Humans

A human bone from up to about 5900 years ago found inside the Cueva de los Marmoles cave in Granada, SpainJ.C. Vera Rodríguez, CC-BY 4.0
Prehistoric farmers and herders in southern Spain buried their dead in a large cave – but may have later cut them up to make tools and possibly eat their bone marrow.
Since 1934, scientists, amateur archaeologists and even tomb raiders have been exploring human skeletal remains left in a Granada cave, called Cueva de los Marmoles.
Within the 2500-square-metre cave – which has harboured multiple generations of bodies across three millennia – people have previously found a carefully carved human skull cup, a well-crafted tibia tool and dozens of other bone fragments. New evidence suggests that some remains may have been intentionally broken and scraped up to a year after the individuals died.Advertisement
The findings indicate that people may have been manipulating the deceased’s bones, after the cadavers had decayed slowly for some time in the cave’s cool, humid environment, says researcher Marco Milella at the University of Bern in Switzerland.
Milella, his co-lead researcher Rafael Martínez Sánchez at the University of Córdoba, Spain, and their colleagues went to the cave to collect further artefacts and investigate them using modern methods, such as advanced carbon dating, and hi-tech microscopic and scanning equipment.
They examined 411 bone fragments and 57 teeth that were unearthed in various zones of the cave, some of which they borrowed from a museum. They found that the remains were from at least a dozen human adults and children living in prehistoric agricultural societies. The findings suggest that people used the cave as a burial site during three distinct periods: 3900 to 3750 BC, 2600 to 2300 BC and 1400 to 1200 BC.
The team also found that while 3 per cent of the fragments had been gnawed by animals, nearly a third had been intentionally broken or cut with human tools. These fractures, scrapes and slices occurred when the bones were still “fresh” – probably up to a year after death, according to the researchers.

But the bones show no signs of having been forcefully separated from muscles or tendons. “This suggests that the human remains were already partially decomposed when manipulated, but with the bone still being relatively elastic,” says Millela. “This, in turn, points to action not performed shortly after the death of the individuals, but at least some months after death.”
Notable specimens include a skull – probably from a middle-aged man – that had been scraped with stone tools and fashioned into a bowl or cup, and a teenager’s shinbone that had been broken, polished and rounded into a sort of spatula, possibly for scraping other materials, such as leather. Several long bones had also been fractured and their insides scraped out, suggesting the marrow had been extracted for consumption, or possibly as part of a cultural practice of “cleaning the remains”, says Milella.
Lacking any evidence of violence, the remains are probably not the result of power struggles between different populations, he says. His team is planning to carry out DNA research that will compare the relationships among the individuals buried in the cave.

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A flint used to shape a log identified at the archaeological site Kalambo Falls in ZambiaLarry Barham, University of Liverpool
Ancient humans were building large wooden structures – possibly houses – almost half a million years ago. The discovery, the earliest evidence of wooden construction, suggests that some ancient communities were far less nomadic than we have assumed.
“These people were behaving in ways I hadn’t expected,” says Larry Barham at the University of Liverpool, UK. “It’s a disruptive discovery.”
Barham and his colleagues uncovered the evidence at Kalambo Falls, an archaeological site in Zambia. In 2019, they spent a month excavating a sandbar some 300 metres upstream of the falls.Advertisement
One of the first artefacts they found was a wooden tool, probably a digging stick. “The number of sites where wood is preserved is small,” says researcher Geoff Duller at Aberystwyth University, UK.
As they continued to dig, they made another discovery: a 1.4-metre-long log overlying an even larger log that was too big to fully excavate during their month-long project. They saw that the overlying log had been worked with tools to fashion a deep notch midway along its length. This allowed it to interlock with the underlying log at a 75-degree angle, creating a relatively sturdy joint. The researchers speculate that the two interlocking logs were once part of a larger wooden structure.
Duller then dated the artefacts using a technique called post-infrared infrared stimulated luminescence. This involves measuring the time since the mineral grains in the sand that surrounded the wood were last exposed to light prior to their burial. The mineral grains – and the artefacts they surround – were buried about 476,000 years ago, which implies that the wooden structure was built before our species evolved. The engineers therefore belonged to an earlier human species, possibly Homo heidelbergensis.
We already knew that ancient humans made use of wood. For instance, researchers have discovered 300,000-year-old wooden spears at a site in Germany, possibly made by H. heidelbergensis. “But those wooden implements are portable,” says Barham, which fits with the prevailing idea that early humans were always on the move. The large wooden structure at Kalambo Falls suggests to Barham that at least some early humans were staying put and choosing to enhance their environment. “They were investing in this place.”
“There’s something really exciting about this discovery that they were constructing and [they] had a real sense of the importance of place,” says Penny Bickle at the University of York, UK.
The ability to modify the local environment – sometimes called niche construction – isn’t uniquely human. Plenty of other species, such as beavers, do this too, but their techniques are far less sophisticated than those used at Kalambo Falls. “To my knowledge, [non-human] animals do not use tools to modify materials to create structures,” says Annemieke Milks at the University of Reading, UK.
The engineers at Kalambo Falls needed to produce sharp-edged stone tools from rocks, recognise they could use those tools to cut through wood and then work in groups to transport and modify that wood to produce a large structure. “It involved a lot of planning and I do think language was involved” says Barham.
However, it is difficult to say exactly what sort of wooden structure the logs once belonged to. Barham speculates it might have been a dwelling or maybe a wooden walkway raised above the wet floodplain designed to keep early humans, and their food, dry. Manuel Domínguez-Rodrigo at Rice University in Texas says that, while it may have been a structure or shelter, we can’t read too much into the function of just two pieces of wood.

In an accompanying opinion article, Milks says that the finding shows “when people started to structurally alter the planet for their own benefit”, arguably drawing a line between Kalambo Falls and today’s highly modified human environments.
But Barham thinks the story is more complicated. He says there were periods after the Kalambo Falls structure was built when humans were typically more mobile – meaning there isn’t a direct link between the apparently sedentary behaviour on show at Kalambo Falls and the sedentary human lifestyles of recent millennia.
Either way, the discovery should shift perceptions, says Barham, because it gives us a rare insight into just how important wood must have been to ancient humans. “We might need to rethink our labelling of the Stone Age,” he says. “Maybe it was more of a wood age.”

Journal references: Nature DOI: 10.1038/s41586-023-06557-9 and DOI: 10.1038/d41586-023-02858-1

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Rock art in Twyfelfontein, NamibiaAndreas Pastoors, CC-BY 4.0
Expert trackers have been able to identify the species depicted in around 400 animal footprints carved on rocks in Namibia during the Stone Age. In most cases, they were also able to identify the animal’s sex, the exact leg that made the print and whether the animal was an adult or not.
Numerous rock engravings thought to be up to  5000 years old have been found in sites around an area called Twyfelfontein in north-west Namibia. Many depict animal or human footprints, so Andreas Pastoors at the University of Erlangen-Nuremberg in Germany asked three trackers from Namibia, Tsamgao Ciqae, /Ui Kxunta and Thui Thao, to help his team study them. The three usually work for commercial hunters.
The trio identified the engraved animal tracks as depicting more than 40 species, ranging from rhinos and giraffes to aardvarks and porcupines. Around 60 of the tracks are those of birds, such as the secretary bird and the marabou stork.Advertisement

Most species depicted are still found in the area, but some – including blue wildebeest, buffalo, bushbucks and vervet monkeys – are found only in areas with more water, hundreds of kilometres away. Pastoors says there is no evidence the climate has changed in the region, so he thinks those who did the engravings must have travelled to where these animals lived.
The trackers also identified the sex depicted in around 100 engraved human footprints at the same sites, along with whether the footprints were meant to be those of an adult or child. The trackers identified the vast majority as depicting the footprints of children, with just 15 out of 106 being attributed to adults and three being unclear.
There is no way to check if the identifications made by the trackers definitely correspond with what the artists intended to depict. However, to experienced trackers the footprints of animals are just as distinct and recognisable as the animal itself, says Pastoors. Just as few people doubt that ancient carvings that look like lions really are of lions, so the trackers are confident in their identifications. “They always work together and make consensus decisions,” says Pastoors.
The team has considered numerous different possibilities for why the carvings of tracks were made, including that they were for teaching. But there is no clear evidence supporting any of the ideas. “We cannot understand what the depictions were made for, there’s no clue,” says Pastoors.
Similar carved tracks are found at many sites around the world, says Pastoors, who has also previously enlisted the same trackers to help analyse preserved human footprints on the floors of caves in Europe.

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From its origins on the Tibetan plateau, humans have transported cannabis across the planetAlexis Wnuk
Cannabis is everywhere: today, the plant grows on every continent except Antarctica. But that wasn’t always the case. So how did this “weed” come to take over the world?
Its success is due in large part to us. The evidence suggests that cannabis first evolved nearly 28 million years ago on the Tibetan plateau, after splitting off from the last common ancestor it shared with the hop plant. At first, early humans may have unwittingly spread it. By clearing vegetation for settlements and heaping food scraps in waste dumps, they gave cannabis what it needed to thrive: open, sunny areas with fertile soil. That is why some scientists refer to the plant as a weedy “camp follower”.
In time, humans came to appreciate the many uses of the cannabis plant, and it is believed to be one of the first plants we cultivated when we began farming around 12,000 years ago. The stalks could be dried to create fibres, the seeds could be eaten or used to make oil and the resin-coated bracts could have been used for their medicinal and mind-altering purposes (though evidence for the latter is much more recent).Advertisement
The plant’s utility enabled its spread and humans became the most important agent for its dispersal. Its seeds aren’t encased in tasty fruit, making them less attractive to animals, and they are round and heavy and lack wings that would let them hitch a ride on the wind.

From the Tibetan plateau, the plant spread across central and East Asia, with nomadic groups later carrying it into the Indian subcontinent, eastern Europe and the Middle East by about 2000 BC. As people began to cultivate cannabis for a broader range of uses, including its psychoactive effects, different varieties of the plant emerged. This gave rise to the two major types we know today – Cannabis sativa and Cannabis indica – though there is still debate over whether these are actually separate species or just different types of the same species.
By the Middle Ages, cannabis was grown across Europe, and Arab and Indian traders carried it into Africa and South-East Asia. Finally, colonial empires brought the plant to the Americas beginning in the 16th century.

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Porc-Epic cave in EthiopiaA. Herrero
A huge stash of reddish minerals from a cave in Ethiopia shows how Stone Age people gradually adapted their technologies and practices over a 4500-year period.
“It’s one of the rare sites where we can see a very precise evolution of this cultural feature through thousands of years,” says Daniela Rosso at the University of Valencia in Spain.
Rosso and her colleagues studied materials from Porc-Epic cave in Ethiopia. The cave first became known to scientists in the 1930s, and was thoroughly excavated in the 1970s. It was used by people in the Middle and Late Stone Age, between about 80,000 and 40,000 years ago, but the bulk of archaeological material dates from a 4500-year-long period about 40,000 years ago.Advertisement
This material included 4213 pieces of “ochre” – an umbrella term for minerals that are rich in iron and consequently have vivid colours, typically red. Prehistoric people often collected these minerals, but the original excavators of Porc-Epic did not study them. “This is the first time there is a systematic study of ochre use at this site,” says Rosso.

Rosso and her colleagues examined what the various pieces of ochre were made of. This changed over time: ochre from the beginning of the 4500-year period was typically high quality and rich in iron, while ochre from the end of the period was lower quality and had less iron. The later ochre was also coarse-grained, so instead of grinding it to powder the people tended to chip and cut it.
There are several possible explanations for the shift. One is that the people at Porc-Epic may have been using the ochre for different purposes as time went on, and chose different types accordingly.
The most famous use of ochre is as a pigment for artworks, but Rosso says it was probably sometimes used in utilitarian ways – for making adhesives, or as sunscreen, for example.
However, running counter to the idea that the shift was deliberate is evidence in a 2022 study by Rimtautas Dapschauskas at the University of Tübingen in Germany and his colleagues. They reviewed all known uses of ochre in Africa from 500,000 to 40,000 years ago. Dapschauskas says prehistoric people consistently sought out “fine-grained and blood-red materials”, which were the best for pigment as they could be ground to a very fine powder and produced vivid colours. “People really, really preferred those reddish colours,” he says.

So it may be that, as time passed, the people at Porc-Epic simply found it increasingly difficult to source the best-quality ochre. The team examined local geological deposits and found that the available ochres did not match those in the cave: they were often coarser-grained and had less iron. “Probably they had to go further away” to find the best ochre, Rosso says.
Why it became harder to get the high-quality ochre is unclear, says Dapschauskas, but it may be that the social situation changed: for instance, if the people at Porc-Epic relied on trade to secure good-quality ochre, then conflict with neighbouring groups might have led to shortages.
The study adds nuance to our understanding of technological stasis in the Stone Age, says Dapschauskas. “There’s a form of stability,” he says. “The cultural knowledge is transferred from generation to generation to generation.” But at the same time, the people were flexible and changed their practices over time. “They can really trace several thousands of years of behavioural change.”

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The limestone spheroids of ‘Ubeidiya, roughly the size of baseballs, seem to have been deliberately shapedLeore Grossman
An analysis of 150 round, baseball-sized stones found at a site where early humans lived 1.4 million years ago shows that they were intentionally knapped into spheres. This rules out the idea that they became round after being used as hammers, but doesn’t tell us why they were shaped.
“Unfortunately, we still can’t be confident about what they were used for,” says Antoine Muller at the Hebrew University of Jerusalem.

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Signs of ancient occupation at ‘Ubeidiya, in what is now northern Israel, were discovered in 1959. A few human bones and thousands of stone tools have been uncovered there. The site is thought to have been used by some of the first members of our ancestor species Homo erectus to move out of Africa.
The finds include nearly 600 stone balls made of flint, basalt and limestone. Similar discoveries have been made at many other early human sites dating as far back as 1.8 million years ago. The objects, known as spheroids, were made by knapping, but why this was done remains a mystery.
It has been suggested that they are a byproduct of the creation of other stone tools, or that they are stones deployed as hammers that became round as they were used rather than being deliberately shaped.
To test this idea, Muller and his colleagues scanned 150 limestone spheroids from ‘Ubeidiya, which are of varying degrees of roundness and around 8 centimetres in diameter, roughly the size of a baseball. They worked out the sequence of strikes responsible for each ball’s shape.

The researchers conclude that these spheroids required similar levels of skill and planning to make as hand axes, rather than being accidental creations. But the team can’t say if the same is true of any other spheroids, says Muller.
“Clearly, whoever made these objects was working hard to make them spheres,” says Andrew Wilson at Leeds Beckett University, UK, who in 2016 showed that the shape and weight of typical spheroids are suitable for throwing.
“To my mind, this certainly looks more like they were crafting projectiles than, say, hammers,” says Wilson. “I know from my work that these rocks would make good hunting weapons for a group of humans.”

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The shoes of a kneeling archer from the Terracotta ArmyDavid Davis Photoproductions RF/Alamy Stock Photo
Shoes worn by the warriors of the first emperor of China, famously depicted by the Terracotta Army, were surprisingly flexible and slip resistant, according to a reconstruction of the ancient footwear. The replicas help build a better picture of what Qin dynasty soldiers may have worn and how they might have aided them in battle.
The Terracotta Army was discovered in 1974 near Xi’an, China, and is formed of more than 8000 sculptures depicting the armies of the founder of … More

An ancestral population of humans was reduced to very low numbers, according to a genetic analysisThe Natural History Museum/Alamy
The population of our ancestors may have plummeted to as low as 1300 around 900,000 years ago, possibly as a result of our ancestral species splitting from other early humans.
That is the conclusion of an analysis of the variation in the genomes of living people by Haipeng Li at the Shanghai Institute of Nutrition and Health and his colleagues. However, while not dismissing the idea outright, independent experts say it isn’t supported by other lines of evidence.
Population bottlenecks occur when an existing population is reduced in size, for instance as a result of a catastrophe or when a small number of individuals leave one population to found a new one. This results in a sudden loss of genetic diversity.Advertisement
There have been numerous bottlenecks of varying scales as humans evolved and moved around the world. For instance, there was a major bottleneck when a small number of modern humans left Africa around 60,000 years ago, which is why there is still much more genetic diversity among people of African descent than in everyone living in the rest of the world combined. Much more recently, there was a series of bottlenecks as Polynesians settled island after island in the Pacific.
Past bottlenecks can be uncovered by looking for the reductions in genetic diversity they cause, but more ancient bottlenecks are harder to detect than recent ones. Li’s team developed a new method for estimating past changes in population size and applied it to the genomes of more than 3000 people from around the world.
According to the researchers’ findings, the population of our ancestors fell by 98 per cent to around 1280 “breeding individuals” around 930,000 years ago, and the population remained very low until around 815,000 years ago.
The early humans alive at this time have been assigned to a number of different species, including Homo heidelbergensis, Homo rhodesiensis, Homo antecessor and Homo bodoensis, and it is unclear which of these is our ancestor. There is also debate about whether they were indeed separate species.
Li and his colleagues think this bottleneck was most likely due to climate change, with global cooling around this time leading to severe drought in Africa and Eurasia. This “could explain the extreme scarcity of the available hominin fossil record in Africa and Eurasia” at the time, they write in their study.
Li says this is referring to previously published studies that have reported a gap at this time. “We didn’t find the fossil gap in this study,” he says. “Our findings actually explain the fossil gap.”
But in an accompanying paper, Nick Ashton at the British Museum and Chris Stringer at the Natural History Museum in London have put together a list of sites in Africa and Eurasia with evidence of continued human habitation during this time.
“The combined evidence, using several independent methods, seems strong,” says Ashton. “A global event seems unlikely as this would have affected populations in Eurasia as well as Africa.”
“The data of human presence that we marshalled suggest that its effects must have been limited in time and space,” says Stringer.
Li’s team also cites a paper by Brad Pillans at the Australian National University as evidence of drought in Africa and Eurasia at the time of the bottleneck. “We said nothing about aridity in Africa,” says Pillans. “So, in a way, the reference to our paper is not really correct.”

John Hawks at the University of Wisconsin, who wasn’t involved in the study, points to a paper from earlier this year suggesting that early humans in Africa were split into several distinct populations with only occasional migrations and mergers between them. It is possible that this population structure resulted in the appearance of a bottleneck, says Hawks.
Li’s team notes that the time of the bottleneck coincides with estimates for when two existing chromosomes fused to form chromosome 2. This is why humans have only 23 pairs of chromosomes rather than the 24 of chimpanzees and gorillas.
Another explanation for the bottleneck is that rather than there being a sudden reduction in population due to drastic climate change, it reflects a speciation event where a small number of individuals split away from other early humans after chromosome 2 evolved.
“The possible link to chromosome 2 is very interesting, and I think it may be true. But I would not assume that the bottleneck is real until we have a better understanding,” says Hawks. “It would be great to see more ancient DNA data that could get us back into this time period.”

Topics:human evolution More