Philippa Kaur

Becki Gill
It is fair to say that the family tree of ancient humans is not written in stone. Just take the case of the Denisovans, the enigmatic ancient humans who were, until recently, known only from a few fragments of bone. In June, molecular evidence indicated that a mystery skull from China was actually a Denisovan. These ancient people suddenly had a face.
Or did they? Anthropologist Christopher Bae at the University of Hawai’i at Mānoa is one of those who disagrees with the conclusions. He still feels the skull in question belongs where it was previously, that is, attributed to a species called Homo longi. In fact, Bae is at the heart of the tumultous debates about what our family tree ought to look like. In the past five years, he and his colleagues have suggested we add two ancient human species into the mix: Homo bodoensis and Homo juluensis.
Both suggestions caused controversy, partly because Bae and his colleagues wilfully broke the formal rules that govern how species are traditionally named. He is unrepentant, however, arguing that the rules themselves have become fossilised relics that make no allowance for removing species names that are now considered offensive, or for ensuring that names are easy for everyone to pronounce. He spoke to New Scientist about all this – and how his interest in human evolution was sparked by the mysteries in his own origin story.

Michael Marshall: What was it that first drew you into studying ancient humans?
Christopher Bae: The basic goal of palaeoanthropology is to reconstruct the past, even without all of the pieces of the puzzle. Being originally adopted, where the first year of my life is a complete blank, the field resonated with me. In my own case, I was born in Korea, then I was abandoned when I was about a year old, and I lived in an orphanage for about six months before being adopted by an American family.

When I was an undergraduate student, I was able to go to Korea for the first time on an exchange programme, and during that trip I went to the adoption agency where I came from. I asked the manager whether there was any chance that I could actually find my biological parents. They said, to be honest, your Korean name is not real and your date of birth is not real. You shouldn’t even bother trying. There’s absolutely no chance. I kind of gave up at that time.
So I was interested in my own roots and I couldn’t figure out how to find them. But then I took an introduction to biological anthropology course, and I found a field where I could actually explore origins. It’s kind of like building my own origins.
Two species that often pop up in discussions about our direct ancestors are Homo heidelbergensis and Homo rhodesiensis. But in 2021, you were part of a team that proposed replacing them both with a new species named H. bodoensis. Why?
My colleague, Mirjana Roksandic [at the University of Winnipeg, Canada], and I organised a session at a 2019 anthropology conference focused on the H. heidelbergensis question. There was general agreement that H. heidelbergensis is what we call a “wastebasket taxon” because anything from the Chibanian Age [775,000 to 130,000 years ago] that doesn’t clearly belong to Homo erectus, Homo neanderthalensis or Homo sapiens tended to be assigned to it.

So what happens to the H. heidelbergensis fossils that do constitute a distinct group of hominins, do they get a new name?
If we get rid of H. heidelbergensis, the next name, based on the rules of priority, is H. rhodesiensis. But that species was named after Northern Rhodesia, the old name of present-day Zambia, which itself was named after Cecil Rhodes. Now, do we really want to name the potential ancestor of modern humans after a known colonialist like Rhodes? So, when we were putting that paper together, we said, you know what, we’ll come up with a new name, and we’ll name it after Bodo [a 600,000-year-old skull from a site in Ethiopia].

What was the reaction to your paper?
When it went out for review, half the reviewers said, this has got to be published because we have to have this discussion out there. The other half of the reviewers said, this is ultimate garbage, it should not be published. Not surprisingly, there was a back-and-forth as soon as the paper came out.
Is there any emerging consensus yet?
We had a workshop in 2023 in Novi Sad in Serbia. We had about 16 or 17 palaeoanthropologists working on this topic. We all agreed that H. heidelbergensis has become a wastebasket taxon. The other major conclusion was that H. rhodesiensis should be removed from circulation because of Rhodes’s colonial history. In fact, only one of the palaeoanthropologists in attendance thought rhodesiensis was not problematic.
The Xujiayao site in northern ChinaChristopher J Bae
It is the International Commission on Zoological Nomenclature (ICZN) that ultimately judges cases like this. Has it responded to your H. bodoensis argument?
The ICZN published a paper in the Zoological Journal of the Linnaean Society in 2023, a pre-emptive strike, and it said: We’re not going to remove any names from circulation where there may be ethical issues. We actually ended up going down a rabbit hole as a result of this, and challenging the ICZN. [Editor’s note: The ICZN’s 2023 statement recognised that scientific names might cause offence, but said it is outside the scope of the commission to assess the morality of persons honoured in eponyms. It also emphasised the importance of zoologists following its code of ethics when naming new species.]
Are species names really important enough to fight over?
Yes and no. For instance, there’s a beetle from a few caves in Slovenia. In the 1930s, an Austrian entomologist [Oskar Scheibel] said, I’m going to name this as a new species, after Adolf Hitler. Nowadays, the beetle [Anophthalmus hitleri] is a hot product as a keepsake. On the black market, people are selling them because a lot of neo-Nazis want to collect them. It’s eventually going to lead to the extinction of these poor innocent beetles, who haven’t done anything to bother anybody.
What’s the alternative?
I would say, talk with your local collaborators and find a species name that would be acceptable for them, because they’re the ones who are going to have to deal with it and live with it on a regular basis. I would hope that we stop using people’s names to name species or we’ll continue to run into problems down the road. I think that’s the direction that we’re going to go – and change is in the air. The ICZN is trying to change how they can attract members from the Global South and give them more of a voice. And some other major associations such as the American Ornithological Society have recently voted to remove egregious species names from the biological organisms they study.

You fell foul of the ICZN rulebook again last year, regarding some ancient human fossils from a site in northern China called Xujiayao. What’s the story there?
Researchers found a bunch of different hominin fossils at that site in the 1970s representing more than 10 individuals, but the fossils were all separate pieces. My colleagues and I, including Xiujie Wu [at the Chinese Academy of Sciences], worked on these fossils. Wu actually did a virtual reconstruction of the posterior part of one skull. And when we looked at it, we said, wow, this looks really, really different from other similar-aged hominins.
What sort of differences are we talking about?
Size and shape differences. Our average cranial capacity is about 1300 to 1500 cubic centimetres. These guys have a cranial capacity between 1700 cm³ and 1800 cm³ – so much, much larger than your average human. Furthermore, based on a shape analysis, it was clear that the Xujiayao fossils – and fossils from a nearby site named Xuchang – consistently fell away from the other fossils and grouped together. That’s what led us to naming a new species.
Bae examines a human fossil found in Serbia that may belong to Homo bodoensisChristopher J. Bae
But the name you chose was controversial. Can you explain why?
Where species names actually come from is quite fascinating. In this case, we could have named it after Xujiayao – which is the type site – and then added “-ensis” at the end, making it Homo xujiayaoensis. This follows the ICZN rules.
And in Latin, that means “Homo belonging to Xujiayao”. But you didn’t like that option?
The problem is, only people who speak Chinese will be able to pronounce it, let alone spell it correctly. Names actually mean something. You need to be able to pronounce and spell them. So we came up with “julu”, which literally means “big head”.
If we follow the ICZN rules, though, then we are required to add an “i” at the end, making “Homo jului”. However, in our view, again, people would not be pronouncing it correctly unless they understood Chinese. Some people might say “julu-eye”, others would say “julu-ee”. This is why we chose Homo juluensis.
How does your new species relate to the mysterious Denisovan humans, who lived in what is now East Asia during the Stone Age?
If you look at the second molars from the Denisova cave in Siberia and the second molars from Xujiayao, they look almost exactly the same. You could actually take the Xujiayao molar and put it in Denisova, and then take the Denisova molar and put it in Xujiayao, and few people would know the difference.

But earlier this year, another group of researchers linked those same Denisovan fossils to a different ancient species from China called Homo longi – and that idea seems to have gone down well with many researchers.
In China, actually, most palaeo people agree with our H. juluensis argument. A lot of Westerners that are familiar with the Chinese record also tend to agree.
But what about evidence from the skull that appeared in June? Researchers extracted ancient proteins from a skull attributed to H. longi and found a match with proteins extracted from known Denisovan fossils.
When you talk to most geneticists, they say that you could probably discount the protein analysis for species-level identification. You can get at a broader level, like a cat and a dog, but it’s really hard to identify distinctions at a finer level.
Replica of a Denisovan molar, originally found in Denisova Cave in 2000Thilo Parg CC BY-SA 3.0
Would you still accept H. longi as a valid species?
Oh yeah, I actually like H. longi and the fossils assigned to it. The debate revolves around what other fossils, if any, should be assigned to longi or whether some of these other fossils should be assigned to juluensis. It is interesting nowadays that the longi supporters seem to be trying to lump everything into longi, despite clear morphological variation in the Chinese fossils.
I’ve seen a few strongly negative reactions from other palaeoanthropologists to some of your research. How do you and your colleagues respond to that?
At this point in our careers, we’ve developed thick skin.

Topics: More

Illustration of a teenage girl who is the offspring of a Neanderthal mother and Denisovan fatherJOHN BAVARO FINE ART/SCIENCE PHOTO LIBRARY
For only the second time, researchers have obtained the full genome of a Denisovan, a group of ancient humans who lived in Asia. The DNA was extracted from a single 200,000-year-old tooth found in a Siberian cave.

The genome reveals that there were at least three populations of Denisovans, with different histories. It also shows that early Denisovans interbred with an unidentified group of ancient humans – and with a hitherto-unknown population of Neanderthals.
“This is a bombshell paper,” says David Reich at Harvard University.
“This study really expanded my understanding of the universe of the Denisovans,” says Samantha Brown at the National Research Center on Human Evolution in Spain.
Denisovans were the first ancient humans to be described using just DNA. A sliver of finger bone from Denisova cave in Siberia held DNA unlike that of either modern humans or the Neanderthals from western Eurasia. The genome revealed that Denisovans interbred with modern humans: people in South-East Asia, including the Philippines and Papua New Guinea, carry Denisovan DNA.

Since the initial reports in 2010, researchers have identified a handful of other Denisovans, all from East Asia. In June, a skull from Harbin, China, was identified as a Denisovan using molecular evidence, revealing for the first time what a Denisovan face looked like. However, while several specimens have yielded fragments of DNA, the original specimen has been the only one to yield a high-quality genome.
Researchers led by Stéphane Peyrégne at the Max Planck Institute for Evolutionary Anthropology in Germany have now added a second. (Peyrégne declined to be interviewed because the study hasn’t yet been peer-reviewed.)
The team found a single molar tooth, belonging to a male Denisovan, in Denisova cave in 2020 and sequenced an entire genome from the preserved DNA.
Based on the number of mutations in the genome and comparisons to other ancient humans, the team estimated that the individual lived about 205,000 years ago. In line with this, the sediments in which the tooth was found were dated to 170,000-200,000 years ago. In contrast, the other high-quality genome is from a Denisovan who lived 55,000-75,000 years ago, meaning that the new genome reveals a much earlier stage of Denisovan history.

Based on comparisons with other remains from Denisova cave, the team says there seem to have been at least three discrete Denisovan populations. The oldest group included the male whose tooth was analysed. A second group replaced this older population at Denisova cave, thousands of years later.
“Understanding how early Denisovans were replaced by later Denisovans highlights a significant human event,” says Qiaomei Fu at the Institute of Vertebrate Paleontology and Paleoanthropology in China.
The third group, not represented at the cave, interbred with modern humans, based on DNA testing. In other words, all the Denisovan DNA in modern humans comes from a population of Denisovans that we know little or nothing about.
The new genome reveals that Denisovans repeatedly interbred with Neanderthals, who sometimes lived in or near Denisova cave. Crucially, the genome includes traces of a Neanderthal population that lived 7000-13,000 years before the male Denisovan. These traces don’t match any known Neanderthal genome, suggesting the Denisovans interbred with a Neanderthal group that has not yet been sequenced.
The Denisovans also seem to have interbred with an unidentified group of ancient humans, one that had evolved independently of Denisovans and modern humans for hundreds of thousands of years. One possibility is Homo erectus, which, based on current knowledge, was the first hominin to migrate outside of Africa, living as far afield as Java, Indonesia. However, no DNA has yet been recovered from H. erectus, so we can’t be sure.
“It’s endlessly fascinating that we keep discovering these new populations,” says Brown.

Topics: More

The mummified remains of a boy buried in a copper box between 1617 and 1814Annamaria Alabiso
An adolescent boy buried around three centuries ago in a copper box in northern Italy has become the only near-complete green mummy ever known.
Other ancient body parts have been partially mummified or turned green after burial with copper or bronze objects, like the green, mummified hand of a newborn baby clutching a copper coin, buried in a ceramic pot in medieval Hungary.

The Italian mummy, however, is complete except for the feet. Apart from its left leg, it is almost entirely green from skin to bone.
The mummy was discovered in the basement of an ancient villa in Bologna in 1987 and sent for forensic analysis at the University of Bologna. Medical examiners determined it was the body of a boy aged 12 to 14. Since then, it has been carefully stored at the university.
Annamaria Alabiso, a conservation scientist at the University of Rome Tor Vergata, was part of an investigation of the mummy by a wide array of specialists, including geneticists, anthropologists, radiologists, mathematicians, physicists and computer scientists. “It was a very remarkable multidisciplinary collaboration,” she says.

The researchers ran multiple in-depth chemical and physical analyses of the mummy. Radiocarbon dating placed the boy’s death to between 1617 and 1814, says Alabiso, and the mummy shows no clear signs of trauma or disease.
Copper helped preserve the hard and soft tissues – as expected, given its known antimicrobial properties, says Alabiso. But it also reacted with acids that leaked out of the body and corroded the box. This created copper corrosion products that interacted with chemical compounds in the bone. Little by little, copper ions replaced calcium in the boy’s skeleton, solidifying the bone structure in the long term while tinting the affected areas various shades of green.
As for the skin, it was covered by a crusty film of copper corrosion products called patina – the pale-green coating that develops on copper and bronze statues. The patina developed when copper reacted with water and carbon dioxide as the body broke down, says Alabiso.
“This completely changes our point of view on the role of heavy metals, as their effects on preservation are more complex than we might expect,” she says.

The bottom of the box eventually cracked open – possibly due to the acid – letting the liquid spill out so that the body stayed in a cool, dry chamber with little oxygen, which slowed decomposition. The boy’s feet might have detached and got lost at this time, says Alabiso.
“It was just a very emotional experience for me to work with these unique human remains,” she says.
Giulia Gallo at the Collège de France in Paris recently saw images of the mummy for the first time – and was delighted. “Oh wow, it’s incredible!” she says. “It’s so beautiful! This whole case study is quite fascinating.”
Gallo says the researchers have done an excellent job of exploring all the physical and chemical processes leading to the body’s mummification and colour changes. “The evidence strongly substantiates their argument concerning both the preservation and coloration of the tissue and bone.”

Historic Herculaneum – Uncovering Vesuvius, Pompeii and ancient Naples

Embark on a captivating journey where history and archaeology come to life through Mount Vesuvius and the ruins of Pompeii and Herculaneum.

Find out more

Topics:archaeology More

Neanderthals may have used ochre crayons to draw on cave wallsGorodenkoff/Getty Images
A remarkable yellow crayon unearthed in Crimea, still sharp after more than 40,000 years, indicates that painting lines on objects was part of Neanderthal culture. This discovery is the firmest evidence yet that some Neanderthal groups used coloured pigments in symbolic ways – behaviour once regarded as the sole domain of our species.
“It’s really exciting. It adds a new facet to what we know about symbolic use of colour,” says Emma Pomeroy at the University of Cambridge, who wasn’t involved with the research.

The use of ochre – an iron-rich mineral with red, yellow or orange hues – has ancient roots, dating back at least 400,000 years in Europe and Africa. Bits of ochre are found at many Neanderthal sites, where they seem to have been used for practical purposes such as tanning clothing and as fire accelerants, as well as sometimes smeared on shell beads.
Neanderthals may have also used ochre to decorate their bodies, clothing and other surfaces, but such traces have long since disappeared. To investigate further, Francesco d’Errico at the University of Bordeaux, France, and his colleagues carried out a detailed analysis of ochre pieces found at Neanderthal sites in Crimea, Ukraine. By studying how ochre pieces were modified by Neanderthals, as well as performing a microscopic analysis of how they became worn down, the researchers could build a picture of how the objects were used.
The most compelling of these ochre objects was a yellow one that was at least 42,000 years old and had been ground and scraped into a crayon-like shape about 5 to 6 centimetres long. Detailed analysis shows that the tip had been worn down through use, then resharpened, indicating that it was reused over time as an implement to make marks.

“It was a tool that had been curated and reshaped several times, which makes it very special,” says d’Errico. “It’s not just a crayon by shape. It’s a crayon because it was used as a crayon. It’s something that may have been used on skin or a rock to make a line – the reflection, perhaps, of an artistic activity.”
The tip of an ochre fragment that has been used as a crayon and then resharpenedd’Errico et al., Sci. Adv. 11, eadx4722
April Nowell at the University of Victoria in Canada, who wasn’t involved with the research, concurs. “You only maintain a point on a crayon if you want to make precise lines or designs,” she says.
The research team also identified another more ancient broken crayon, perhaps 70,000 years old, made from red ochre.

“It tells us so much just from those small bits of ochre,” says Pomeroy. “It’s that little bit of humanity that we can relate to. It really brings those individuals into touching distance.”
The Crimean crayon discoveries add to the small but growing body of evidence indicating the artistic talents of Neanderthals, such as 57,000-year-old finger carvings on a cave wall in France and mysterious circles crafted from stalagmites 175,000 years ago in another French cave.
They also lend weight to the idea that symbolic behaviour has very deep roots in our evolutionary past, rather than being a capacity that developed relatively recently only in Homo sapiens. “The underlying cognitive ability for symbolic behavior is undoubtedly shared by the last common ancestor of Homo sapiens, Denisovans and Neanderthals more than 700,000 years ago,” says Nowell.

Ancient caves, human origins: Northern Spain

Discover some of the world’s oldest known cave paintings in this idyllic part of Northern Spain. Travel back 40,000 years to explore how our ancestors lived, played and worked. From ancient Paleolithic art to awe-inspiring geological formations, each cave tells a unique story that transcends time.

Find out more

Topics:Neanderthals More

Simon Pemberton
Disease historians have a problem. While examining samples of ancient human DNA, geneticists have come across genes belonging to the plague bacterium, Yersinia pestis, revealing that it ravaged Eurasia 5000 years ago. That’s nearly 3500 years before the “first plague”, also known as the Justinian plague, after the Roman emperor of the day. What to call this newly discovered prequel?
The current favourite, the Late Neolithic-Bronze Age (LNBA) plague, is a bit of a mouthful. But the scientists have more to worry about. Their chance discovery is another nail in the coffin of a long-held idea about when and why humanity acquired many of the contagious diseases that now afflict us. Of late, they have uncovered a rogue’s gallery of prehistoric horrors in samples taken from ancient humans. These so-called zoonotic diseases bothered animals before they bothered people, so were thought to have jumped the species barrier after humans invented agriculture, around 12,000 years ago. But as geneticists can peer further back into the past, they are finding that in many cases the leap occurred much later – with major outbreaks happening in Europe, you’ve guessed it, around 5000 years ago.
As well as upending old ideas about disease evolution, the discovery has forced a rethink of a pivotal period in prehistory. How were diseases spreading at that time? Did the pathogens have the same effects as they do now? And might plague itself have ushered in the Bronze Age, laying the foundations of European civilisation? It’s exciting stuff, says archaeogeneticist Megan Michel at Harvard University, given that a decade ago, “we didn’t even know this plague existed”.

The reconstruction of ancient disease landscapes has been a huge collaborative effort, but a group at the University of Copenhagen in Denmark has had a leading role. They began routinely screening ancient human remains for known pathogens about 15 years ago, having unexpectedly found microbial DNA in human samples. Armed with radiocarbon dates and information about how people in prehistoric cemeteries were related to each other, they could start to build a picture of the cultural and economic context in which the diseases spread. They could also track the evolution of pathogens over time – and investigate how the human immune system adapted in turn.
This approach has generated a quickfire sequence of important findings, including the discovery of pathogens that cause typhoid, hepatitis B, syphilis and smallpox in historical human populations – and culminated this July in the publication of a study led by population geneticist Martin Sikora, a member of the Copenhagen group. His team re-analysed around 1300 human samples spanning more than 35,000 years in Eurasia. All the DNA came from teeth, which preserve blood-borne pathogens because they have their own blood supply in life. Among the pathogens the researchers found were Y. pestis and the bacteria that cause leprosy and leptospirosis, or Weil’s disease. To their surprise, nearly 3 per cent of samples tested positive for another pathogen, Borrelia recurrentis, the causative agent of the now-rare relapsing fever – a relative of Lyme disease characterised, as its name would suggest, by recurring fever and blinding headaches.

The team also looked at trends over time. These revealed that until about 6500 years ago, the vast majority of microbes in the teeth of Eurasians belonged to the oral microbiome – the diverse, usually harmless or even beneficial community of organisms that inhabits the mouth. The first zoonotic pathogens, including plague, became detectable at that date, but only at very low levels. It wasn’t until around 5000 years ago that there was a spike in infections from Y. pestis and other major pathogens.
Arrival of the Yamnaya
This also happens to be the date that nomadic herders called the Yamnaya began arriving in Europe from the steppe, a vast expanse of grasslands and savannas spread across much of Eurasia, bringing new ideas and new languages. Coincidence? The researchers think not. Those herders had an exceptionally high burden of infectious disease. It isn’t clear why, but it was probably linked to their lifestyle. They kept much larger herds than static farmers – of sheep, goats, horses and cattle – and they lived with their animals around the clock. Their diet consisted mainly of meat and milk. “A lot of zoonoses can be transmitted through undercooked meat, but also through milk: brucellosis, listeriosis, bovine tuberculosis, to name just a few,” says infectious disease expert Astrid Iversen at the University of Oxford.
Plague doctors treated victims of bubonic plague during outbreaks in EuropeScience History Images/Alamy
Other findings appear to corroborate this hunch. For instance, by tracing how the genome of plague bacteria changed over time, archaeogeneticist Pooja Swali at University College London has been able to show that 4000-year-old cases of plague – which were the oldest known in Britain when she documented them in 2023 – were caused by strains related to those carried earlier out of the steppe. She could effectively see the disease moving from east to west.
Then there is relapsing fever. Earlier this year, Swali reported that B. recurrentis became specialised to humans in a window centring on 5000 years ago. Before that, the bacterium infected a range of mammals via the tick, its intermediate host, but then it swapped this out for the human body louse. Swali speculates this had to do with wool clothing, another innovation – besides metal tools – brought to Europe by the steppe nomads. B. recurrentis underwent a major reduction of its genome at that time, which could reflect adaptation to a new host – one that flourished in wool garments. “Maybe this massive reduction in genome meant that it became trapped in lice,” she says.
Meanwhile, French researchers have shown that the immune system of Europeans began adapting to infectious diseases like these around 6000 years ago, with the bulk of immunity-related genetic variants appearing around 4500 years ago. “All these pieces fit really nicely together,” says Sikora.
But there’s one piece that doesn’t fit so well. Sikora’s July paper cites two cases of plague in Orkney, off the north coast of Scotland, that predate the arrival of people with steppe ancestry in Britain by at least 500 years. What’s more, last year, another member of the Copenhagen group, Frederik Seersholm, described three outbreaks of plague over six generations of Neolithic Swedish farmers that occurred around 5000 years ago. Those farmers carried no steppe ancestry, indicating that they had yet to interbreed with – perhaps even to meet – these populations of eastern origin. A new study from Seersholm and Ruairidh Macleod at UCL, which has yet to be peer-reviewed, describes the oldest instances of plague in the world recorded to date, from around 3500 BC, which proved fatal to hunter-gatherers living near Siberia’s Lake Baikal, east of the Yamnaya’s point of departure towards the west.
Such cases have persuaded most people that plague was geographically widespread before the nomads arrived. One idea is that the LNBA plague got its foothold in the mega-settlements of the Trypillia culture of present-day Ukraine, beginning around 6000 years ago, and then spread through trade networks. Archaeogeneticist Nicolás Rascovan at the Pasteur Institute in Paris, who suggested this possibility in 2019, says his hypothesis remains on the table, though he admits it is difficult to test because almost no Trypillian burials have been found. Others are sceptical. A team led by anthropologist Alex Bentley at the University of Tennessee, Knoxville, has shown that the clustered layout of Trypillian megasites could have introduced effective firebreaks to contagion. Besides, the Baikal cases indicate plague was a problem for hunter-gatherers from an early date.
Plague without the fleas
What the disease was like back then is also unclear, but there is no doubt it could kill. “Whether it was as highly transmissible as the Black Death, I’d be more cautious,” says Sikora. It is unethical to try to revive ancient plague strains in the lab, but you can get a rough idea by comparing ancient plague genomes with later strains that have known clinical outcomes. Such analysis has revealed that LNBA strains lacked a genetic variant that allowed the bacterium to survive in the flea gut, leading researchers to conclude that they probably weren’t transmitted by flea bites, as the Black Death was in the 14th century.
Human body lice proliferated around 5000 years ago and became a vector for relapsing feverMARTIN OEGGERLI/SCIENCE PHOTO LIBRARY
There are many other ways plague could have spread in the Late Neolithic, though. Macleod and Seersholm suggest it was airborne and spread through coughing. But we can’t assume it was capable of human-to-human transmission. Another possibility is that outbreaks were caused by people sharing feasts of undercooked, infected meat – in which case, each outbreak was an animal-to-human spillover event that probably fizzled out quickly. Plague has many animal reservoirs, including sheep, dogs and rodents, and researchers know very little about how prevalent it was in other species in the Late Neolithic, or how it evolved in them. “What’s missing is this huge piece of the puzzle – the animals,” says Swali.
Amid all the uncertainty, arguably the most burning question is whether the plague caused the so-called Neolithic decline, a dramatic fall in the population of western Eurasia. If so, it might also have ushered in the Bronze Age in that part of the world, a cultural revolution that introduced a more hierarchical and warlike social model – perhaps by clearing the way for those nomadic steppe herders who organised themselves in that way.
The Neolithic decline
Neolithic farmers lived in denser, more permanent settlements than herders or hunter-gatherers, and lots of people living in proximity certainly lend themselves to contagion. Seersholm thinks his study of Swedish farmers supports the idea that plague caused their decline. However, archaeological evidence – the thinning of the farmers’ cultural footprint, signs of violence and the regrowth of forests – suggests it began around 7000 years ago, 500 years before the first zoonoses appeared in Europe. “I retain my scepticism that plague is responsible for this population downturn,” says archaeologist Stephen Shennan at UCL. He thinks the root cause was an agricultural crisis – shrinking crop yields related to a cooling climate. Nevertheless, he says he might have to change his mind if earlier plague cases come to light.
That is possible. Geneticists are confident that the prehistoric prevalence of infectious disease was much higher than is detectable, in part because a disease can kill without showing up in the patient’s blood. This is the case for tuberculosis, for example, but also for the pneumonic form of plague, which infects the lungs. RNA viruses such as flu and coronaviruses aren’t yet detectable, either. Researchers are already searching for more evidence that Neolithic communities cratered as a direct consequence of plague. And one of them, archaeologist Kristian Kristiansen at the University of Copenhagen, thinks they will find it.
Whether or not the LNBA plague caused the decline, it could have exacerbated it – especially after the arrival of the Yamnaya. Kristiansen doubts that their expansion into Europe was driven by plague – he prefers the theory that population growth forced them to go in search of new pastures. But, he says, they might have picked up plague en route, to which their lifestyle offered them at least partial immunity, and then spread those strains far and wide. Their contact networks extended much further than those of farmers. “You can see it clearly in the human DNA,” says bioarchaeologist Thomas Booth at London’s Francis Crick Institute. “Suddenly, after 3000 BC, there are biological ties stretching right across Eurasia where previously they had been more confined to smaller regional clusters.”And, of course, plague wasn’t the only disease to have a major impact. “One of the big takeaways for me, from the Sikora paper, is that around 10 per cent of the tested remains had positive evidence for a major infection at time of death,” says one co-author, evolutionary biologist Evan Irving-Pease at the University of Copenhagen. “The level of evolutionary pressure that would have exerted on ancient human populations is really quite substantial.” He and others believe that, in today’s more hygienic environment, variants of genes that were selected because they protected our ancestors from zoonotic disease predispose us to a different threat – autoimmune diseases such as multiple sclerosis (MS).
Yamnaya steppe nomads spread across Europe at just the time when animal-borne diseases proliferatedPiotr Włodarczak
Last year, with William Barrie at the University of Cambridge and others, Irving-Pease reported that a major genetic risk factor for MS tracks with steppe ancestry in Europe, being highest in the north of the region and lowest in the south. MS can be triggered by infection with the common Epstein-Barr virus today, but a different dangerous pathogen, prevalent in the Bronze Age, might initially have driven selection for that risk factor. Irving-Pease doesn’t know what it was, but with Iversen and others, he is hot on its trail.
And the Late Neolithic disease surge may have shaped more than the immune system. Before then, Europeans didn’t practise dairying and were mostly lactose intolerant – unable to digest the sugar in milk. One surprising discovery is that the Yamnaya were, too: they probably consumed milk in fermented form – as yoghurt, kefir or cheese – and unwittingly recruited free-living bacteria to digest the lactose for them. So they didn’t bring Europeans the genes that allow us to do this for ourselves. Instead, research hints, these variants may have increased in frequency when bouts of disease and associated famines forced Neolithic farmers to drink milk to survive.

Disentangling these complex biological and cultural interactions has implications for the future. Researchers may be close to uncovering the origins of MS, for example, but they can’t yet explain why it is becoming more prevalent over time. And zoonoses continue to pose a threat, accounting for an estimated three-quarters of emerging human diseases, including covid-19 – often because of our industrial-scale farming practices, destruction of forests and alteration of the climate. Understanding how they shaped us in the past will help us predict what lies ahead – and, potentially, to intervene with the powerful tools of modern medicine.
For the moment, though, it is the prospect of shedding light on our past that excites researchers most. “We can start to ask more interesting questions about the role of pathogens in human prehistory,” says Michel. Infectious disease has been called “the loudest silence in the archaeological record”. Finally, we are dialing up the volume.

Topics: More

A model of a Neanderthal womanJoe McNally/Getty
Modern humans may indeed have wiped out Neanderthals – but not through war or murder alone. A new study suggests that when the two species interbred, a slow-acting genetic incompatibility increased the risk of pregnancy failure in hybrid mothers. A similar mismatch between mothers and fetuses may also help explain a subset of pregnancies that fail today.
We know from genetic studies that there was sustained interbreeding between Homo sapiens and Neanderthals between approximately 50,000 and 45,000 years ago. The Neanderthals went extinct around 41,000 years ago, but some of their DNA has persisted in modern humans with non-African ancestry, making up around 1 to 2 per cent of the genome.

But mysteriously, none of the mitochondrial DNA in modern humans is derived from Neanderthals. This form of DNA is carried by egg cells but not sperm, so it is always inherited from the mother.
Patrick Eppenberger at the University of Zurich, Switzerland, and his colleagues have proposed a possible explanation for this. They suggest that women with Neanderthal and H. sapiens parents would have had a higher risk of pregnancy failure because of a mismatch between their genes and those of their fetus.
Neanderthals and H. sapiens had different versions of PIEZO1, a gene critical to oxygen transport in the blood. The researchers analysed modern human and Neanderthal DNA and modelled the differences in the PIEZO1 protein to understand how the two variants would have interacted. They also studied human red blood cells in the lab, using a chemical treatment to simulate the effect of the Neanderthal variant.

They found that the Neanderthal variant, V1, results in red blood cells that bind oxygen more strongly compared with the H. sapiens variant, V2. V1 is dominant, so a person who inherited both V1 and V2 would have red blood cells with this high oxygen affinity.
This means that a fetus resulting from Neanderthals and H. sapiens interbreeding could have developed healthily in either a Neanderthal or H. sapiens mother. But according to the study, problems would have arisen in the next generation. A hybrid mother with V1 and V2 carrying a fetus with two copies of V2 would have had higher oxygen affinity than her fetus, so she would deliver less oxygen across the placenta. This might impair the growth of the fetus and increase the risk of pregnancy loss.
Eppenberger and his colleagues declined to be interviewed, but in a paper they argue that this incompatibility would have led to the Neanderthal population experiencing a drain on its reproductive output. “Over millennia of coexistence, even low levels of gene flow from modern humans into Neanderthal populations could have introduced a gradual reproductive disadvantage, compounding over generations,” they write.
It wouldn’t be such a problem for the H. sapiens population because it was much larger, the team suggests. Neanderthal DNA could spread through the population via fathers, but the V1 variant would quickly be eliminated by natural selection. This could explain why Neanderthal nuclear DNA persisted in modern humans, while mitochondrial DNA, inherited only through mothers, didn’t.
Although not derived from Neanderthal DNA, the researchers also note that some mutations in PIEZO1 with a similar effect do occur today, and could cause some cases of unexplained pregnancy loss through a similar mismatch between mother and fetus.

Sally Wasef at the Queensland University of Technology in Brisbane, Australia, says the discovery of the delayed, second-generation incompatibility is a “good insight”. “Even a minor hit to reproduction can push small groups below replacement, which can start a slide in numbers and, in fragile settings, an extinction spiral,” she says.
“That being said, I would treat this finding as one piece of the puzzle rather than the whole story,” she says. “The effect is likely to be modest and to add to other ecological and social pressures.”
Laurits Skov at the University of Copenhagen in Denmark says there were probably multiple factors involved in the Neanderthals’ demise, including changes in climate, the arrival of modern humans, the small community size of Neanderthals, the introduction of new diseases and genetic incompatibilities.
Skov also says he would be surprised if this difference in oxygen affinity were determined by a single mutation in the PIEZO1 gene, as the researchers suggest.
“I think more work is needed to conclusively say what the impact of this particular mutation is – and what happens when the mother and fetus have different configurations,” he says. “Or what role, if any, did this mutation play in the extinction of Neanderthals.”

Neanderthals, ancient humans and cave art: France

Embark on a captivating journey through time as you explore key Neanderthal and Upper Palaeolithic sites of southern France, from Bordeaux to Montpellier, with New Scientist’s Kate Douglas.

Find out more

Topics: More