I’ve been baffled by the spread of a non-story over the past couple days, about the supposed discovery of the oldest fossil of our species, doubling the age of our species from 200,000 years to 400,000 years and overturning the generally-accepted idea that Homo sapiens evolved in Africa.
Here’s a typical report, from the Associated Press:
Researchers: Ancient human remains found in Israel
JERUSALEM—Israeli archaeologists said Monday they may have found the earliest evidence yet for the existence of modern man, and if so, it could upset theories of the origin of humans.
The hook for this story is the publication of a paper in the American Journal of Physical Anthropology. Did the reporters who hyped this story actually look at the paper itself? I have to wonder.
Let me quote a few pieces from it. You tell me where the scientists actually claim they have identified 400,000 year fossil of Homo sapiens.
Here is the abstract (I’ll define a few terms and give context afterwards):
This study presents a description and comparative analysis of Middle Pleistocene permanent and deciduous teeth from the site of Qesem Cave (Israel). All of the human fossils are assigned to the Acheulo-Yabrudian Cultural Complex (AYCC) of the late Lower Paleolithic. The Middle Pleistocene age of the Qesem teeth (400–200 ka) places them chronologically earlier than the bulk of fossil hominin specimens previously known from southwest Asia. Three permanent mandibular teeth (C1-P4) were found in close proximity in the lower part of the stratigraphic sequence. The small metric dimensions of the crowns indicate a considerable degree of dental reduction although the roots are long and robust. In contrast, three isolated permanent maxillary teeth (I2, C1, and M3) and two isolated deciduous teeth that were found within the upper part of the sequence are much larger and show some plesiomorphous traits similar to those of the Skhul/Qafzeh specimens. Although none of the Qesem teeth shows a suite of Neanderthal characters, a few traits may suggest some affinities with members of the Neanderthal evolutionary lineage. However, the balance of the evidence suggests a closer similarity with the Skhul/Qafzeh dental material, although many of these resemblances likely represent plesiomorphous features.
These teeth are from a site that’s between 400,000 and 200,000 years old in Israel called the Qesem Cave. Archaeologists have been working at the site for years now, bringing forth tools that some kind of hominin was using to cut up meat. Now researchers have found a few teeth from the site, in the older layers.
Hominins–that is, species closer to us than to chimpanzees–left fossils during this period all over the Old World, from South Africa to England to Java. They all clearly belong to our own genus, Homo. They share a number of key traits, including big brains, small teeth, and many other subtler but more diagnostic traits. But which species of Homo do they belong to? Here’s where things get tricky. A lot of fossils in East Asia are similar enough to one another that they’re considered one species, called Homo erectus. But some fossils from China from this age don’t fall so neatly into this group. Are they another species? Are they just an odd subspecies of H. erectus? A firm answer is hard to find.
Over in Europe, hominins first arrived 1.2 million years ago. At 400,000 years ago, the fossil record in Europe includes a species known as Homo heidelbergensis. Among other things, it is the first species known to make wooden spears. Some fossils from Asia and Africa resemble H. heidelbergensis, too.
Now, let’s turn the clock forward on each continent…
In Europe, the H. heidelbergensis fossils start to look a lot like Neanderthals. By about 200,000 years ago, the fossil record in Europe contains full-blown Neanderthals.
In Asia, H. erectus holds on 200,000 years ago, although there are other fossils that look like they might belong to H. heidelbergensis.
In Africa, H. heidelbergensis and other hominins give way to the first full-blown Homo sapiens fossils. These are fossils that have a number of different traits that link them clearly to us, and distinguish them from other hominins. (Here are details on two important ones: Omo and Idaltu)
There were probably other lineages of hominins living at the same time as well–such as the Denisovans of East Asia.
What about the region around Israel, where the new teeth come from?
The fossil record offers a picture of hominins evolving in Africa, and pulses of new lineages rolling out through Israel and neighboring regions, and then onward to Europe and Asia. Some 1.4 million years ago, for example, a species of early Homo left fossils in Israel at a site called Ubeidiya. At several sites in and around Israel, paleoanthropologists have found fossils and tools dating back 400,000 to 200,000 years ago–the same period as the Qesem site. Unfortunately, the fossils are mostly fragments that might belong to a number of different species. The tools are equally ambiguous.
Something really interesting happened later in Israel, between about 130,000 and 50,000 years ago. It appears that Homo sapiens, having evolved in Africa, expanded tentatively into the Near East for the first time. Fossils of tall, slender Homo sapiens turn up at a site called Skhul/Qafzeh. But then they vanish, replaced for tens of thousands of years by Neanderthals. Only later does Homo sapiens expand again out of Africa, and this time they don’t retreat. Instead, it’s the Neanderthals that disappear from the Near East, dwindling away to refuges such as Spain before becoming extinct.
The new paper documents the struggle of the scientists to figure out who the Qesem teeth belong to. In some ways, they seem more like Neanderthal teeth. In others, they seem more like the choppers of Homo sapiens, as represented by the Skhul/Qafzeh fossils. The authors tilt towards a relationship with Homo sapiens, but mostly because the teeth are “plesiomorphous.” That term refers to a trait that was already present before the origin of a group of species. It does not refer to a trait that closely links all individuals who have it into a single lineage.
Here’s a simple example of what plesiomorphous means. Let’s say you find a fossil at a site where you had already found dogs and birds. The new fossil has four legs. In that respect, it’s more like a dog than a bird.
But it would not make sense for you to conclude that the fossil was a dog. The common ancestor of dogs and birds had four legs, and birds evolved into two-legged animals. But alligators have four legs, too, and they’re closer to birds than to dogs. All those four legs really tell you is that the fossil isn’t a bird.
The Qesem teeth–in some respects–lack distinctive Neanderthal features. Perhaps they are human. Or perhaps they belong to some other hominin, like a Denisovan.
Here’s how the scientists end their paper:
There are three scenarios that might account for the morphological details in the Qesem teeth. The first one is of a local archaic Homo population occupying southwest Asia during the Middle Pleistocene, to which the Qesem specimens would be attributed. Perhaps relevant in this regard, the Qesem lithic assemblages studied to date indicate a local origin, with no evidence of African and or European cultural affinities (Barkai et al., 2005; Gopher et al., 2005; Barkai et al., 2009). Albeit the lack of other diagnostic Middle Pleistocene SW Asian teeth, considering the evidence in its entirety, we believe that the Qesem ‘‘package’’ is more Skhul/Qafzeh like, even if some of its features are plesiomorphous.
The second scenario is one of long-term in situ evolution of Neanderthals in southwest Asia. The presence of shoveling and a lingual tubercle in the stratigraphically younger maxillary teeth may be indicating the emergence of the Neanderthal morphological pattern during the Middle Pleistocene in southwest Asia. This would parallel the situation documented in Europe, where the Neanderthal evolutionary lineage has been shown to have roots extending deep into the Middle Pleistocene (Arsuaga et al., 1997; Stringer and Hublin, 1999; Bischoff et al., 2007). Under this scenario, southwest Asia would represent one regional subpopulation within the wider geographic range of the evolving Neanderthal lineage. Nonetheless, the large and well dated samples of fossil humans from Skhul/Qafzeh that post-date the Qesem specimens but predate most of the Neanderthal specimens from the region do not show an accentuation of Neanderthal features.
The third scenario is that more than one Pleistocene human taxon is represented within the Qesem dental sample. The mandibular teeth are stratigraphically deeper (older) but are smaller and lack plesiomorphous features identified in the chronologically later specimens. The differences between these chronologically disparate samples may reflect a population or species level distinction, and may involve population replacement on a local scale.
Resolution of these alternative scenarios must await further discoveries of additional and more complete Middle Pleistocene remains from southwest Asia. Nevertheless, the Qesem specimens represent an important contribution to the growing sample of Pleistocene human fossils from this circum-Mediterranean region of the Old World.
Nowhere in this conclusion do the authors say that these teeth belong to Homo sapiens. Nowhere do they say they have just doubled the age of our species. Nowhere do they say that our species evolved in the Near East, not in Africa. There are only some vague hints that the teeth might be “Skhul/Qafzeh-like.” Or they might be something else.
While the paper itself is non-commital in its conclusions, it contains lots of good detail about the teeth, which is why it probably got accepted at the American Journal of Physical Anthropology. Who knows how some reporter got the idea that scientists had discovered the oldest fossils of Homo sapiens? It does seem that one of the authors has played footsie with reporters, offering some tasty quote-bait:
“It’s very exciting to come to this conclusion,” said archaeologist Avi Gopher, whose team examined the teeth with X-rays and CT scans and dated them according to the layers of earth where they were found.
He stressed that further research is needed to solidify the claim. If it does, he says, “this changes the whole picture of evolution.”
The logical thing a reporter should then do is ask, “How exciting can this conclusion be, when you never actually made it in the paper?”
The illogical thing to do is to declare that these teeth could “rewrite the evolutionary history of our species.”
[Image: AP Photo/Oded Balilty]
[Update: Brian Switek scoffs at Wired.]
[Update 12/31: Nature News interviewed Ari Gopher, the lead author on the paper, about the hype (and the take-downs from me and Switek). The article is particularly useful for finally tracking down the source of all these articles: a press release from Tel Aviv University that claims that "evidence was discovered pointing to the existence of modern man (Homo sapiens) in Israel as early as 400,000 years ago." (The press release was only in Hebrew, so I'm relying on Nature's translation.) Gopher claims that he told all the reporters who called him to be very cautious, but didn't think the press release was incorrect. "We offer the most reasonable conclusion based on the statistical evidence: that they represent the same population as the Skhul and Qafzeh finds, thus pushing the date for that type of early man back to a much earlier time."
Is it me, or is he talking about some other paper I haven't seen yet?]
Links to this Post
- Ciencia Kanija » ¿El fósil de Homo Sapiens más antiguo? Venta de humo periodística | December 29, 2010
- Quick Links | A Blog Around The Clock | December 29, 2010
- Will a new discovery rewrite human evolution? at Skeptical Science | January 1, 2011
- Four Stone Hearth: Volume 110 « Afarensis: Anthropology, Evolution, and Science | January 5, 2011
- Modern insanın evrimsel tarihi değişemez!* « Naturalis Histeria | January 5, 2011
- Denti umani di 400.000 anni fa?/2 « Il Fatto Storico | January 6, 2011
- 400,000 Year Old Human Teeth? « Life « Science Today: Beyond the Headlines | January 6, 2011
- Evidence of early man found in Israel - Page 4 - Religious Education Forum | January 10, 2011
- Evolution: ask your questions here - Page 2 - Religious Education Forum | January 15, 2011