THE Rub’ al-Khali is both desert and deserted – a landscape of reddish sand dunes that stretches as far as the eye can see. This hyper-arid region in the south-east of the Arabian peninsula is approximately the size of France. Parts of it often . Almost nobody lives there; its name means “empty quarter”.
The rest of Arabia is less environmentally extreme, but still a very tough place to live without air conditioning and other recent technologies. However, the peninsula wasn’t always so parched. , it was wet enough for there to have been many lakes. The same was true at intervals throughout the past million years, when rivers criss-crossed Arabia, forming green corridors where lush vegetation and wildlife flourished amid the sand dunes. For much of recent geological time, the peninsula was at least partly green.
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Arabia’s verdant past is no mere factoid: it suggests that the region was habitable at times in the distant past. That realisation has prompted archaeologists to start looking for evidence of occupation by humans, their ancestors and their extinct relatives. In just a decade, they have found countless sites where these hominins lived, stretching hundreds of thousands of years into the past. Arabia, it seems, wasn’t a mere stopover for hominins as they moved out of Africa into the wider world. It was somewhere they settled for long stretches of time. Indeed, many researchers now think Arabia should be thought of as part of a “greater Africa”, and that the peninsula played an important role in human evolution and expansion across the world.
For decades, Africa has been seen as the cradle of humanity. The oldest known hominins arose there around 7 million years ago and stayed on the continent for a long time, evolving into various forms including those that gave us famous fossils such as Ardi and Lucy. While some groups started to wander further afield from about 2 million years ago, Africa remained central to our story. The earliest known remains of our species, , also known as modern humans, are from Africa. There we emerged around 300,000 years ago, and there we pretty much remained until around 60,000 years ago, when a single out-of-Africa migration carried modern humans all around the world – or so anthropologists thought.
“Until recently, almost nothing was known about hominins in Arabia”
“We had a very straightforward scenario,” says at the Max Planck Institute for the Science of Human History in Jena, Germany. On this reading, Arabia was a mere pit stop for modern humans as they power-walked into Europe, Asia and elsewhere. “It was just on the route out of Africa,” says Institute for Chemical Ecology, also in Jena, Germany. “Some people even said there was no prehistory in Arabia.”
As a result of these assumptions, until recently was known about hominins in Arabia. Some spectacular rock art sites had been found, but they were 10,000 years old at most (see “Ancient art of Arabia“). Then, a decade ago, a loose coalition of researchers began looking for evidence of earlier occupation, in projects like Petraglia’s and another called . “We sort of all came together at the right time,” says , also at the Max Planck Institute for the Science of Human History.
A crucial driving force was the growing understanding of prehistoric climate change. Over the past few decades, palaeoclimatologists have used records such as deep-sea sediments and ice cores to figure out what the climate was like long ago – and climate modellers have laboured to understand these shifts. These efforts revealed that throughout the past 2.5 million years – the period when there has been permanent ice at both poles – Earth’s average temperature has yo-yoed up and down. Cooler periods called glacials saw ice sheets advance from the poles, while warmer interglacials saw them retreat. in Arabia, as well as the neighbouring Sahara in Africa. , the monsoon rains shifted north so that these areas were to become burning desert again during glacials, when the rain returned south.
To Petraglia and his colleagues, this suggested that Arabia had many rivers and , so they began looking for them. “Lo and behold, the first season we went to some of these places where we thought we had ancient lakes – bam! – we hit them,” he says. The first was 1 in what is now the Nefud desert of Saudi Arabia. In 2011, they described finding the remains of a lake, mostly concealed by wind-blown sand, that measured at least 4 kilometres by 20 kilometres. In the 75,000-year-old sediments they found evidence of grasses and trees – along with stone tools indicating that hominins had lived there.
Since then, Petraglia’s team and others have published many similar findings. “We now know there are about 10,000 palaeolakes of Arabia,” he says. “We’ve only been to a couple of hundred. On 70 per cent of those we found fossils or archaeology.” Hominins even lived in what is now the Rub’ al-Khali desert. At Mundafan Al-Buhayrah, a flat region that was once a lake, the team from between 100,000 and 80,000 years ago.
Occupations tended to : was wet, and either left or died out when it dried. “This cyclicity is key to everything,” says Petraglia. Even the wet periods were no picnic, says Groucutt. “During those periods of much more rainfall, it would have been extremely seasonal.” Nevertheless, conditions were wet enough for hippopotamuses to have inhabited the peninsula. “Hippos need perennial water, metres deep,” says Groucutt.
Another discovery is that the geography of Arabia had powerful effects on the communities living there. Those residing in northern Arabia probably still had contact with populations in Africa and elsewhere, says Groucutt. This is reflected in the similarities between the stone tools they made. In contrast, the inhabitants of southern Arabia tended to develop distinctive tools, suggesting they were isolated.
But who were these people? Despite the abundance of stone tools, hominin bones have been lacking. That’s because the desert isn’t well suited to preserving them, says Scerri. “It’s hyper-arid, you get windstorms, sediments crumble.”
That hasn’t stopped some people from speculating. In 2011, of Tübingen in Germany and his team had claimed that H. sapiens were in the region around that time. The assertion was based on stone tools found at Jebel Faya in what is now the United Arab Emirates, dating from , which look similar to tools made by modern humans living in Africa at the time. But .
Then, in 2018, a team that included Scerri, Groucutt and Petraglia got lucky. At Al Wusta in the Nefud desert in northern Saudi Arabia, in the remains of yet another lake, they found a single finger bone. “The day we found that, none of us could really believe it,” says Scerri. It was fortuitous, says Groucutt, because finger bones vary a lot between hominins. This one bone was enough to identify the species: H. sapiens. And .
First settlers?
That’s a clincher, but there is reason to believe that H. sapiens were in Arabia before then. Just last year, Petraglia and his colleagues claimed that a set of footprints made between 121,000 and 112,000 years ago at Alathar palaeolake in Saudi Arabia , but “we have had no flak on our interpretation”, says Petraglia. In any case, people had time to reach Arabia to make the footprints: the oldest remains of modern humans found so far are from Jebel Irhoud in Morocco, and are between 250,000 and 350,000 years old. Furthermore, modern human remains dating to 210,000 years ago have been found in Greece, and a jawbone found in Israel dates to at least 177,000 years ago.
Although the 85,000-year-old Al Wusta finger bone is still the only known hominin bone found in Arabia, the stone tool record goes back much further. Stone tools found at An Nasim in Saudi Arabia are 300,000 years old. And, in 2018, a team including Petraglia, Scerri and Groucutt described their , also in Saudi Arabia. There, a dried-up lake was once surrounded by fertile grasslands, inhabited by elephants, Asiatic wild asses and water birds. Some of the animal bones seem to have cut marks and other signs of hominin activity – and there were stone tools. The to between 300,000 and 500,000 years ago.
If hominins were living in Arabia 500,000 years ago, they were almost certainly not modern humans. Many other hominins were roaming Eurasia at that time (see “Possible Arabians”), but the prime suspects are the Neanderthals. “I am pretty sure Neanderthals were there, at least in the northern parts of Arabia,” says Scerri. She notes that have been , the region to the north of Arabia that includes modern Israel. “We have stone tools in Arabia that are very similar to [ones found in] sites with Neanderthal fossils,” says Scerri.
Neanderthals and modern humans probably weren’t the only early Arabians. Scerri and many others suspect the region was something of a melting pot, with multiple groups moving in and out as the climate became wetter and drier. “My guess is we’re going to be looking at a whole variety of potentially different hominin species, almost all of whom could probably interbreed,” says of Liverpool, UK, who is a member of the DISPERSE project.
What does all this mean for human evolution? There are two key questions: how did modern humans use Arabia once they began moving outside Africa, and what role did Arabia play in the prior evolution of H. sapiens?
For Petraglia, the discovery of so many hominin sites over such a wide span of time, and with such a close correlation to shifting climate, demolishes the narrative of a single migration by modern humans out of Africa around 60,000 years ago. That idea was already foundering thanks to the growing number of modern human fossils found outside Africa before the supposed migration. But Arabia lends weight to the idea that there were multiple migrations, every time the climate and ecosystems became favourable.
“One model that I’ve been promoting is a multiple dispersals model of Homo sapiens through time,” says Petraglia. “Not just one event, but many events and interbreeding as they went along.” In this model, the reason genetics points to a significant shift 60,000 years ago isn’t a big out-of-Africa migration, but an increase in the overall size of the human population. “In other words, there may be genetic swamping of small populations that were present in Eurasia earlier,” says Petraglia. This would create “the illusion” of a single large dispersal, he says.
Accidental migrants
The discoveries in Arabia also show that modern humans didn’t stick to the coasts when migrating out of Africa, as has sometimes been suggested. There is no doubt that some did travel that way. For example, Sinclair has found evidence of people living in several sites on Arabia’s Red Sea coast, including and . But, one way or another, the lake finds show that they also crossed the centre of the peninsula.
The migrants would have been small groups of hunter-gatherers, not large populations. There is no reason to think they had a goal in mind. “People weren’t aiming for anywhere,” says Groucutt. “They were just roaming around and the opportunities changed a bit, the monsoon moved a bit further north, and over time they, by accident, moved.”
This points to a deeper and larger message about our evolutionary origins. Arabia is technically part of Eurasia because of a divide in the underlying tectonic plates. But as far as African hominins were concerned, it was all one contiguous landmass – and palaeoanthropologists are starting to see it that way too. “I believe Arabia is part of a greater Africa,” says Sinclair.
Scerri goes even further. “Parts of south-west Asia, which are the neighbouring region to Africa, at times probably were part of the core area of human evolution,” she says. She has argued for “African multiregionalism”, a scenario in which Africa was home to multiple H. sapiens populations that were sometimes isolated and sometimes interbred, depending on which regions were liveable. Arabia was one more place early humans could live, making it a part of the melting pot from which humanity emerged.
In other words, we are all ultimately from Africa – it’s just that we need to reconsider our notion of where Africa ends. The Arabian landscapes shaped our species as surely as the savannahs, forests and coasts of Africa. The interior of the Rub’ al-Khali may be a searing desert today, but once upon a time it was home to our distant ancestors.
Ancient art of Arabia
Human ancestors have inhabited the Arabian peninsula for hundreds of thousands of years, at times when the climate was wetter there. Much of the evidence of their presence has eroded away. However, beginning around 10,000 years ago there is a rich record of prehistoric art and artefacts. This tells a story of societies and environments in flux.
Older rock art often shows people hunting wild animals, but later pieces tend to show herding. In many places, older art has been partially overwritten, with artists keeping the human figures but replacing the animals. “There’s clearly a cultural memory, almost a dialogue between these hunting scenes and pastoral scenes,” says Institute for the Science of Human History in Jena, Germany.
Rock art also reveals the changing fauna of the region. Images at Shuwaymis in north-west Saudi Arabia, dating from more than 8000 years ago, suggest that . Here, and at a second Saudi Arabian site called Jubbah, there are paintings of lesser kudu – a type of antelope that today inhabits the forests of east Africa – and possibly aurochs, the wild species from which cattle were domesticated.
At the , artists carved life-size camels and other animals into rock, in most cases more than 8000 years ago. “They look like sculptures coming out of the rock,” says Guagnin. Many people must have been involved in their creation: raw materials for tools had to be brought in from 30 kilometres away, and the sculptures are so high that scaffolding may have been needed. “We think there was a lot of communal effort,” she says.
The same is true for mustatils, huge stone monuments in which low walls surround a central courtyard. More than 1000 of these have been found in the north-west of Saudi Arabia, and some are over 7000 years old, making them older than Stonehenge and the pyramids of Egypt. Each one clearly . Guagnin suspects that people moved around for most of the year, but at the end of the wet season, food may have been abundant enough for them to gather. “There was feasting or maybe even collecting of trophies, so these were big symbolic events and it was important for people to meet up,” she says.
Possible Arabians
Emerging evidence reveals Arabia to have been inhabited from as early as 500,000 years ago. The list of hominins whose eras fit this time span and who may have lived there is quite long.
Modern humans
Era: 300,000 years ago to present Our species’ core homeland was Africa. The oldest fossil evidence from Arabia is 85,000 years ago, but that is likely to be pushed back as we continue to look for fossils in the region.
Neanderthals
800,000-400,000 years ago to 40,000 years ago Neanderthals are known from Europe and western Asia, sometimes roaming as far east as the Altai mountains in Siberia. They made it to Israel and may well have gone south into Arabia.
Denisovans
800,000-400,000 years ago to to at least 43,000 years ago
Denisovans were a sister group of the Neanderthals, known from a handful of sites in east Asia. Evidence suggests Arabia was too far to the west of their homeland – but that may change.
Homo erectus
The earliest hominin known to have lived outside Africa, H. erectus, reached as far east as Java. It seems likely to have inhabited Arabia at times.
Nesher Ramla Homo
Approximately 420,000 years ago to 140,000 years ago
Only described in 2021, the Nesher Ramla Homo may possibly be an ancestor of Neanderthals. It is known from one site in Israel, but could have ventured south.
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