Philippa Kaur

Cast of the Sahelanthropus tchadensis skullDidier Descouens CC BY-SA 4.0
This is an extract from Our Human Story, our newsletter about the revolution in archaeology. Sign up to receive it in your inbox for free every month.
The period between 7 million and 4 million years ago is a bit of a nebulous phase in the story of human evolution. There are basically four data points: Sahelanthropus tchadensis from 7 million years ago, Orrorin tugenensis from 6 million years ago and the two species of Ardipithecus from 5.6 million and 4.4 million years ago. Each is known from a handful of incomplete fossils. For a period of 3 million years, that’s not much. For comparison, there are dozens of Neanderthal sites from the past 500,000 years.
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This means that the few fossils we have from the nebulous phase of hominin evolution have taken on an outsized importance. Every detail of their interpretation is scrutinised and discussed endlessly.
Despite being the oldest known hominin, Sahelanthropus is a relatively recent discovery, first described in 2002 by a group of researchers largely based at the University of Poitiers in France. The remains were found in the deserts of Chad, which is in north-central Africa, a long way from eastern countries of the continent like Ethiopia and Tanzania that had yielded many famous fossils.
The main find was a skull, which was named Toumaï. In New Scientist’s report at the time, writer Jeff Hecht said it didn’t resemble any modern great ape: “Although its body and brain were the size of a modern chimp’s, its face was quite different, with large brow ridges and much smaller canine teeth.” The researchers also found some teeth and bits of jawbone.
What they didn’t find were leg bones. This was unfortunate, because leg bones ought to tell us about how Sahelanthropus walked: did it walk on two legs like us and many later hominins, did it knuckle-walk like a chimpanzee or did it do something else entirely?
The French researchers who described Sahelanthropus argued it was bipedal. This was based mainly on the base of the skull and how it apparently fitted onto the spine: it looked like the skull sat directly atop the spinal column, as opposed to being at an angle like in an ape skeleton. It was an intriguing argument – but far from conclusive.
For the better part of two decades, this was largely how things rested. Which was weird, because, in fact, limb bones had been found: the original team had found a femur (thigh bone) and two ulnas (forearm bones). A student at the University of Poitiers, Aude Bergeret-Medina, identified the femur as belonging to Sahelanthropus in 2004. Her tutor, Roberto Macchiarelli, supported her. However, they were denied further access to the bone.
In 2018, the pair tried to present their own analyses of the femur at a conference at the University of Poitiers, but they were blocked by the organisers. Other palaeoanthropologists criticised this decision. John Hawks at the University of Wisconsin-Madison wrote a blog post that, while couched in polite academic language, was basically furious. “All of the critics could be silenced within hours by data and evidence,” Hawks wrote. “Instead, silence about these key fossils has reigned for fifteen years.”
3D models of the femur (left) and ulnae (centre and right) of Sahelanthropus tchadensisFranck Guy/PALEVOPRIM/CNRS – University of Poitiers
The following year, Macchiarelli and Bergeret-Medina submitted a paper about the femur to the Journal of Human Evolution, which was finally published in November 2020. The key point was that the Sahelanthropus femur was curved. This is typical of a great ape like a chimpanzee, and not what you’d expect of an upright-walking hominin. Our leg bones are straight because they need to act like pillars supporting the entire weight of our bodies. I consulted two independent palaeoanthropologists, including the discoverer of Orrorin, and they both agreed: Sahelanthropus didn’t look like a biped.
However, the original Poitiers research team, after years of silence, decided to start talking. In September 2020, two months before the publication of Macchiarelli and Bergeret-Medina’s new paper, researchers led by Franck Guy (a co-author of the original Sahelanthropus paper from 2002) and Guillaume Daver at the University of Poitiers released a preprint, which was eventually published in Nature in 2022.
Guy and his colleagues highlighted a number of features of the femur that they say indicate bipedality. For instance, thicker regions along the shaft of the bone correspond to those seen in modern humans and are different from those in great apes. There was also “a rough surface at the top of the femur where the buttock muscles attach”.
So, case closed? Not quite.
No to bipedalism
In June, a team that included Macchiarelli and Bergeret-Medina published a response in the Journal of Human Evolution. The paper is a point-by-point rebuttal of Guy and Daver’s paper.
“Most of the analysis they published in this paper [does] not show any signal of bipedalism, in our opinion,” says Clément Zanolli at the University of Bordeaux in France, one of the authors of the new study. Features that Daver and Guy claimed were solely found in later bipedal hominins can actually be found in some older ape species, which weren’t bipedal.
For example, the top end of a femur has a ball-shaped bit sticking out, which fits into the pelvis. This ball is missing from the Sahelanthropus femur, but we do have the section immediately below. This includes a thickened section called the calcar femorale, which helps support the weight of the body.
“It was supposed to be a hallmark of bipedalism,” says Zanolli. Daver and Guy interpreted the presence and shape of the calcar femorale as evidence that Sahelanthropus habitually walked on two legs. However, “this feature is actually found also in African apes and in many primates,” says Zanolli. So, he argues, it isn’t useful for deciding whether a species was bipedal.
Zanolli’s team also reanalysed the two arm bones, in order to estimate the relative lengths of Sahelanthropus’s arms and legs. Bipedal hominins have proportionally longer legs and shorter arms than knuckle-walking apes, so this is another clue to how Sahelanthropus got around. On this measure, the team found that Sahelanthropus was most similar to modern gorillas and orangutans, and nowhere near bipedal hominins like Australopithecus or Homo.

The paper has other analyses, but you have probably got the gist at this point. The overall message is that the few pieces we have of Sahelanthropus’s limbs don’t show strong evidence of habitual bipedal walking. “It’s generally indistinguishable from the African apes,” says Zanolli.
At this point, you will be wondering what the authors of the 2022 paper have to say about all this. I’m afraid you will have to keep wondering, because Guy declined to comment. He told me that he and his colleagues are writing a reply, which will be published in the same journal, and which they expect to have finished “before August”. He didn’t want to discuss the results until that was done.
Meanwhile, some of Zanolli’s colleagues are pressing ahead with analyses of computer tomography (CT) scans of the bones. Not all of them, though, because some members, including Zanolli, were denied access by the government of Chad. Zanolli says this is highly unusual: “In most countries I’ve been, it’s quite easy, or at least it’s possible, to access fossil material.” He says this is the only time he has been denied access.
Other parts of the skeleton could also shed more light. “I think the teeth should be investigated further,” says Zanolli. “There is not really a paper published on the teeth.”
The future of the past
Finally, let’s step back from the details of the Sahelanthropus fossils and put them into their full context.
As a first step, suppose Zanolli and his colleagues are right. That means Sahelanthropus isn’t bipedal and possibly isn’t even a hominin. That doesn’t mean it’s suddenly a boring fossil. If anything, it becomes even more important.
That’s because Sahelanthropus would become a key fossil for the evolution of African great apes. That’s something we know almost nothing about. “If it’s an ancestor of gorillas, for example, it would be also fantastic, because we have not a single fossil for the ancestors of gorillas,” says Zanolli.
More broadly, it would help to find more hominin and ape fossils from that nebulous time between 7 million and 4 million years ago. Zanolli says part of the problem is that much of central Africa was tropical forest at the time, and some of it still is: fossils tend not to be preserved in such places. Still, there are places like Chad that are promising but under-investigated.
At the moment, this gap in the fossil record is a target for fascinating but unproven speculations. When and where did bipedality evolve? Did it evolve only once in one lineage of apes, or multiple times independently? What evolutionary pressures led to the emergence of bipedal hominins?
For now, we can’t even be sure that bipedality evolved in Africa. It’s tempting to think so, because the oldest bipedal hominins we know of are African, even if you discount Sahelanthropus. A study published in May combined the locations of known hominin and ape fossils and their suspected relationships, and concluded that the group that includes both chimpanzees and hominins probably originated in north-central Africa.
But animals do move around, especially over millions of years. While apes originated in Africa 26 million years ago, climatic shifts meant that for millions of years, they were more widespread and diverse in Eurasia, before largely moving back to Africa later on. A minority of researchers claim that European apes had signs of bipedal walking as early as 11.6 million years ago. There are also hominin-like footprints on the Greek island of Trachilos, which are 6.05 million years old – about on a par with Orrorin and a million years younger than Sahelanthropus. For added variety, a study from February claimed a key role in the story for Lufengpithecus, apes that lived in what is now China around 6 million years ago.
The evidence for bipedality evolving in Eurasia rather than Africa is strongly contested, because it’s based on incomplete and even fragmentary skeletons. But so is the idea that Sahelanthropus was a biped. Again, this is why I describe this whole period as nebulous.

As for how and why bipedalism evolved, we don’t know. Not that this has stopped people coming up with ideas. A paper from March suggested that the last common ancestor of hominins and other African apes lived in Eurasia, but that a dramatic event separated the population into two, which then evolved independently.
What dramatic event? Why, the Zanclean Megaflood of course. If you don’t know, there was a period between about 6 million and 5.3 million years ago when the Mediterranean almost entirely dried out. The Strait of Gibraltar, which connects the Mediterranean to the wider Atlantic, closed – and the sea gradually evaporated, leaving hypersaline lakes. This was the Messinian Salinity Crisis.
Then, around 5.3 million years ago, the Strait of Gibraltar reopened – and the waters of the Atlantic came rushing in. One reconstruction estimated that it took “from a few months to two years” to refill the Mediterranean basin, which, if not an apocalyptic mega-tsunami, is still pretty fast.
Supposedly, this Zanclean Megaflood cut off one population of apes/hominins on the Arabian peninsula, while others were able to reach Africa – creating an evolutionary split. In May, a separate group went further and linked the closure and reopening of the Mediterranean to changes in the behaviour of the Pacific tectonic plate. In this view, the evolution of bipedality and/or hominins was driven by geological processes on the largest scale.
You may be able to tell that I’m unconvinced by all of this. It seems to me there are far too many intermediate steps from the Pacific tectonic plate and the Zanclean Megaflood to hominins habitually walking upright, and we can’t be sure about any of them. We don’t even know the timing of the origin of bipedality. If either Sahelanthropus or Orrorin was bipedal, the behaviour evolved well before the megaflood.
So, much as I want to link the origin of hominins to the biggest flood of the past 10 million years, I think we probably ought to find some more fossils first.

Topics:human evolution More

adobe stock/Phoebe Watts
Nobody  doubts that Albert Einstein had a brilliant mind. But the Nobel prizewinner, famous for his theories of special and general relativity, wasn’t blessed with a big brain. “It was smaller than average,” says Jeremy DeSilva at Dartmouth College in New Hampshire.
This seems surprising. Big brains are a defining feature of human anatomy, and one we are proud of. Other species might be speedy or powerful, but we thrive using the ingenuity that comes with a large brain. Or so we tell ourselves. Einstein’s brain hints that the story isn’t so simple – and recent fossil discoveries confirm this. Over the past two decades, we have learned that small-brained hominin species survived on Earth long after big-brained ones appeared. Moreover, evidence is growing that they were behaviourally sophisticated. Some, for instance, made complex stone tools that could probably only have been fashioned by individuals with language.
These discoveries turn the question of human brain evolution on its head. “Why would selection favour big brains when small-brained humans can survive on the landscape?” says DeSilva. Neural tissue consumes lots of energy, so big brains must surely have brought benefits to the few species that evolved them. But what?
An answer to this puzzle is beginning to emerge. It looks like brain expansion began as an evolutionary accident and then led to changes that caused this growth to spiral. Surprisingly, the sorts of changes that drove this expansion could also explain a more recent 10 per cent reduction in human brain size. What’s more, this suggests our brains may shrink further still – and might even cause humanity’s demise.
It is undeniable that… More

A hoard of Roman gold coins found below the floor of a Roman house in Corbridge, UKWorld History Archive/Alamy
After the Romans conquered Britain in AD 43, the technologies and laws they introduced led to centuries of economic growth of a kind once thought to be limited to modern industrial societies. That is the conclusion of an analysis of thousands of archaeological finds from this time.
“Over that period of about 350 years, you’re looking at roughly a two and a half [fold] increase in productivity per capita,” says Rob Wiseman at the University of Cambridge.
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It has long been believed that economic growth in the ancient world depended on having more people and more resources, says Wiseman: to increase food production, say, required more land and more farm workers. This kind of growth is known as extensive growth.
By contrast, economic growth today is driven mainly by increased productivity, or intensive growth. Thanks to mechanisation and better breeds of plants and animals, for instance, more food can be produced from the same area of land with fewer workers.
Some recent studies have challenged the idea that intensive growth occurred only after the industrial age began, inspiring Wiseman and his colleagues to look at growth in Roman Britain from AD 43 to 400.
The team’s research was made possible by UK laws requiring archaeological investigations to be done when a site is developed, says Wiseman. “The result is there’s been tens of thousands of archaeological excavations done in this country. And, moreover, that data is publicly accessible.”
By looking at how the number of buildings changed over time, the researchers were able to get an idea of how the population of Roman Britain grew. There is a strong relation between the number of buildings and population size, says Wiseman.
To get an idea of economic growth, the team looked at three measures. One was the size of buildings, rather than the number of them. As people grow richer, they build bigger houses, says Wiseman.
Another measure was the number of lost coins found in digs. “These are things that have fallen through the floorboards, or they’ve been lost in the baths, or something like that,” he says.
The idea is that the more coins are in circulation, the more are likely to be lost. The team didn’t count hidden hoards of coins, as these reflect instability rather than growth.
The third measure was the proportion of crude pottery, such as cooking pots and storage pots, to more ornate pottery like decorated plates. Economic growth requires people to interact more and socialise more, which means “showing off” when guests are present, says Wiseman.
Based on these measures, the team found that economic growth exceeded that expected from population growth alone. They estimate that per capita growth was around 0.5 per cent between AD 150 and 250, slowing to around 0.3 per cent between AD 250 and 400.
“What we’re able to show is yes, after the Romans arrived, there was definitely intensive growth,” says Wiseman. The pace of growth rather than the kind of growth is what probably distinguishes the modern world from the ancient one, he says.

The researchers think that this growth was driven by factors such as the roads and ports built by the Romans, the laws they introduced making trading safer, and their technologies, such as more advanced grain mills and better breeds of animals for ploughing.
The higher growth between AD 150 and 250 may be a result of Britain catching up with the rest of the Roman world, says Wiseman. “You’re moving from a small tribal society where there’s not a lot of interaction going on to a world-spanning economy.”
What isn’t clear is whether this economic development made people happier or healthier. “Just because the productivity is going up doesn’t automatically mean that the welfare of Britons who were invaded and colonised was better under Rome,” says Wiseman. “That’s an open question.”
To investigate this, the researchers now plan to look at human remains to work out things such as how long people lived.
“I am convinced that they are right and that, indeed, intensive growth took place in Roman Britain,” says Alain Bresson at the University of Chicago, Illinois.
“A lot of archaeologists have noted compelling evidence for economic growth in Roman Britain, but this paper adds a welcome formal theoretical dimension to the discussion,” says Ian Morris at Stanford University, California.
However, Morris suspects that the lower average growth rate from AD 250 to 400 actually reflects high growth followed by rapid decline as the Roman empire began to break up. Further studies will resolve this, he says.

Topics:archaeology/economics More

Tonje Bøe Birkeland as Tuva Tengel on a camel in Mongolia.Tonje Bøe Birkeland
The imagined female scientists, explorers and adventurers seen in Tonje Bøe Birkeland’s photographs are echoes from a footnote in women’s history. In her ongoing series, The Characters, the photographer frames herself in the guise of Victorian and early-20th century pioneers – dressed in period costume, holding binoculars and bellows cameras – snapped in widescreen vistas of mountains, fjords and ice flows. Each picture is a performance.
Tonje Bøe Birkeland
The project began in 2008, when Birkeland was on a course about photography’s role in shaping historical truths. “It was all about did Neil Armstrong go to the moon? Did Roald Amundsen actually get to the Pole first?” she recalls. “That made me want to do something about women.” Her first character was a glaciologist.Advertisement
Tonje Bøe Birkeland
Her photographs are puzzles and her work taps into the names, appearances and biographies of real, unrecognised women, such as Louise Arner Boyd, a polar scientist who traversed the north-east coast of Greenland in the 1920s. As well as stepping into the boots of her creations, Birkeland writes their journals and creates installations of their travel cases (packed with maps and geological samples), which she both photographs and exhibits. She has immortalised her intrepid alter egos in various settings, from the snowdrifts of Svalbard to the foothills of Bhutan.
Tonje Bøe Birkeland
In the top photo, she is seen as desert traveller Tuva Tengel on a camel in Mongolia. The three other photos show her as Arctic explorer Anna Aurora Astrup in Greenland.
Birkeland’s work will be at Forum Box in Helsinki, Finland, from 22 August to 19 September.

Topics:photography/exhibition More

Tracing of the cave painting showing a pig and human-like figures from Leang Karampuang on Sulawesi, IndonesiaGriffith University
A painting of a pig with human-like figures in an Indonesian cave is at least 51,200 years old, making it the earliest known example of representational art in the world.
“We like to define ourselves as a species that tells stories, and this is the oldest evidence of that,” says Maxime Aubert at Griffith University in Gold Coast, Australia.
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The pig artwork was discovered in 2017 on the ceiling of the limestone cave of Leang Karampuang on the island of Sulawesi.
In 2019, Aubert and his colleagues dated a hunting scene from a nearby cave named Leang Bulu’ Sipong 4 to a minimum of 43,900 years old.
Now, they have used a new, more accurate technique to estimate the ages of both artworks. They found that the image at Leang Bulu’ Sipong 4 is actually more than 4000 years older than previously thought – and the Leang Karampuang art is even older.
The artworks at both locations are at least 10,000 years older than the oldest European rock art, says Aubert.
Modern humans, Homo sapiens, had reached Australia by 60,000 to 65,000 years ago, so we know they were in the region at this time, says Aubert. “We assume these paintings were made by modern humans.”
In the same caves, there are depictions of creatures with both human and animal attributes, indicating spiritual beliefs.
“This rock art is not just small symbols,” says team member Renaud Joannes-Boyau at Southern Cross University in Lismore, Australia. “They were actually painting hunting and life scenes and they were already telling stories with their art, living in a spiritual world and trying to make sense of the environment around them. That tells us a lot about the evolution of Homo sapiens.”
The previous method of dating the artworks relied on the chemical extraction of samples and a large portion of the rock had to be crushed and destroyed.
In the new technique, a 5-millimetre diameter core is extracted from the crust on the rock. From the surface of this core, material that is less than half the thickness of a human hair is removed by a laser and tested to measure the decay of isotopes in the mineral. Once this is done, the core can be plugged back into the rock art, resulting in far less destruction compared with the previous method.
Karampuang Hill, location of Leang Karampuang caveGoogle Arts & Culture
Joannes-Boyau says the new technique is likely to lead to major revisions of rock art history around the world.
Kira Westaway at Macquarie University in Sydney, Australia, says the refined dating technique has provided a more accurate assessment of when the Sulawesi art was actually painted.
“This is hugely significant, when the original age was already considered groundbreaking,” she says. “This has massive implications for our understanding of the capabilities of the early artists moving through Indonesia and the type of skills and tool kit they already possessed when entering Australia.”
Homo sapiens probably wasn’t the only species with the capacity for complex symbolic practices, says Martin Porr at the University of Western Australia. “It is very likely that other hominins at least had some capabilities in this respect as can be inferred from the highly sophisticated material culture of Neanderthals.”
“It will be important to do more work in the future on the archaeological evidence in the region to understand and confirm the social, economic and cultural contexts of the images during the late Pleistocene,” says Porr.

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Snow leopards were among the animals hunted by DenisovansKlaus Honal / Alamy
Ancient humans known as Denisovans hunted a wide range of animals on the Tibetan plateau, including blue sheep, yaks and snow leopards. This varied diet enabled them to thrive in the high-altitude region for tens of thousands of years before the arrival of modern humans.
“Denisovans were behaviourally quite flexible,” says Frido Welker at the University of Copenhagen in Denmark. “They’re able to really adapt to the local environment and the species that are present there.”
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The Denisovans are one of the most mysterious groups of hominins with which we once shared the planet. They were first described in 2010, based on DNA extracted from a fragment of finger bone found in Denisova cave in the Altai mountains, Russia. It was the first time a hominin group had been identified solely based on DNA.
It is likely that Denisovans were once widespread in southern Asia because today many people in southern Asia and South-East Asia carry Denisovan DNA, indicating that Denisovans interbred with Homo sapiens tens of thousands of years ago. However, Denisova cave has only yielded teeth and other fragments. As a result, we don’t know much about what Denisovans looked like.
In 2019, researchers including Welker described a jawbone from Baishiya Karst cave in Xiahe in the north-east Tibetan plateau dated to 160,000 years ago. Protein from one of the teeth was identified as Denisovan.
The following year, another group found Denisovan DNA in the sediments of the cave. The DNA was variously 100,000, 60,000 and possibly 45,000 years old – implying that Denisovans lived there for over 100,000 years.
The Tibetan plateau is 4000 metres above sea level. The air is thin and it is cold and dry, making it a challenging place to live. To find out how the Denisovans survived for so long, Welker and his colleagues studied the animal bones from Baishiya Karst cave. By looking at the shapes of the bones and extracting telltale proteins, they identified 2005 out of 2567 bones or bone fragments.
The most numerous animals were blue sheep (Pseudois nayaur), or bharal. They and other sheep and goat relatives “make up around half of the assemblage”, says Welker. Other medium-sized plant-eaters included wild yak, Tibetan gazelles and red deer. There were also small animals like groove-toothed flying squirrels and porcupines. What’s more, there were some large carnivores, including spotted hyenas, wolves and snow leopards, plus some birds such as golden eagles.
Most of the bones seem to have been brought in by Denisovans: 19 per cent had clear evidence of this, such as cut marks made by stone tools, and less than 1 per cent showed signs – such as tooth marks – of being carried in by rodents or carnivores.
The setting of Baishiya Karst cave on the Tibetan plateauDongju Zhang’s group (Lanzhou University)
“This would be the second site where we can be absolutely certain that there are Denisovans present and that the associated assemblages specifically represent their behaviours,” says Samantha Brown at the University of Tübingen in Germany.
Other sites on the Tibetan plateau have stone tools but no hominin remains, so we don’t know who lived there. Further afield, a single molar tooth described in 2022 from Tam Ngu Hao 2 limestone cave in Laos has been tentatively identified as Denisovan.
We can’t draw too many inferences about Denisovans’ capabilities based on so few sites, says Brown. “However, we expect that Denisovans would once have been found as far north as Siberia and potentially as far south as [the islands of] South-East Asia. It could be that, as we find more of their sites, we really begin to see that Denisovans were highly adaptable.”
One of the bones from Baishiya Karst cave, a piece of rib, turned out to be another Denisovan. It was found in a layer of sediments dated to between 48,000 and 32,000 years ago – making it the youngest known Denisovan specimen. Welker says stone tools from Nwya Devu on the plateau are evidence that modern humans were also living there by 40,000 years ago – hinting that Denisovans and modern humans co-existed in the area.

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Skulls found in the banks of the river Thielle in Cornaux/Les Sauges in Switzerland are now stored at the Laténium Museum in HauteriveSchweizerischer Nationalfonds/Fonds national suisse
For decades, scientists have wondered about the history of 20 people, as well as a handful of farm animals, who seemingly drowned 2000 years ago in a Swiss river. One idea is that these individuals were sacrificed from a bridge, which later collapsed. But new evidence supports the notion that, for at least some of them, their demise – along with the bridge’s – was due to a natural disaster.
In 1965, archaeologists uncovered… More