F Rosa Rubicondior: Yet Another of Those Re-writes of Human Evolution?

Wednesday 25 October 2017

Yet Another of Those Re-writes of Human Evolution?

Left: upper left canine.
Right: upper right first molar
Credit: Mainz Natural History Museum
Prehistoric teeth fossils dating back 9.7 million years 'could rewrite human history' | The Independent

According to press reports, yet another re-write of human evolutionary history is due because a couple of 9.7 million year-old fossil teeth found in Germany look somewhat like those of "Lucy" (Australopithecus afarensis) from Ethiopia, Africa.

But things are maybe not what the headlines claim. Journalists have a vested interest in sensational headlines, even more so when the page carries adverts which are interspersed in the article itself and grab your attention. Also with a vested interest in sensational headlines, are those who supply the soundbites journalists yearn after.

"Paleontologists in Germany have discovered 9.7 million-year-old fossilised teeth that a German politician has hailed as potentially “rewriting" human history.

The dental remains were found by scientists sifting through gravel and sand in a former bed of the Rhine river near the town of Eppelsheim.

They resemble those belonging to “Lucy”, a 3.2 million-year-old skeleton of an extinct primate related to humans and found in Ethiopia.

However, they do not resemble those of any other species found in Europe or Asia.

Scientists were so confused by the find they held off from publishing their research for the past year, Deutsche Welle reports.

Herbert Lutz, director at the Mainz Natural History Museum and head of the research team, told local media: "They are clearly ape teeth. Their characteristics resemble African finds that are four to five million years younger than the fossils excavated in Eppelsheim.

“This is a tremendous stroke of luck, but also a great mystery."

At a press conference announcing the discovery, the mayor of Mainz suggested the find could force scientists to reassess the history of early humans.

So the person proclaiming the need for a re-write was the mayor of Mainz, Michael Ebling, who sensationally claimed "we shall have to start rewriting the history of mankind after today". Not a palaeoanthropologist but someone with a professional interest in putting Mainz on the map.

What the fuss is over are crowns of two teeth discovered in a alluvial deposits associated with the river Rhine in which many other fossils have been found. The molar is not especially remarkable but the canine bears some resemblance to those of hominins found in Africa, including the famous "Lucy", assumed by some to be the parent species of the Homo genus, or at least a cousin of our last pre-Homo species.

In September 2016, two teeth of an up to now undescribed member of the Hominoidea have been uncovered from sediments of the Proto-Rhine River near Eppelsheim, Germany, the type locality for the Eppelsheim Formation (i. e. Dinotheriensande) and of 25 mammals of various systematic positions. Together with other finds from Eppelsheim and the Wissberg location, which is only 18 km away, these are the northernmost occurrences of Miocene primates in Europe. Both teeth, the crowns of an upper left canine and an upper right first molar, are exceptionally well preserved and obviously come from the same body of unknown sex. Their sedimentological environment and the accompanying faunal elements point to an age shortly before the Mid-Vallesian crisis at ca. 9.7 Ma. While the molar shares characters with various other taxa, the canine reveals intriguingly potential hominin affinities: its lingual outline is clearly diamond-shaped; its ratio of lingual height / mesiodistal length is within the range of Australopithecus afarensis, Ardipithecus ramidus, Ardipithecus kadabba, and females of Pan troglodytes. The relative size of the canine, i. e. the ratio of the buccal heights of C and M1, is similar to those of e.g. Dryopithecus sp., Ankarapithecus meteai but also Ardipithecus ramidus. Both, reduced size and shape of the canine likely indicate that the new species from Eppelsheim had lost a honing (C/p3) complex already ca. 9.7 Ma ago. From all information gathered up to now, the question arises, if the newly discovered Eppelsheim species may be related to members of the African hominin tribe.

I suspect something was lost in translation from the original German.

The basis for the claim that the teeth 'obviously came from the same body' appears to be that they were found just 60 cm apart in the same sand layer. Dating was based on a third fossil found in the same layer of a species [of horse] known not to have evolved until 11.1 million years ago.

With such tenuous evidence, and with so much evidence to the contrary, it is hardly surprising that the extraordinary conclusion that hominins may have evolved in Eurasia and migrated into Africa is by no mans universally accepted. Extraordinary claims require extraordinary evidence, and this just doesn't meet that requirement.

Michael Greshko, writing in National Geographic, for example, weighs in with:


Based on what Lutz's team has published, however, outside experts say that the teeth hardly “force us to reexamine the theory that humans originated from Africa,” as ResearchGate’s interview with Lutz attests.

For one, we must be careful not to confuse modern humans with hominins, the bigger lineage containing humans and our closest extinct relatives, or hominoids, the even bigger group containing hominins, chimpanzees, gorillas, and other apes.

Overwhelming fossil and genetic evidence points to an African origin for modern humans, who left Africa no earlier than 120,000 years ago and most likely between 50,000 and 80,000 years ago. The Eppelsheim teeth are roughly a hundred times older. If the Eppelsheim teeth say anything about human evolution, they help to clarify where and how the earliest hominoids lived and evolved.

But some experts in the field question if the teeth really belong to a hominoid.

The canine tooth described in the paper has an unusual, intriguing shape, says University of Toronto paleoanthropologist Bence Viola, an expert on the teeth of humans' extinct relatives. However, the molar—which he says is the more important tooth for classification purposes—contradicts any case for a human connection.

“I think this is much ado about nothing,” he says by email. “The second tooth (the molar), which they say clearly comes from the same individual, is absolutely not a hominin, [and] I would say also not a hominoid.”

Instead, most experts we contacted say that the molar probably belongs to a species of pliopithecoid, an extinct, primitive branch of primates that lived in Europe and Asia between roughly seven and 17 million years ago.

Greshko goes on the point out that the Pliopithecoids are very distant relatives of humans. Some authorities believe they split from the common ancestor of Old World monkeys and the anthropoid apes before the latter diverged, so the teeth this species came from could be more distantly related to humans than humans are to baboons. The team even acknowledge in their paper that the molar resembles that of a Pliopithecoid, Anapithecus, known from a jaw-bone dug up in Hungary.

But David Begun, a paleoanthropologist at the University of Toronto is equally dismissive. Gresko quotes him as saying, (by email):

The 'canine' looks to me like a piece of a ruminant tooth. It has a funny break that makes it look a bit like a canine, but it is definitely not a canine, nor is it [from] a primate.

What is maybe the most surprising thing about this reports is that it is only interim and there are other plausible explanations. The authors themselves told ResearchGate:

RG: Do you have any ideas as to how this could happen?

It’s possible that, with the morphology of this canine tooth being so similar to more recent examples from Africa, the species could be related. That would mean that a group of primates was in Europe before they were in Africa.

There’s also the phenomenon of convergence, when evolutionary pressure causes the same characteristic to develop in multiple locations. Now the questions is whether it’s possible that’s what happened. There are few thousand kilometers between the species in East Africa and here in Central Europe, and millions of years. Is it possible that this uncannily similar characteristic developed two times, completely independently of one another. So here we are, perplexed. We want to collaborate with other researchers to process these finds, and hopefully in one or two years, we’ll know a lot more about what we’ve got on our hands. It’s definitely a fantastic, exciting story.

RG: What are the next steps?

Lutz: We’ll get in touch with our colleagues, who are just as surprised and dumbfounded as we are right now. We want to bring in specialists in particular investigative methods. The preservation of the crown of the tooth and it’s enamel is absolutely outstanding. These teeth are as well preserved as if I’d ripped them out yesterday. So we can use high-resolution x-rays to examine the inner structure of the enamel. That can give you information about the individual’s age and the development of this particular animal, things like stunted growth. It’s similar to tree rings. Another colleague of mine is focusing on wear on the chewing surface. There are tiny scratches and indentations, and there are areas where the tooth is chewed up. From all of this, you can draw conclusions about diet. These are all investigations that can be done really well with these samples, but we’re just getting started with all that.

So, let's wait to see what these specialist colleagues have to say before the re-writes detailing how humans evolved in Mainz begin, and before the crowds begin flocking to the Mainz Natural History Museum to see the earliest hominid remains on display.

Apropos of nothing in particular, I'm not sure who does the biggest disservice to science; the journalists who sensationalise discoveries to the point of misleading the public, who later discover that the finds were not what they were led to believe, or even, like creationists, take comfort from the impression that 'science got it wrong again!', or the scientists who pander to the need for 'sensation' in the popular press.

Yes, of course the textbooks need to be reviewed and revised to update them with the latest discoveries but this does not mean the earlier versions were wrong so much as simply incomplete. Only very rarely does a single find overturn an entire body of evidence and require a complete re-write. How, for instance, could a couple of teeth, tentatively and superficially resembling early hominid teeth from Africa, ever overturn the vast amount of evidence that the hominin branch of the evolutionary tree evolved in Africa?

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