Around 300,000 years ago, when anatomically modern humans first appeared, a half-dozen closely related populations were also running around Africa, Europe, Asia, and the Arabian Peninsula.
Pockets of Homo sapiens intermingled (and even procreated) with communities of Neanderthals, Denisovans, and as-yet unknown others. In southeastern Africa, the diminutive Homo naledi showed signs of cultural learning. On the islands of Indonesia, the long-legged Homo erectus crossed paths with the small-bodied Homo floresiensis (also known as “Hobbits”). The Earth was filled with an array of groups reminiscent of Tolkien’s Middle Earth—different body shapes, different cultures, different tools.
And somehow, in the time since, every single human lineage but ours has gone extinct. In practically the blink of an eye, geologically speaking, a multitude of interacting communities shrank down to only Homo sapiens, creating one of the most fascinating and enduring mysteries in human evolution.
“It’s something that I think paleoanthropologists have not come up with a good explanation for,” says John Hawks, paleoanthropologist at the University of Wisconsin-Madison. “If we look at chimpanzees today, they have something like three or four times the genetic diversity of living people. Gorillas are the same story.”
Humans, meanwhile, have a population of over 8 billion, but the genes of someone living in Australia vs. someone from Liberia are more similar than two populations of chimpanzees separated by no more than a river.
We can only speculate as to how the world might look if our ancestor’s rich diversity were present today.
But by digging into history, we see a world that’s both familiar and strange: a fluctuating climate, megafauna roaming the earth, and many kinds of communities—sometimes thriving, sometimes clinging to survival, but all of them fully alive and interacting.
Welcome to the Pleistocene.
Hippos in London
You could walk for days, weeks, months, and the corridor of green and water and game animals would never end, even as the creatures galloped away, even as other dangerous predators hunted them—and sometimes you. Maybe your kin travel to a different place every season, following the ebb and flow of water and nutrients, and each time you return, it feels like home. But maybe, over time, you’ve traveled so far that the only familiarity to be found is in the daily rhythms of life: gathering food and preparing it, playing games, raising children alongside your friends and family.
When Michael Petraglia thinks of ancient people moving “out of Africa,” he likes to remind himself that humans, in one sense, are just another kind of animal. The director of the Australian Research Centre for Human Evolution at Griffith University, Petraglia, turns to hippos as the example of other creatures spreading across vast distances. At one point, there was an abundance of hippos not just in Africa, but across the Arabian Peninsula, and even up into London.
“Forget about sapiens, if hippos are doing it, you don’t need any special technologies, you don’t need any social network. You just need to be reproductively viable, and you need to have potable water. That’s it,” Petraglia says.
The first world travelers
Much of Petraglia’s research focuses on the ways that climate and environment affected the migration patterns of ancient hominins. At different points in time, the Sahara Desert was a green corridor, stretching across the northern part of Africa and into the Levant and Arabia. Small bands of hunter-gatherers—be they Homo sapiens, Neanderthals, Homo erectus, or Denisovans, could have easily followed the resources they needed and moved across continents over the course of generations.
Sometimes this meant they would become geographically isolated when water dried up and resources disappeared.
Small groups would die out or abandon habitats that had been stable for decades. This hopscotching across terrain allowed our ancestors and sibling lineages to traverse incredible distances on foot.
Consider the tens of thousands of lithic artifacts (stone tools and the materials for producing them) found at Jebel Faya in the Arabian Peninsula, suggesting a population of hominins was there around 125,000 years ago. Or the rock shelter in Krapina, northern Croatia, where, 130,000 years ago, a group of Neanderthal adults and children lived. Others made it all the way to Siberia.
We’ve found Homo erectus fossils on Java, Indonesia, that date between 117,000 and 108,000 years, a distance of more than 10,000 miles away from the species’ origins in Kenya (which would require walking across the United States about five times). The diminutive Hobbits of Flores, who were only about three-and-a-half feet tall and hunted pygmy elephants, were also in Indonesia during the same time period, though we don’t yet know where their ancestors came from.
(And in case you were wondering, the ancient hippo species Hippopotamus antiquus lived across Western and Central Europe and into Asia during this time period; there are modern hippos living in Indonesia today.)
But if traveling vast distances doesn’t differentiate these hominins from hippos, then cultural practices surely do. It’s an important reminder: while we can’t place our perspectives directly onto the past, these were also complex groups of people, with beliefs, desires, and goals outside of securing food and shelter.
Artists and dancers
One of the most unique examples are Homo naledi, who exhibited a strange mixture of primitive and modern features found in a South African cave system. More than 1,000 fossils from at least 15 individuals were discovered in a large cave system in 2013. Because of the fossils’ location in a difficult-to-access part of the cave, some researchers argued that this showed evidence of deliberate burial. They also proposed the hominins used tools to mark walls, and possibly even controlled fire, all the way back to 300,000 years ago. But these remain controversial conclusions, with some archaeologists arguing strongly in favor of cultural practices and others arguing just as strongly against them.
A different type of behavior is evident from 87 Neanderthal footprints along the southwest coast of the Iberian Peninsula, dating back to 106,000 years ago. The fossilized prints showed a range of foot sizes, with the majority likely made by children and adolescents. And while the pattern of the footprints could indicate some kind of hunting strategy, the researchers also hypothesized that some of the tracks could have been left by a child “jumping irregularly as though dancing.” In other words, they might have been engaged in play.
When Penny Spikins thinks about past humans, she tries to keep this social-emotional component in mind. “There would have been children and [the community’s] priority will not just have been providing enough food, but creating an environment of social safety so that everyone collaborates and so that children grow up with a chance to play and feel supported,” Spikins says. “Because those are basic human needs.”
The strangers next door
A professor of archaeology at the University of York, Spikins has looked extensively at the role of emotions in social behavior. She’s particularly fascinated by the differences and similarities between Homo sapiens and Neanderthals. We have multiple pieces of evidence for caregiving among Neanderthals, whether that was assisting a community member in recovering from injuries or raising a child born with severe disabilities. And at the same time, there is also a lot of evidence that many Neanderthal groups were quite isolated and that they engaged in significant inbreeding.
For Spikins, that suggests a different kind of sociality than what may have appeared in anatomically modern humans. “Some of the genetics that we see in our own species, compared to Neanderthals, match some of the genetic changes that we see occurring as wolves become dogs. Neither of those is better,” Spikins says.
But the difference means that Neanderthals may have been less receptive to strangers and novelty. If true, that could have limited their participation in trade networks and cultural innovations.
Yet openness can come with a cost, too—and not just the “oops, that stranger turned out to be hostile” cost. Spikins wrote a paper called “The Geography of Trust and Betrayal,” in which she explored the ways that broken trust could have caused groups to travel great distances in order to avoid seeing one another again.
Imagine you have a trade agreement with a group that provides you with the best rocks for making certain tools. But then they stop providing those materials, because they claim you haven’t fulfilled your side of the bargain. Maybe the disagreement grows so acrimonious that neither group ever wants to see the other again; so your group sets off for the distant horizon, looking for a new place to call home (and better neighbors).
“We forget this in our modern world because we’re kind of stuck where we are,” Spikins says. “But if you’re a mobile group, there’s a lot of moving around.
And the more emotional commitments there are, the more they’re breaking apart. And when they do, because of the level of investment, there’s more of a push. I mean, to get to Australia across 60 kilometers of sea crossing, there’s got to be some kind of push there.”
Though the past had its challenges, it would be misleading to essentialize it as “red in tooth and claw.”
Being Human
What made our ancestors and sibling lineages “human”? Partly the fact of our biology: our brains and bodies adapted to being continent-hopping social mammals, dependent on one another for survival and joy and sex and nurture. And when we saw others who looked both similar and different, sometimes the reaction was fear or violence. But on other occasions—many other occasions—we saw something we recognized. Something familiar enough to bring us together as mates and caretakers.
In the late 1970s, anthropologists discovered two hominin skull fossils in Apidima Cave on the coast of southern Greece. It took decades for researchers to piece together the distorted fossils and realize that one belonged to a Neanderthal some 170,000 years ago, while the other may have been an ancient Homo sapiens from over 200,000 years ago. Although it’s impossible to say for certain whether members of the two species encountered each other in this location, “It’s hard to imagine that somebody who looks like a modern human is going to get [to Greece] without meeting somebody that looks like a Neanderthal,” Hawks says.
An even more stunning example of interactions between species comes from a series of discoveries across Russia and East Asia. Researchers working in the Altai Mountains of Siberia discovered a tiny fossil bone in 2008, from which DNA was extracted. The mitochondrial and nuclear genomes showed it to be a new species, dubbed the “Denisovans.” As more archaeologists have dug deeper into the sediments, they’ve uncovered more bones and stone tools, suggesting occupation of the cave extended from 300,000 years ago to 20,000 years ago. At various points in time, Denisovans, Neanderthals, and Homo sapiens lived there – sometimes at the same time (including a girl whose mother was Neanderthal and father was Denisovan).
Since then, more fossils have been found in the Tibetan Plateau and other parts of China, belonging to the Denisovan lineage (or, as it has more recently been called, Homo longi, “dragon man”). And while it’s rare to find sites with indisputable evidence that multiple species were living and working together simultaneously, the genetic evidence is visible in modern humans.
A surprising family tree
Today, people living in the islands of the southwestern Pacific Ocean have 4 to 6 percent of their DNA from Denisovans. Tibetans who live in a high-altitude, lower-oxygen environment seem to have received the genetic changes that allow for hypoxia tolerance from Denisovans. And we’ve known for years that it’s possible for modern non-African humans to have up to 4 percent of their DNA coming from Neanderthals.
In other words, these people weren’t just our ancient contemporaries—they were our ancestors. Their legacy continues in us today.
Part of what makes the Pleistocene such a fascinating (and aggravating) era to study is the tantalizing pieces of evidence scattered amidst huge gaps. There remain fundamental questions about how Homo sapiens expanded from the continent of Africa to every other part of the world. We don’t know for sure what people ate every day, how they thought, how they interacted with each other.
And because there are only glimmers of light in a deep darkness, the study of humanity’s origins has been deeply shaped by our modern biases.
An incomplete picture
Petraglia points to the fact that he was actively discouraged from doing fieldwork in the Arabian Peninsula because people believed nothing was there—or, if they did find something, that it would be too eroded to be meaningful. Instead, many of his colleagues focused on the Mediterranean, because work had been ongoing there for a century.
“If there’s bias in where we’re working, we’re not going to be able to prove all these things about dispersals or refugia,” Petraglia says. “When I said that Arabia is the missing link, it’s because every time we go out there, we have a new discovery. And when we find something, it modifies our views about all sorts of things.”
The sentiment was echoed by Hawks, who points out that even though Africa is the birthplace of humanity, it has been largely overlooked.
“We have maybe 20 sites [on the continent] across the period of 700,000 years ago to 150,000 years ago where we have some fossil representation that we can say something about,” Hawks says. “We need more exploration in Africa in general, but there are huge patches of African landscape where we have almost no information—West Africa, the Sahel across the Sahara border, the area of southwestern Africa, Angola, and the DRC.”
Hawks hopes that large-scale sediment sampling combined with machine learning might unlock genetic material or proteins that can shed light on the past, even without finding large fossils. But it’s work that will take time and collaboration, and funding.
Of the sites in Africa that have been well-studied, Petraglia points to a cave in coastal Kenya called Panga Ya Saidi as one of his favorites. With the oldest fossils dating to around 80,000 years ago, the cave system was continuously inhabited for many millennia.
“It’s stunning,” Petraglia says. “It’s a cave system in a tropical forest, and some of the roof has collapsed, so you get tropical forest inside the cave. Then you go stand on top of the cave and look at this beautiful coastline, and it’s just so picturesque. It’s idyllic.”
It’s impossible to paint a complete picture of what life was like for humans—Homo sapiens or otherwise—during the Pleistocene. Some surely struggled for survival, hungry, hot, cold, or thirsty. But many others likely lived stable, satisfying lives in their communities, in beautiful locales, perhaps even meeting kindred species. We only have snippets of evidence from their lives hundreds of thousands of years ago. But their legacy lives on in humans today, no matter how different the world may look now.
Lorraine Boissoneault is a Chicago-based writer covering science and history. She is the author of the narrative nonfiction book “The Last Voyageurs.”
