic minerals in the sediments. All three methods use radioactive decay in different ways to assess age and all yielded robust and methodologically valid results, but the ages were inconsistent with one another.
The argon-argon results yielded highly precise ages of about 550,000 years old on pumices—very light, porous volcanic products found at Ngandong and Jigar.
“Pumices are hard to rework without breaking them, and these ages are quite good, so this suggests that the hominins and fauna are this old as well,” said project geochronologist Carl Swisher of Rutgers University.
The finds in Indonesia may be as old as 550,000 years and as young as 143,000. This range is too ancient to demonstrate clear overlap with our species. The Indonesian erectus finds can no longer be pointed to as corroborative evidence that our species originated in Africa.
I understood that as they aged the homo erectus became homo cialis.
Sorry.
It’s not at all a “blow” to OOA, it’s actually more the opposite.
All we can say from this conclusion is that as sapiens spread out of Africa they never encountered H. erectus living around, at least not Indonesia. Just land not inhabited by another hominid. OOA is in its essence just that, sapiens evolved out-of-Africa instead of evolving simultaneously all around the world from erectus. It does not require that erectus was alive when sapiens arrived anywhere out of Africa. They could be, but it just not make any sense that they had to be. It actually weakens a bit the hypothesis as only then one could suggest regional continuity, without the complete extinction of erectus or any other human species previously inhabiting the region.
Just like what happened with the neanderthal in Europe. If neanderthals had been extinct long before sapiens arrieved, simply there would be no question about OOA. As they coexisted, one can’t immediately rule out the possibility that present-day Europeans evolved from neanderthals, instead of coming from a more recent migration out of Africa. This was ultimately ruled out, albeit some degree of mixing between neanderthals and sapiens occurred, or so it seems — to a degree that isn’t a “blow” against OOA as well, but it’s far “closer”, as at least there is the geographical continuity of a fraction of the Eurasians’ genes. In Indonesia, it’s nothing like that and only with utterly confusion one can argue that this result favors multirregionalism.
Indonesian erectus simply cannot be considered direct ancestors of Indonesian sapiens — which is what multirregionalism would posit — does not matter if there are morphological similarities in common, hinting a geographical continuity. It has to be regarded just a coincidence, as the Indonesian sapiens couldn’t possibly have evolved from those erectus, who were already dead when sapiens arrieved — coming from Africa.
Bad reporting (if not something to blame on the scientists themselves) combined with people that are for some reason eager to find some evidence against OOA.