Chris Stringer: Meet the Relatives

Chris Stringer has a post in the Financial Times titled Meet the Relatives.  It is sort of a whirlwind tour through the evolution of the genus Homo.    He writes:

The discoveries of Homo floresiensis, Homo luzonensis, Denisovans and Homo naledi in the past 15 years remind us that the fossil record of humans is still very patchy — stone tools are scattered across much of Africa as a witness to widespread human occupation, yet fossil evidence has been recovered from less than 10 per cent of that continent’s area.

The percentage coverage for Asia is hardly any better: there is, for example, currently only one significant human fossil from the whole of the Indian subcontinent. The discoveries of the past few years underline just how much evolutionary history remains unknown, with other extinct lineages no doubt still to be revealed.

Many of the new finds challenge how we classify fossils in relation to Homo sapiens today. I continue to call the Neanderthals a different species from us, based on their distinctive skeletons and skulls; others feel that the recent evidence of interbreeding and increasing evidence of sophisticated behaviour mean that we should merge them, and the Denisovans, into our species.

I think that the discovery of the Xuchang hominins indicates that there has been considerable population mixing for several hundred thousand years.  As I wrote at the time:

These two Chinese skulls stand at the crossroads of these population movements. While showing clear Neandertal characteristics, they also express modern traits, possibly reflecting mixing with the late, modern human arrivals represented by the recent modern human finds at Daoxian. Yet they also express a clear link to ancient East Asian populations. The implications of these skulls are stark: there has been widespread population mixing and regional continuity in Europe and Asia for at least 400 thousand years. Not only did the Neandertals feel enough cultural kinship to mate and have children with these East Asian people, the early modern humans coming out of Africa did, as well. As Chris Davis of China Daily News put it: “One big happy family.”

Whether this represents such behavior at the peripheries of different species or that of one polytypic species is, as yet, unclear.  It is very clear that our understanding of how these populations interacted is rudimentary, at best. 

Large Denisovan Fossil Discovered

Nature News is reporting on a jaw fragment that has been discovered on the Tibetan Plateau that is close to 160,000 years old. From the story:

The research marks the first time an ancient human has been identified solely through the analysis of proteins. With no usable DNA, scientists examined proteins in the specimen’s teeth, raising hopes that more fossils could be identified even when DNA is not preserved...

Until now, everything scientists have learnt about Denisovans has come from a handful of teeth and bone fragments from Denisova Cave in Russia’s Altai Mountains. DNA from these remains revealed that the Denisovans were a sister group to Neanderthals, both descending from a population that split away from modern humans about 550,00–765,000 years ago. And at Denisova Cave, the two groups seem to have met and interbred: a bone fragment described last year belonged an ancient-human hybrid individual who had a Denisovan father and Neanderthal mother.

One of the most important aspects of the study is that it opens the door to answering questions of other fossils through protein analysis:

Previous research identified Neanderthal remains using both proteins and DNA — but the success of the latest study could lead to a greater emphasis on getting ancient proteins out of fossils that haven’t yielded DNA, says Chris Stringer, a palaeoanthropologist at the Natural History Museum in London. The method could prove particularly useful for older samples or those from southeast Asia and other warm climates, where DNA degrades quickest.

More Information From Denisova

Nature News is reporting about some more evidence from Denisova, following up on the bombshell news last year that bones discovered there belonged to a person (who they named “Denny”) who's father was a Denisovan and mother a Neandertal. From the story:

In the years that followed the discovery of Denisovans, scientists used DNA sequencing to attribute a few molar teeth from the cave to the same group4. They have also found other remains that harboured Neanderthal DNA. The analysis of Denny fills in some important details about the two groups. “We knew that Denisovans and Neanderthals had been there. We just didn’t think they interacted this intimately,” says [Svante] Pääbo. “It was so amazing to find direct proof — to find these people in the act, almost, of mixing.”

Denny’s discovery has also convinced Pääbo and other scientists that the remains of similar individuals, with recent ancestry from two groups of hominin, will be found — perhaps also in Denisova Cave. Researchers who analysed Denny’s genome found signs that the chromosome set that was contributed by her father, although clearly Denisovan, harboured some Neanderthal ancestry, which hints at earlier encounters between the groups2. “We should be able to pick up these individuals,” says [Katerina] Douka.

The Denisova cave appears to have been occupied for several hundred thousand years, being originally settled by either Denisovans or Neandertals, no one is sure which. Subsequent to this, it is unclear how much interbreeding actually occurred. 

“It’s still a head scratcher,” adds Tom Higham, an archaeological scientist at the University of Oxford, UK, who works with Douka and Brown. “It’s either an incredible piece of luck, or interbreeding happens so frequently that we might expect to find these types of occurrence in the archaeological record.”

One thing becomes increasingly clear with each new discovery, however: the complete replacement model of modern human origins, as espoused by Stringer and Andrews, is dead.

Daniel Everett: Homo erectus Could Speak and Make Boats

Bentley University Global Studies professor Daniel Everett argues that Homo erectus could speak and had the ability to make ocean-going vessels.  The Guardian has the story:

“Oceans were never a barrier to the travels of Erectus. He travelled all over the world, travelled to the island of Flores, across one of the greatest ocean currents in the world,” said Daniel Everett, professor of global studies at Bentley University, and author of How Language Began. “They sailed to the island of Crete and various other islands. It was intentional: they needed craft and they needed to take groups of twenty or so at least to get to those places.”

While Everett is not the first to raise the controversial possibility that H. erectus might have fashioned some sort of seagoing vessel, he believes that such capabilities mean that H. erectus must also have had another skill: language.

“Erectus needed language when they were sailing to the island of Flores. They couldn’t have simply caught a ride on a floating log because then they would have been washed out to sea when they hit the current,” said Everett, presenting his thesis at the meeting of the American Association for the Advancement of Science in Austin. “They needed to be able to paddle. And if they paddled they needed to be able to say ‘paddle there’ or ‘don’t paddle.’ You need communication with symbols not just grunts.”

It is pretty clear that Homo erectus hunted, at least in some fashion, could control fire and evidence seems to be accumulating that they hafted spears and, at least late in the range, the European variant set up rudimentary complex settlements.

There is, naturally, skepticism that any hominin form prior to Neandertals were sea-going: 

But others say that there is little evidence that H. erectus was a sophisticated seafarer, let alone had a language. “I don’t accept that, for example, [Homo] erectus must have had boats to get to Flores,” said Chris Stringer, head of human origins at the Natural History Museum in London. “Tsunamis could have moved early humans on rafts of vegetation.”

Before dismissing that idea out of hand, remember that it is the best one going to explain how the New World Monkeys got where they are, since Africa and South America had parted ways some 180 million years prior to their arrival.

I think there is likely not enough evidence to know one way or another if Homo erectus could sail the high seas and had speech, although the only skeletal evidence that we have for that part of the anatomy suggests not. 

How Will Climate Change Affect Human Evolution?

Gizmodo asked a number of scholars how they thought AGW will affect human evolution.  Some of the answers were interesting. Biological anthropologist John Hawks wrote:

I’ll be honest — the degree of climate change we are talking about in the next couple of centuries, which is on the order of several degrees Celsius, is by and large going to make the temperate regions of the world more similar in temperature to tropical Africa, where all our ancestors originated. We’re effectively terraforming the world to be more like our origins. The effects on humans are much more social and economic than evolutionary.

To the extent we see evolution, it will be changes in plant and animal species. Some will change the timing of their lives, some will invade new areas where they couldn’t adapt before, and many will become extinct — especially those today locked into small “reserves” that will undergo local climate shifts faster than they can adapt. And of course we will exert our own selection and genetic engineering upon our crops and domesticated animals to suit the changing climate.

Biological anthropologist Chris Stringer wrote:

The pace of change is likely to be too fast and dramatic for us to evolve physically to meet the challenges of a much warmer world. Any changes would have to come from cultural or social accommodation to the new situations – if that proves possible.

I think it is still way to early to tell how the earth will respond to anthropogenic changes in climate. If you will recall, only fifteen years ago, people were talking about global cooling.

Piltdown Back in the News

The study of palaeoanthropology has, over the course of its existence, two large mysteries: whatever became of the Peking Man remains, and who contrived the Piltdown hoax.  Now, it seems, there is a concerted effort afoot to divine the perpetrator of the Piltdown hoax once and for all.  Stephanie Pappas writes:

Writing in this week's issue of the journal Nature, Chris Stringer of the Natural History Museum, London, explains why he and his colleagues are still investigating a mystery that began 100 years ago.

"Personally, I am intrigued by the question of whether the hoax was driven by scientific ambition or by more jocular or vindictive motives," Stringer wrote. He and his colleagues plan to test the forged bones from the Piltdown case with modern methods, aiming to find out who most likely made them and why.

The Piltdown Hoax is one of the most successful scientific frauds in history. In December 1912, British paleontologist Arthur Smith Woodward and amateur antiquarian Charles Dawson announced to the world that they'd found an amazing early human fossil in Piltdown, England. The curious specimen had a humanlike skull with an apelike jaw. Given the scientific name Eoanthropus dawsoni, it was more commonly called Piltdown Man.

Over the last hundred years, suspicion has fallen primarily on Dawson, with other conspirators being implicated along the way, such as Arthur Keith, who saw others elected to the Royal Society before him and begrudged this, Sir Arthur Conan Doyle, who knew many of the conspirators and had his spiritualist religion ridiculed by Arthur Smith Woodward, the co-describer of the remains.  Suspicion even fell on the Jesuit priest, Teilhard de Chardin, who found some of the associated artifacts, himself.  Stephen Jay Gould thought that the priest had conspired with Dawson to concoct the skull.   It is also possible that a well-known palaeontologist and fossil expert at the time, Martin Hinton, may have been the perpetrator.  He had feuded with Smith Woodward for years and was also known as a practical joke-puller. 

John Walsh wrote probably the best treatise on the subject in which he squarely implicated Dawson, chronicling the fact that Dawson had been responsible for a string of hoaxes in the late 1800s and early 1900s, some of which were beginning to catch up with him when he died in untimely fashion in 1915.  It is fortunate that, by the time it was discovered to be a fake in 1953, most of the people involved had passed on. 

I think it will be hard to dislodge the general consensus that Dawson is the hoaxer but if he is not, I hope Chris and colleagues find who was.

Chris Stringer on Modern Human Origins

Chris Stringer was one of the original progenitors of the Out of Africa model of modern human origins, which posited that anatomically modern Homo sapiens arose in sub-Saharan Africa as a speciation event¹ and then replaced the archaic humans that they came into contact in other areas of the Old World. Needless to say, this perspective has been rocked by a number of astonishing studies that have come out in the last few years, including but not limited to these reports:

• Researchers say Neanderthals interbred with modern humans
• Shared Genes With Neanderthal Relatives: Modern East Asians Share Genetic Material With Prehistoric Denisovans
• Non-Africans Are Part Neanderthal, Genetic Research Shows
• A New Human Relative from the Siberian Mountains
• Skull suggests Stone Age humans interbred with more primitive relatives
• Ancient Humans Were Mixing It Up: Anatomically Modern Humans Interbred With More Archaic Hominin Forms While in Africa
  

These have cast considerable doubt on the integrity of anatomically modern humans as a separate species but suggest, instead that despite the timing of some of these trysts, Homo sapiens was a much more polytypic species then met the eye.

Now the grand don of the replacement model is undergoing a re-think. The Edge provides us with a wonderful trek through the history of the origins of modern humans debate and the current evidence for it. He hasn't given up the ship yet, though. He notes:

In my view the Neanderthals were closely related and probably potentially able to interbreed with modern humans, but until recently I considered that while there could have been interbreeding forty or fifty thousand years ago, it was on such a small scale that all trace of it vanished in the intervening years. But it now seems from Neanderthal genome studies that that was not so. We do have a bit of Neanderthal in us, you and I—it's a small amount, but certainly not negligible..

Does that mean Neanderthals are a different species or does it mean we should include them in Homo sapiens? Well, they are still only a small part of our makeup now, reflecting something like a 2.5% input of their DNA. Physically, however, they went extinct about 30,000 years ago. They had distinct behavior and they evolved under different conditions from us, so I still think it's useful to keep them as a separate species, even if we remember that that doesn't necessarily preclude interbreeding.

The percentage of Neandertal genes ranges from a low of 2% to a high of 9%, depending on who you read. The problem here is that, while we currently only have the small percentages, what can be said of the early modern Europeans, or of the people in Europe even as late as the Neolithic? It is almost certain that they would have had much higher percentages.

Further, do these genes explain the traits that Dave Frayer has been seeing for years in the earliest modern humans, such as the extended hemi-buns of the central European sample from Předmosti or archaic characteristics of the Mladeč crania?

The talk is quite long but worth every minute to get the full understanding of how vexing the search for the origins of modern humans has been. As Glenn Reynolds would say: Read the Whole Thing.

¹Stringer, C. B., & Andrews, P. (1988). Genetic and Fossil Evidence for the Origin of Modern Humans. Science, 239(4845), 1263-1268.
http://www.jstor.org/stable/1700885

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“Out-of-Africa Replacement Model”: Piling On

On the heels of the recent DNA arguments supporting hybridization between early modern Homo sapiens and archaic Homo sapiens in Africa comes fossil skeletal evidence.  As the Telegraph reports:

A study on human remains found in the Iwo Eleru cave in Nigeria, West Africa, shows that Stone Age humans in the area shared characteristics with much older human relatives. Palaeontologists leading the study believe their findings provide evidence that modern humans and older subspecies of human might have coexisted and even crossbred in Africa. The findings add weight to theories that ancient species of human lived alongside the anatomically modern humans after they first appeared in Africa 200,000 years ago.

Quoted in the article is Chris Stringer, one of the progenitors of the Out-of-Africa replacement model of modern human origins which was based on mitochondrial DNA studies done in the late 1980s.The article continues:

Professor Stringer said: "The majority view was that once modern humans emerged in Africa 150,000 years ago, it was kind of the end of the story and modern humans took over. "I think the reality is that the ancestral forms didn't just disappear but hung around alongside those that had evolved into modern humans. "Somewhere lurking in bits of Africa were these more archaic people and we are starting to get a picture of that."

I suspect that it is going to get very hard to pin down exactly where Homo sapiens starts. It is becoming more and more clear that anatomically modern Homo sapiens and archaic Homo sapiens went for the occasional “roll in the hay.” If so, as I pointed out earlier, there simply was no “speciation event.” This goes more to supporting the multiregional evolution model, as it applies to Africa, in which there was selection for more modern genes. This model may also apply to Europe, with the mixing of modern humans and archaic humans there. I suspect that this will spur reexamination of the early modern material from there, such as Mladeč, where the material dates from the Early Würm/Late Würm interglacial period.