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john hawks weblog

paleoanthropology, genetics and evolution

Photo Credit: Pre-Clovis Gault Assemblage artifacts. Thomas Williams et al. (2018) CC-BY-NC

ZooMS finds more Denisovans

A nice news article in Nature about the “zooarchaeology by mass spectrometry”, or ZooMS work being done at Denisova Cave by Katerina Douka and coworkers: “Denisovan hybrid cave yields four more hominin bones”.

This approach uses the slight variations in amino acid sequence of the collagen protein to identify the mammal species represented by a small sample of bone. Within many archaeological sites, the average bone fragment is an unidentifiable piece of bone shaft that even the most skilled anatomist is unlikely to identify to species. That means the “faunal collection” of the average Paleolithic archaeological site may contain hominin pieces that cannot be identified.

Excavation at Denisova Cave, credit John Hawks CC-BY-NC-ND
Excavation at Denisova Cave, credit John Hawks CC-BY-NC-ND

The ZooMS technique allows a basic identification of a bone specimen to biological family or in some cases species. It relies upon differences in the amino acid sequence of the collagen protein in different animals.

Archaeologists can use this information on bone fragments to add resolution about prey species exploited at a site. Being able to quantify bovid, cervid, or equid from fragments might help show which species hyenas were bringing into a site, and which the hominins were hunting. But the most newsworthy use of the method has been to find hominin fragments, which then can be moved into a queue for ancient DNA sampling.

ZooMS was how Samantha Brown and coworkers identified the Denisova 11 specimen, whose DNA sequence was reported earlier this year. The Vindija 33.16 specimen originally targeted for sequencing by Pääbo’s research group was not found using collagen chemistry, but it had a similar history: a barely-identifiable bone fragment, it was assigned to the faunal collection and later identified by an anthropologist as hominin.

This week’s story, reporting on a conference presentation by Brown at the European Society for Human Evolution, is that the Denisova ZooMS sampling has uncovered an additional four hominin fragments. The work goes on, systematically going through thousands of bone fragments:

Meanwhile, Douka, Brown and a handful of volunteers will continue to sift through thousands more bone fragments.
So far, they have found 1 hominin bone for about every 1,000 animal ones in this cache. At this rate, they could find as many as 400 more hominin specimens.

If you could open up any museum drawer and find one previously-unidentified hominin bone in every 1000 bone fragments, it would be a massive advance by any measure. If you could identify such bone fragments at every archaeological site, the resulting sample would provide an unparalleled record of hominin populations in the past–not to mention, we’d find a few ghosts in the process.

Most fossil settings are dominated by fragments, and most bone fragments within mixed assemblages are not identifiable to species. An advance like ZooMS should remind everyone of just how much useful biological information has been lost from sites excavated in historic times when archaeologists simply did not collect unidentifiable bone fragments. The backdirt of old archaeological sites is full of bone fragments and stone artifacts that were “not good enough” to bother cataloging and collecting. In a few cases, recent archaeologists have returned to those backfill deposits, finding bone fragments–even refitting them to broken specimens that made it into museums. Without such extraordinary luck, those massive backdirt piles remain contextless, drifting flotsam of bad archaeology. ZooMS can’t fix that problem now; the context is already gone.

Digging sites responsibly means recording and preserving context for the future. Archaeology is inevitably an act of destruction and it is not possible to retain every microscopic detail or chemical trace, especially since what makes those traces meaningful is their position and situation within a site. Recording every site at a microscopic level is not possible with today’s approaches.

Tomorrow’s approaches will be better. Testing every bone fragment has just come into the realm of possibility, but remains incredibly time and resource-intensive. It can yield huge dividends at a site like Denisova where the information can catalyze ancient DNA recovery. This kind of large-scale chemical testing may not presently justify the cost for most archaeological sites, but it will be cheaper in the future–or may help to justify a reduced intensity of digging and a higher intensity of sampling at some sites.

Recognizing how technology brings the potential for better information recovery, archaeologists must sample sites deliberately, with an eye toward what is possible today with time-intensive methods, and what must remain for the science of future generations.

The ZooMS method, as exciting as it is, relies upon collagen preserved in bone fragments, and so archaeologists can apply it only to sites where collagen is preserved, which are mostly within the past 100,000 years or so. Will we ever have a method that will allow paleontologists to make use of the fragments of bone within older sedimentary contexts? I think we will.

Related:

“A visit to La Grotte de Cotencher”

“Identifying the species used to make bone arrowheads”

Link: Identifying the species used to make bone arrowheads

The Conversation is running a neat story by Justin Bradfield that details the use of the ZooMS protein-barcoding technique on bone arrowheads from Late Stone Age archaeological sites in South Africa: “New technology tells us which animal bones were used to make ancient tools”.

The results indicate that farmers used fewer species for tool manufacture than they hunted for food. We also found that certain animal species were used for tools that didn’t appear to have been hunted for food.
We identified a narrow range of antelope from the bone tools from nine archaeological sites from Gauteng and Limpopo. Of particular interest is the presence of sable, roan, zebra and rhino. Until now, we didn’t know that these species’ bones were used to make tools in southern Africa.

The story is a popular rendering of results from a research paper out last week in Archaeological and Anthropological Sciences: “Identifying the animal species used to manufacture bone arrowheads in South Africa”.

Although this particular research doesn’t strike into the deeper-time use of bone as a raw material, such as by Neanderthals, it does show the potential of the ZooMS bone-identification method to address some of the (in my opinion fallacious) arguments about bone tools. I’ll look forward to seeing more ancient work on the species that earlier hominins used for toolmaking.

BRICS leaders meet Homo naledi

Last week, the leaders of the BRICS nations (Brazil, Russia, India, China, and South Africa) met in a joint summit in Johannesburg, South Africa, along with other leaders and government representatives. One of the unique events during the summit was a “virtual” visit to the Maropeng Visitor Centre of the Cradle of Humankind World Heritage Site.

The SA News agency wrote up a story about the visit: “BRICS leaders get a taste of Cradle of Humankind”.

The Cradle WHS is home to many famous hominin fossil sites, including Sterkfontein, Swartkrans, Cooper’s Cave, Malapa, and Rising Star. For the last year, Maropeng has been the host to an extraordinary public exhibition of the Rising Star fossil material, including the new fossils from the Lesedi Chamber. For last week’s BRICS meeting, these were joined at Maropeng by some other significant skeletal remains from the Cradle, including the STW 573 “Little Foot” skeleton from Sterkfontein, and the MH1 “Karabo” skeleton from Malapa.

The South African minister of Higher Education and Training, Naledi Pandor, led the virtual tour.

Pandor went on to give the BRICS leaders an exclusive view of three types of specimen hominin fossils that were on display. These were Homo naledi, “Little Foot” (Australopithecus prometheus) and “Karabo” (Australopithecus sediba).
It was the first time that “Little Foot” was on public display, after having been recovered from the rock in which it has lain buried for the past 3.67 million years at Sterkfontein.
The BRICS leaders were first taken through the origins of Homo naledi, one of the fascinating discoveries in human origins.
Consisting of more than 1 550 numbered fossil elements, the discovery is the single largest fossil hominid find yet made in Africa.

It’s really exciting that the South African government is so proud of the fossil discoveries, and that South African scientific work can shine in this way.

Heritage and science development are much more central to the conversation at meetings like BRICS, compared to the political and economic focus of the G7. I’d say that the larger economies have misplaced—or, maybe, shorter-term—priorities. Taking the long view might help us all find greater common ground.

'Museum of Man' to change name

This came across my feed this morning: “San Diego Museum of Man In Balboa Park Wants Your Help Deciding New Name”.

It’s a good idea—the name is confusing:

But one tourist from Europe said he thought the museum was literally just about males.
"When I was there I thought it’s only for men," Intan Devreies said. "In the Dutch language, "man" means man not humankind."
A spokeswoman for the Museum of Man said a new name will not be unveiled until 2020.

The thing is, in the twenty-first century, “Museum of Man” sounds like somebody’s idea of a hip, ironic name for a museum actually devoted to men.

Link: A visit to La Grotte de Cotencher

The SwissInfo news site has a nice article about a Neandertal site in Switzerland: “Meet a Neanderthal woman from one of Europe’s oldest cave sites”.

Now you can see the exact spot where the woman was discovered. Since early June, this cave, “La Grotte de Cotencher” – just a short drive and walk from the town of Neuchâtel – has been open to the public for guided tours. The cave is the oldest archeological site in this part of Switzerland showing human habitation. The woman’s jaw was found on a little shelf of earth the size of a dinner plate.
“We call her ‘La Dame de Cotencher”, says archeologist François-Xavier Chauvière, who has been in charge of excavations at the cave since 2016.

It’s always neat for me to see human evolution heritage tourism and public communication expanding into countries where they have not been as prominent historically. Switzerland has a history of great research in human origins, and it’s great to see expansion of Paleolithic archaeology in the country itself.

Still, I always hate to hear about the sheer amount of material removed in early twentieth-century excavations:

Those explorers had to crawl in on their bellies, bumping their heads on the low ceiling. Between 1916 and 1918, they removed some 300 cubic meters of soil and rock (and animal teeth and bones).
But now you can stand up and easily move around the 1375-cubic meter cavern. Yet, this space is still smaller than what the nomad cave clans found more than 72,000 years ago. In the Pleistocene Epoch when hunter-gatherer Neanderthals sheltered here, this cave above a stream, was considerably larger than what we see today, because, since then, millennia of earth, rock, leaf litter and the sands of time have accumulated.

Modern excavations remove very little material, and leave as much of the original profile as possible.

Three hundred cubic meters is a lane of an Olympic swimming pool. Archaeologists today have to work around the destruction of past generations, and must do their best to avoid destroying evidence that future generations might recover with new technologies.

DNA genealogy and forensic cold cases

This year there have been some amazing new leads in “cold cases” by using a new kind of DNA approach, using public genealogy websites to look for people who are similar to samples from crime scenes and thereby identifying suspects by finding their genetic relatives.

Today NBC News is running an article that reports on a new case solved with genealogy, and gives some broader perspective: “‘This is just the beginning’: Using DNA and genealogy to crack years-old cold cases”.

Then, this spring, that company, Parabon NanoLabs, called back, offering to perform a new type of DNA testing that went far beyond the traditional biometric match police labs use. Fort Wayne agreed, and six weeks later the company’s lead researcher reported that she’d narrowed the list of potential suspects to two brothers. On Sunday, detectives arrested one of the brothers, who confessed.
This seemingly rapid resolution to a long-stalled murder case is becoming something of a trend: It is the fifth cold case solved by Parabon and their researcher, CeCe Moore, since early May, meshing high-tech DNA analysis, traditional genealogical work and the soaring popularity of online ancestry databases. A sixth, involving an accused serial killer in California, was solved in a similar manner.

Some people think this is the next big step in restoring justice to victims, others think is it a major potential invasion of genetic privacy.

I haven’t written about these cases yet, but I have to say this forensic approach may be the most significant story in human genetics this year.

The dawn of bread

Archaeologists working at Shubayqa 1, a site in northeastern Jordan, found tiny fragments of an ancient unleavened bread as they were excavating a hearth. The site was made by people of the Natufian culture, 14,400 years ago. The paper describing the discovery, by Amaia Arranz-Otaegui and coworkers, documents the use of a mixed unleavened dough to make bread more than 4000 years before the introduction of agriculture in this region of the world.

The paper includes a photo of the fireplace and structure where the team found the oldest of the charred bread remains. It is one of the most beautiful site photos I’ve ever seen in an archaeological paper:

Image of the fireplace from Shubayqa 1 from Arranz-Otaegui and coworkers
Figure 2 from Arranz-Otaegui et al. 2018. Original caption: "The site of Shubayqa 1 showing Structure 1 and one of the fireplaces (the oldest one) where the bread-like remains were discovered."

Many of the bread fragments showed evidence of grain from various species. But five of them were a mixture that included tubers from a plant known as the club rush.

Ethnobotanical and experimental evidence indicates club-rush tubers are best consumed as gruel or flour to make bread, instead of boiling or steaming (18, 19). Pure club-rush tuber bread is brittle, crumbly, and flaky, but the addition of bread wheat (Triticum aestivum) flour (i.e., gluten) allows for the production of elastic dough that can be pressed onto the walls of a tandir-type oven structure and be baked (18). Evidence for cereal and club-rush tuber preparations have been identified at late Neolithic sites in Turkey (2) and The Netherlands (20). The finds from Shubayqa 1 suggest a considerably earlier date for their dietary use.

It’s a fascinating discovery that adds perspective to the systematic use of various wild plants and food preparation in these semi-nomadic people.

Link: New stratigraphy chart

The International Commission on Stratigraphy has released the 2018 version of Earth’s stratigraphic intervals, illustrated with a very helpful chart:

2018 stratigraphic chart from the International Commission on Stratigraphy

The original, in PDF format, is easily blown up to look at the dates for each interval.

Link: DNA conspiracy theories

In a post this week on the Anthropology News site of the American Anthropological Association, the sociologist Joan Donovan describes her work on DNA identity and self-described white nationalists: “Written in Blood”.

As social scientists, we wanted to know more about how white people, particularly white nationalists, interpret DNA ancestry tests to justify racial purity. It was an important question for us because we were also witnessing the early growth of a white nationalist movement, rebranded as “the Alt-Right” in 2015. Fast forward to December 2017 and the satirical website Cracked.com reported that an anonymous employee from a DNA ancestry company said that they were purposefully messing with some customers’ data in order to anger racists. How and why does a conspiracy theory like this emerge and spread?

This piece is worth reading as a contribution to the conversation on DNA and race.

I have a slightly different perspective than Donovan on this issue.

Cracked.com is in fact a satire site, and many “conspiracies” today get started as satire. But I don’t think there’s anything ridiculous about the idea of DNA genealogy companies “tipping the scales” on ancestry results. For one thing, during just the last few months, we’ve seen a number of stories in which DNA genealogy testing companies gave “Native American” ancestry to samples that (without the companies’ knowledge) had been taken from dogs.

Here’s a story describing one of these cases: “Another DNA Testing Company Reportedly Gets Fooled by Dog DNA”.

Such cases point to the real problem that some companies doing business in this area are not maintaining best practices, to say the least. Without commenting on these particular cases, consumers should make themselves aware that some DNA ancestry tests may be unscrupulous or fraudulent. Indeed, even companies recognized as legitimate businesses may have been reporting results to customers that diverge substantially from the best scientific knowledge about human genetics.

And it is well-known that even the most responsible companies base their reports of “geographic ancestry” upon samples that are very large in Europe but tiny in Africa and the Americas.

All this makes it hard even for experts to tell genuine from fraudulent results in this area, without having access to the algorithms and DNA results. For the public, such “ancestry” tests are simply a black box.

With this “Wild West” atmosphere, it is hardly a stretch to think that a company might report DNA results more skewed to political or commercial interests than to reality.

Link: A new field season of the Deep Roots project at Victoria Falls

Larry Barham of the University of Liverpool and international collaborators have a field project in Zambia examining the “Deep Roots of Human Behavior”, investigating the beginning of compound tools and the transition to the Middle Stone Age. Last year the project disseminated its fieldwork by a very successful blog.

Earlier this month, the first post of the new field season details some of their research aims as they try to understand the MSA of the Victoria Falls area.

Much of the 2017 season was spent looking for sites recorded by Desmond Clark in the 1940s and earlier. We have his maps but those were the days before GPS and there just wasn’t enough detail to re-locate most of the key sites. By way of a recap, we’re looking for sites that preserve stone artefacts from a time period roughly 600,000 to 200,000 years ago. Over this period our species, Homo sapiens, evolved, but there were at least two other human ancestors in the region that we know of, Homo naledi and Homo heidelbergensis. So we can’t be sure who made the tools we’re finding and it’s the tools we’re interested in, because they document a basic change in the way humans thought about technology.

I think it’s great that they are explicitly including multiple species as possible makers of MSA artifacts. If there were biogeographic boundaries among hominin species in Africa during the last half million years, the Zambezi basin is a key area to understand.

Ejecta rays point to the problem with 'ideal' models

The PNAS Journal Club points to an interesting research study on craters: “Journal Club: Researchers may’ve finally solved mystery of crater ray formation”.

The problem is that craters on celestial objects like the Moon are surrounded by distinct rays of ejecta, but those didn’t form in experiments at high velocity.

Full moon showing ejecta rays around craters
Photo: Renden Yoder

Why did the model fail to generate the real-world phenomenon of ejecta rays? Because the model conditions were too ideal:

The team tried to vary every parameter they could imagine—changing the grains’ diameters, mixing grains of different sizes, increasing the speed of the balls—but the eventual solution came about by accident. One day, Chakraborty’s fatigued postdoc, Tapan Sabuwala, failed to follow normal protocols and smooth down the surface of their sandbox before dropping in their impactor. After the drop, voilà—a beautiful crater and its rays appeared.
The jagged landscape, which schoolroom students naturally produced when they haphazardly dumped out their bags of flour, seemed to be the key to creating crater rays. The team followed-up with 135 more experiments in which they pressed a repeating hexagonal honeycomb pattern into their granular surface and found that they could consistently make rays. Moreover, the number of crater rays depended on only two factors—the size of the impactor and the spacing of the hexagonal bumps.

There is a strong rationale to use simple models in physics. You want the conditions to be easily described with mathematics, and easily replicable by other scientists, so you specify exactly the ideal conditions for the model.

But the kids were using an even simpler model, in the sense that anybody can make a pile of flour and throw stuff at it. What is ideal is not necessarily simple. In this case, the real-world physics of planets and asteroids is more similar to the real-world physics of particles than the ideal physics of surfaces and ballistics.

As I read this story, I thought about genetics. We use a lot of “simple” ideal models in human genetics. The hypothetical reconstructions of populations like the “Basal Eurasians” are based upon ideal panmictic populations with mathematically ideal genetic exchanges. The quantification of Neanderthal genetic contributions to humans has likewise been based upon ideal population models and discrete mixture events.

These ideal populations may be easy to model with math, but they bear little resemblance to the spatial heterogeneity of living human populations or the irregular temporal distribution of mixture and contact.

What would a more realistic model look like? For human populations, it would have heterogeneity—not populations as single points, but populations with a spatial extent, varying degrees of mixture as they came into contact, and biased growth.

Would the outputs of such a model look more like the real world? It’s not easy to say. Possibly there is no real difference, and the more complex models come with a greater danger of overfitting because they add so many parameters.

But not all parameters are created equal. My biggest concern about simplistic population models is that they fit data better when new point populations and sources of mixture are added. What if some of those “ghost populations” are really not necessary, if we examine a more complex, more realistic model?

Today’s most surprising findings about human prehistory are pretty strongly model-dependent, and few population geneticists are examining the effect of model selection on these conclusions.

Reinforcing the antiquity of hominins in China

In Nature yesterday, Zhaoyu Zhu and collaborators published a paper describing the paleomag chronology of Shangchen, a site in Lantian county, China. The oldest layers bearing stone artifacts at this site appear to be approximately 2.1 million years old, making these stone tools the oldest yet documented within China.

I was really interested in seeing this new archaeological study published. China is taking on a much more important role in human evolution research. The science of human evolution has advanced markedly within China during the last 20 years, just as it has in many other parts of the world. I had the great privilege of visiting the Institute for Vertebrate Paleontology and Paleoanthropology in Beijing earlier this year, and I’ll be sharing more from that trip soon.

The Shangchen site shows two things clearly.

First, it confirms that there were hominins making stone tools in this part of China by 2.1 million years ago. That’s not the earliest date ever found in China — another cave site called Longgupo has stone tools that archaeologists think are 2.2 million years old or older. But other archaeologists have questioned the very early dates from Longgupo, so this new Shangchen chronology helps to put the early evidence on a more secure footing.

Second, the Shangchen site is not merely one ancient discovery but a long series of archaeological layers. With seventeen archaeological layers across the period from roughly 1.4 million to 2.1 million years ago, Shangchen presents a more impressive record of habitation of the Chinese Loess Plateau than any other part of Eurasia.

Loess stratigraphy showing position of artifacts from Zhu et al. 2018
Figure 3 from Zhu et al. (2018), showing the loess and paleosol stratigraphy at Shangchen. The position of artifact-bearing layers in the deposit is shown at left, while the global paleomag chronology is at far right. There is an impressive correlation between the paleomag signatures at the site and the global paleomag chronology.

Still, seventeen artifact-bearing layers in 700,000 years leaves a lot of room for significant changes and hiatuses. At some times, the climate in this region was very arid, the deserts of western and northern China became larger, and huge amounts of dust blew from those deserts and dropped onto this central part of China. At those times, there are some archaeological layers but not too many. Other times, the climate was moist, less dust blew from the deserts, and stable layers of soils formed on the surface at Shangchen. Those ancient paleosols are richer and denser in stone tool assemblages.

So this site seems to show evidence of a long habitation of China by human relatives, but whether it was the same hominin species or population across all that time is not clear. Whoever was living there, they were responding to the local climate in the way they behaved in this region.

Large areas of central and western China are covered in loess from the early Miocene period—as early as 22 million years ago—on up to recent times. During relatively arid periods, desert expanded in western and northern China and Mongolia, generating large amounts of windblown dust. Some of this dust settled in western and central China, creating layers of loess. Today, a thick succession of loess deposits occur in the Chinese Loess Plateau. The sediment is composed of fine particles that were carried by the wind. During wetter periods, the loess deposition greatly slowed, and stable soils formed on the ground surface, so today’s stratigraphy is an alternating series of loess layers and paleosols.

Water easily erodes these layers, so gullies and streams create deep cuts across the stratigraphy. Of course, hominins didn’t enter China as early as the Miocene, as far as we know. Archaeologists have focused on the Pleistocene stratigraphy of the Loess Plateau, surveying these layers where stone tools contrast markedly with the fine-grained loess. A huge region of China is covered by these ancient windblown sediments, and there have been many, many important archaeological discoveries, from Upper Paleolithic all the way back to the dawn of hominin occupation of China.

The paleomagnetic chronology presented in this paper is only one aspect of a much larger program of dating loess events across the Pleistocene. The systematic approach to identifying these dry time periods with large loess deposits is really important, because it is allowing scientists to tie together ancient landscapes and evaluate tools and fossils from many different sites.

For example, the same approach gave rise to the redating of the Gongwangling fossil material by the same research group in 2015. (They argued that the fossil is around 1.65 million years old, far more ancient than thought previously.) This program of chronology across sites has been underway for several years, and I think it is going to lead to many more important discoveries.

I’ll be writing a bit more in the next few days about what scientists know about the earliest movements of hominins out of Africa. All the headlines I’ve seen in the last day are wrong.

Every story I’ve seen has accentuated that Shangchen is 300,000 years older than Dmanisi, which the stories claim was previously the oldest evidence of human habitation of Eurasia. This is wrong.

Now, Dmanisi is very important, but it’s simply not accurate that it’s the oldest evidence outside Africa. There are older sites. Even within China, Longgupo has an earlier published chronology, and Longgudong is estimated to be as old as the oldest Shangchen layer. In India, there are sites with earlier published evidence, one as old as 2.6 million years.

That doesn’t mean scientists should blindly accept every “earliest” date for every archaeological occurrence. Any find that demands that we revise our models for human evolution should be supported by multiple lines of evidence. So when only one or two methods point to the geological age, I want to see more. Early sites often have only a few observations suggesting a minimum age, and history shows that those “earliest” dates are often revised. Even for the new Shangchen chronology, where the paleomagnetic chronology is impressive, we should seek more cross-validation.

Still, even with my mistrust of geological age estimates, I have to say that the evidence points against the old idea that the first out-of-Africa dispersal was by stone tool-making Homo erectus within the last 2 million years.

We now have five or six sites earlier than Dmanisi, and Dmanisi itself is the first occurrence of “H. erectus” anywhere in the world. With the Gongwangling cranium and the earliest Sangiran material older than 1.5 million years, H. erectus has a better record and greater diversity in Eurasia than in Africa in the same time period.

At least, what we’ve been calling H. erectus. If there was a single, early colonization of Eurasia by hominins, it must have been much earlier than the first occurrence of H. erectus. I would suggest instead that there were many movements and dispersals from Africa and back into Africa, starting much earlier than 2 million years ago and extending up to the most recent. We already know this is true of the Middle and Late Pleistocene—it is not a single dispersal and stasis, there were many partial replacements with interaction of earlier people and new migrants.

The old H. erectus single migration model just can’t account for the data of early sites in Eurasia, it doesn’t deal well with the morphology of the Dmanisi and early African H. erectus fossil material, and it doesn’t add any explanatory power.

There’s a big story brewing here.

References

Zhu Z, Dennell R, Huang W, Wu Y, Qiu S, Yang S, Rao Z, Hou Y, Xie J, Han J, Ouyang T. 2018. Hominin occupation of the Chinese Loess Plateau since about 2.1 million years ago. Nature (online). doi:10.1038/s41586-018-0299-4

Zhu, Z. Y., Dennell, R., Huang, W. W., Wu, Y., Rao, Z. G., Qiu, S. F., ... & Zhou, H. Y. (2015). New dating of the Homo erectus cranium from Lantian (Gongwangling), China. Journal of Human Evolution, 78, 144-157. doi:10.1016/j.jhevol.2014.10.001

A pre-Clovis tradition from the Gault site, Texas

The Gault site, on Buttermilk Creek near Austin, Texas, is one of the most significant early American archaeological sites. The whole site covers an enormous area, with excavations that have been carried out formally and informally for more than a hundred years. Scientific investigation of the site in recent decades has focused upon a number of distinct excavation areas.

This week, Science Advances published a new paper by Thomas Williams and coworkers describing their work in Area 15 of the Gault site. Their paper documents a rich, previously unknown culture that existed more than 16,000 years ago.

They call this early tradition the “Gault Assemblage”.

Gault assemblage artifacts from Williams et al. (2018)
Gault Assemblage artifacts from Williams et al. (2018). Original caption: "Gault Assemblage artifacts (A to D, F, and L) Bifaces. (E) Blade core. (G) Quartz projectile point. (H and I) Projectile points. (K) Projectile point tip. (M, V, and W) Blade. (N) Unifacial tool. (O and T) Gravers. (P) Discoidal biface. (Q) End scraper. (R to U) Modified flake tools. (X and Y) Lanceolate projectile points. Descriptions are given in the Supplementary Materials."

A number of sites in North America preserve artifacts proposed to be earlier than the spread of the Clovis tradition, around 13,500 to 11,500 years ago. The Gault site is very interesting because it presents a pre-Clovis archaeological tradition in stratified context beneath Clovis archaeological material. The new paper provides an optically-stimulated luminescence (OSL) chronology for the entire archaeological sequence at the site. The team obtained age estimates for four samples from the Gault Assemblage layers, which all lie between 16.7 and 21.7 thousand years ago. They also dated four samples from the overlying Clovis layers, all between 11.9 and 13.2 thousand years ago.

Stratigraphy and OSL chronology of the Gault area 15 site, from Williams et al. (2018).
Figure S4 from Williams et al. (2018). Original caption: "Relationship between the stratigraphy and cultural components in Area 15. Stratigraphic unit numbers are shown in the stratigraphic interpretation and the cultural horizons are highlighted in gray."

There is not a sterile layer between Clovis and Gault Assemblage, but the flake count in that interval is quite low, and the Clovis itself is low-representation compared to the much earlier Gault Assemblage layers. It would seem hard to explain away this assemblage as a product of artifact migration downward from Clovis or later layers.

That is relevant because several years ago, a team of scientists criticized the interpretation of another pre-Clovis assemblage stratified beneath Clovis material. This site, also on Buttermilk Creek, is called the the Debra L. Friedkin site, with the pre-Clovis material first published by Michael Waters and colleagues in 2011 in Science. In Waters’ and colleagues’ (2011) description, a pre-Clovis artifact assemblage between 15.5 and 13.2 thousand years ago is stratigraphically below Clovis at the site, and differs from the Clovis assemblage in many ways. Waters and coworkers called this the “Buttermilk Creek Complex”. They suggested that this was evidence for a tradition earlier and different from Clovis.

Juliet Morrow and colleagues (2012) objected to this interpretation. They offered the alternative interpretation that (a) the apparently early age of this assemblage might be the result of downward migration of isolated artifacts from higher, Clovis layers, and (b) even if the site itself is chronologically early, it may simply be an early variant of the Clovis tradition.

Jennings and Waters (2014) responded with a statistical comparison of Buttermilk Creek Complex with Clovis, concluding that they are different and distinguishable on technical grounds, although the Buttermilk Creek might have been antecedent to the Clovis. And Driese et al. (2013) undertook a close analysis of the sediments, concluding that layers were not mixed, and downward vertical displacement of material could not have been substantial.

I review this mainly to show that a number of archaeologists found the earlier claim of a stratified pre-Clovis-to-Clovis context to be controversial, and it gave rise to both a published critique and subsequent research. I imagine that similar criticism may emerge of this current research study.

In the new paper on the Gault site, Williams and colleagues do not provide a comparison between the Gault Assemblage and the Buttermilk Creek Complex. Considering that the Gault Assemblage may be 2000 years or more earlier than the pre-Clovis material from the Debra L. Friedkin site, they may not be comparable. But this seems like an obvious comparison that I’d like to see.

As an aside, for those who want to know more about work at the Gault site, earlier this year, SAPIENS ran a book excerpt by Craig Childs about the site. This gives some nice context for the excavations: “In the Land of the Mammoth Eaters”.

References

Williams TJ, Collins MB, Rodrigues K, Rink WJ, Velchoff N, Keen-Zebert A, Gilmer A, Frederick CD, Ayala SJ, Prewitt ER. 2018. Evidence of an early projectile point technology in North America at the Gault Site, Texas, USA. Science Advances 4: eaar5954. doi:10.1126/sciadv.aar5954

Waters MR, Forman SL, Jennings TA, Nordt LC, Driese SG, Feinberg JM, Keene JL, Halligan J, Lindquist A, Pierson J, Hallmark CT, Collins MB, Wiederhold JE. 2011. The Buttermilk Creek Complex and the Origins of Clovis at the Debra L. Friedkin Site, Texas. Science 331: 1599-1603. doi:10.1126/science.1201855

Morrow JE, Fiedel SJ, Johnson DL, Kornfeld M, Rutledge M, Wood WR. 2012. Pre-Clovis in Texas? A critical assessment of the “Buttermilk Creek Complex”. Journal of Archaeological Science. 39:3677-3682. doi:10.1016/j.jas.2012.05.018

Jennings TA, Waters MR. 2014. Pre-Clovis lithic technology at the Debra L. Friedkin site, Texas: Comparisons to Clovis through site-level behavior, technological trait-list, and cladistic analyses. American Antiquity. 79(1):25-44. doi:10.7183/0002-7316.79.1.25

Driese SG, Nordt LC, Waters MR, Keene JL. 2013. Analysis of site formation history and potential disturbance of stratigraphic context in vertisols at the Debra L. Friedkin archaeological site in central Texas, USA. Geoarchaeology. 28:221-248. doi:10.1002/gea.21441

Looking at Luzon hominins, from the perspective of 1985

In light of this week’s paper by Ingicco and colleagues showing evidence of 700,000-year-old human activity from Kalinga, on Luzon, I’ve been doing a little reading.

I found an interesting article by Lawrence Heaney, published in the 1985 volume of Modern Quaternary Research in Southeast Asia. The title is: “Zoogeographic evidence for Middle and Late Pleistocene landbridges to the Philippine Islands”. In case you wonder about the title, the article shows that there were no land bridges to the Philippines, although there were several ancient land bridges connecting various islands within the Philippines.

The part worth quoting at length has to do with speculations that Homo erectus may have reached the Philippines.

Comments on Homo erectus and land bridges
Given the strong evidence against land bridges from Asia to the Philippines, what does this tell us about the probability of finding Homo erectus in the Philippines?
First, it must be recognized that this analysis has been general; it has not dealt with any specific species, and does not prove that a single species cannot behave in a different fashion from most or all others. The fact that a single species of monkey, Macaca fascicularis, is now recognized to occur in much of Southeast Asia including nearly all of the Philippines, could be taken as evidence that it is possible, however unlikely, that Homo erectus had a similar distribution.
However, it must also be recognized that if Homo erectus did occur on Luzon, for example, they arrived there by crossing over several sea channels that were over 10 km wide, and could have been over 25 km wide. It is possible to imagine a small population of monkeys floating accidentally out to sea on a mass of trees and branches and being rafted to an island 25 km away; it is far, far more difficult to imagine a similar thing happening to a group of proto-humans. Thus, I suggest that if Homo erectus did occur on Luzon, they arrived by deliberate construction of rafts and dispersal across sea channels.

The chapter goes on to consider whether any evidence about Homo erectus on Java suggested that they might have crossed water to islands. This discussion is a bit outmoded from today’s perspective: Although it has long been known that Java was connected to the Asian mainland during the Late Pleistocene, it was not always so evident that all of Java had such connections during the Early Pleistocene, since the island has coalesced as a result of Pliocene and Early Pleistocene uplift and volcanism. So some authors had suggested that the earliest evidence of Homo erectus on Java might have occurred before Trinil was part of the Asian landmass, for example.

More relevant today is that we now know that hominins occupied Flores, Sulawesi, and now Luzon, all prior to 100,000 years ago. Flores and Luzon were peopled during the early Middle Pleistocene.

What’s more, the Flores hominins may represent a hominin group that diverged earlier than the last common ancestor of Homo erectus and archaic and modern humans. This is not a question of Homo erectus dispersing to islands, it may be a question of a branch of hominins that–except for H. floresiensis–is presently unknown.

Link: Are physicists barking up the wrong tree?

Sabine Hossenfelder has a book coming out next month, Lost in Math: How Beauty Leads Physics Astray. She pursues the question of why physicists today follow research paths toward “beautiful” or “natural” theories, and critically examines past theories, noting that successful ones were rarely viewed as “beautiful” at the time they were proposed.

The implication is that today’s efforts to develop new theories may be barking up the wrong tree.

She has done an interview with Edge.org on her work: “Looking in the Wrong Places”, which is both thoughtful and provocative:

The problems that I see in my own community worry me a lot. Not so much because I’m so terribly worried about quantum gravity. On a certain level, even though it’s my personal interest, I realize that for most of the people on the planet making progress in quantum gravity is not that terribly important. It worries me because I have to question how well science itself is working.
The problems that I was speaking about in my own community—that people work on certain topics just because the money is there, because it’s something that is popular and that their colleagues appreciate—are problems that almost certainly exist in most scientific communities. My extrapolation from my own field would tell me that I should be very skeptical about whatever comes out of the scientific community. And that’s not good. Clearly that’s not good.

I’m looking forward to this book.