Nick Longrich

Why did Homo sapiens take over the world while our closest relatives, the Neanderthals, went extinct? It’s entirely possible we were just smarter- and that’s the obvious, intuitive, and widely accepted explanation- but there’s surprisingly little evidence that it’s true. Neanderthals had big brains, comparable to ours. They seem to have had the ability to hear, and presumably to speak language. They made sophisticated tools. They made art and jewellery. They were smart, and it’s possible that the average Neanderthal was about as smart as the average human. This raises a curious possibility. Maybe the crucial differences weren’t at the individual level, but in how we connected to one another, in our societies.

250,000 years ago Europe and western Asia were Neanderthal lands. Homo sapiens meanwhile had a more restricted distribution, inhabiting southern Africa. Then, around 100,000 years ago, modern humans migrated out of Africa, and met the Neanderthals in the Middle East. By around 40,000 years ago, Neanderthals disappeared from Asia and Europe, replaced by humans. The slow, inevitable replacement of Neanderthals by Homo sapiens - as far as we know, the Neanderthals were never able to successfully push back and reclaim territory they lost- suggests modern humans had some advantage. But it doesn’t tell us what it was. Were humans more adept with technology, or language? Or was it something else entirely?

Our ideas about Neanderthals have changed radically in recent years as we’ve learned more about their tools, their lives, and their DNA. Anthropologists once saw Neanderthals as dull-witted brutes. But recent archaeological finds increasingly suggest they rivalled us in intelligence. Neanderthals mastered fire before we did. They made complex tools, like throwing spears with Levallois points, and beautiful hand-axes. Stone tools exhibit a range of complexity, and while the most sophisticated Neanderthal tools are less complex than those made by American Indians or Upper Paleolithic Europeans, they rival the stone tools made by many hunter-gatherer groups like the Bushmen and Australian aborigines until recent times.

Neanderthals were deadly hunters, taking large, dangerous game like mammoths and woolly rhinos, and small but agile animals like rabbits and birds. They gathered plants, seeds and shellfish. Like modern hunter-gatherers like the Bushmen, they were ominivorous and opportunistic. And hunting and foraging all those species demanded deep understanding of nature.

Neanderthal hand-axes, Aisne, France. Metropolitan Museum of art

Neanderthals also had a sense of beauty and artistry, making beads, stringing shells and teeth on strings to make necklaces, and making cave paintings. Even their tools have a sense of artistry- their hand-axes have proportions, shape, and symmetry which seem to go beyond what is necessary for a purely functional tool. Looking at Neanderthal stone tools one can’t help but admire their beauty; it’s likely they did too.

Neanderthals were also spiritual people. They buried their dead with flowers; stone circles found inside caves may be Neanderthal shrines. Their cave art probably had, like the art of modern hunter-gatherers, a spiritual purpose, different in sophistication but not in function from the paintings of Michelangelo that adorn the Sistine Chapel in Rome. Like modern hunter-gatherers, Neanderthal lives were probably steeped in superstition and magic; their skies full of gods, the caves inhabited by ancestor-spirits.

Neanderthal cave art, Spain, 60,000 years ago.

The fact that we took so long to displace them suggests that they must have been very close to us in terms of intelligence. Humans are deadly hunters; everywhere we’ve gone we’ve wiped out the local megafauna- mammoths and mastodons, ground sloths, wooly rhinos. We’re the most deadly creature that’s ever evolved, the cause of a major mass extinction. And yet against the Neanderthals it took millennia to displace them and wipe them out. The Mongol Empire was built in less than a hundred years, Alexander built his empire in 13 years, Cortez conquered the Aztecs in just two years. Depending on when we left Africa, humans may have first encountered the Neanderthals as far back as 125,000 years ago, when advanced stone tools appear in Arabia, and they persisted in Europe until at least 40,000 years, so our battles may have lasted close to 100,000 years. If Neanderthals were grunting idiots as we once thought, why did it take so long to displace them?

Then there’s the fact we sometimes had children together. Many and maybe most of the encounters between our species were hostile, but occasionally we put aside our differences and treated each other with humanity as, well, fellow humans. Neanderthals couldn’t have been that different from us if we met, married, and formed families to raise children.

But despite this, we encountered them many times, over many millennia, and the result was always the same. They disappeared; we remained. We had something they didn’t.

The Social Network

It’s possible that our brains simply worked in a different way than theirs, but its also possible that the key differences weren’t so much at the individual level, as at the societal level, not in the people but something that emerges from the interactions between them.

Consider two large tech companies in competition- say, Microsoft competing with Apple to enter the market for music players and smartphones, and failing to displace the iPod and then the iPhone. Why does Apple just make a better hardware product? Both companies are highly selective and have rigorous hiring processes, and employ extremely clever people. So it’s highly unlikely if we measured the skulls of all the Apple engineers we’d find they had a substantial advantage in cranial capacity over the Microsoft engineers. The difference probably doesn’t lie in the individual engineers. Instead, it’s the way they interact- their culture, their social structures- that determines the outcome. These are things that can’t be easily predicted by taking calipers to the skull of an engineer, because they’re the result of interactions between the engineers- they’re emergent properties of these corporations.

Emergent properties are those that result from interactions between the components- life is an example of an emergent property. We mostly consist of hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur atoms; but it’s the interactions between those atoms, their arrangements, the movements and the dance they make, that makes a human a human, and not a cat or a dog or a bunch of chemicals in a water solution. In the same way humans are more than just atoms, human cultures are more than just individuals.

Humans are a social species, like orcas, elephants, wolves, bees, termites or ants. That means it’s impossible to understand humans in isolation, any more than you can understand a honeybee without considering the colony it lives in. We prize our individuality, but an individual’s survival is tied to larger social groups, like a bee’s fate depends on its colony’s survival. We can survive in isolation, but only with difficulty. Throughout most of history, isolation from the group, social death, quickly led to death.

It is therefore impossible to understand the survival of humans, and the demise of the Neanderthals, by seeing them solely in terms individuals. We can’t just extrapolate from the skull to the Neanderthal and stop there, we have to think in terms of the groups in which they lived.

Modern hunter-gatherers provide our best guess at how early humans and Neanderthals lived. People like the Namibia’s Bushmen and Tanzania’s Hadzabe traditionally gather families to form seminomadic bands of ten to 60 people. These bands set up huts in a home camp, and move every few months depending on food and water availability. The bands then combine into a loosely organised tribe- smaller networks forming part of a larger network- which can consist of a thousand people or more.

These tribes lack hierachical structures- there is no overall chief or Big Man to order people what to do, to force them into battle or tell them how to worship, or seize their possessions, the way a chief or a king might. Instead they’re linked together into this larger group by shared language and religion, marriages, blood relationships and friendships, a common sense of identity, and so the bands in the tribes tend stick together rather than trying to fight one another. This is almost certainly the ancestral human social structure, the way our ancestors lived 300,000 years ago. Neanderthal societies were likely very similar to ours- but with one crucial difference. Their social groups were smaller.

And we know this because Neanderthals had lower genetic diversity.

In small populations, genes are easily lost. If one person in ten carries a gene for curly hair, then in a ten-person band, one death could remove the gene from the population. In a band of fifty, five people would carry the gene - in effect, multiple backup copies. So over time, small groups tend to lose genetic variation, either due to natural selection against those genes, or just bad luck, ending up with a lower diversity of genes. And it’s possible to use this principle to make guesses about population sizes in Neanderthals, by looking at their genetic diversity.

Recently, DNA was sequenced from the bones and teeth of eleven Neanderthals, which were found in a cave in the Altai Mountains of Siberia. Several of these individuals were closely related, including a father-daughter pair— they were from a single band. And they showed low genetic diversity.

Because we inherit two sets of chromosomes- one from our mother, one from our father- we carry two copies of each gene. Often, we have two different versions of a single gene- you might get a gene for blue eyes from your mother, and one for brown eyes from your father. But the Altai Neanderthals often had just one version of each gene. That low diversity allows us to make some guesses about how big their communities were, and models suggest they lived in small bands— probably averaging just 20 people.

It’s possible Neanderthal anatomy favoured small group sizes. Being robust and muscular, Neanderthals were heavier than us. Each Neanderthal needed more food, so the land could support fewer big Neanderthals than small Homo sapiens. And Neanderthals may have mainly eaten eaten meat. Meat-eaters can get fewer calories from a square mile of land than people eating both meat and plants, again leading to lower population densities.

Group size matters

Bigger groups gave us an edge.

One reason is that larger groups provide an advantage in battle. Neanderthals were likely good fighters. They were strong and skilled with throwing spears, and as we’ve seen successfully held off the advance of humans for tens of thousands of years. Humans were smaller and more lightly built, and we may only have been able to counter the Neanderthals and their spears once bows were invented around 70,000 years ago (bows have less stopping power than spears and similar range, but they’re are far more accurate, and therefore more effective at long range). But even assuming the average Neanderthal and human warrior were equally dangerous in battle- or if Neanderthal fighters even had a slight edge- humans would have had a numeric advantage. They could bring more fighters to battle, and even when they lost, they could absorb more losses.

Big societies have other, subtler advantages, however. Larger bands have more brains. More brains to solve problems, remember lore about hunting and gathering plants, and techniques for crafting tools and sewing clothing. Just as big groups have higher genetic diversity, they will have higher memetic diversity, more ideas.

The number of possible links in a network- a telephone network, the internet, or a human society- increases exponentially with the number of nodes, dramatically increasing the capacity for information exchange and the robusticity of the network.

And more people means more connections. Network connections increase exponentially with network size, following Metcalfe’s Law. A 20-person band has 190 possible connections between members, which seems like a lot. But a band of 60 people will have 1770 possible connections.

And information flows through these connections: news about movements of people and animals; ideas for technology; words, songs, customs, myths. A larger group can gather more information, process more information, relay that information more effectively. If a single human is like a sort of biological computer, our societies are like the internet, linking us together to take advantage of flows of information. As the internet grew from two nodes, to four nodes, to billions, it became exponentially more complex— almost like a living thing, it behaves in complex, unpredictable ways. And so too as our social networks grew in size, our cultures became more complex, more intelligent.

Swarm Intelligence

*Leafcutter ants cooperate to gather leaves, which they then feed to a fungus they grow for food.*

Consider ants. An individual ant isn’t smart. But the interactions between millions of ants lets colonies make elaborate nests, forage for food, and hunt and kill animals hundreds or thousands of times an ant’s size. Likewise, humans groups do things no one person can.

The design of a large building or a car is beyond what any single person can do. No single programmer could create a complex piece of computer software like a browser, word processor or a computer game, or organize a military campaign, run a company, run a country, or an economy.

Groups can do incredibly stupid things of course- they’re susceptible to manias and panics, they can come to support destructive leaders, destructive wars, and destructive ideas. Not every emergent behavior that emerges from a group is adaptive. This isn’t true just of humans, it’s true of any social group. Sometimes ants get lost and start literally walking in circles- one ant following the other, following the one in front of it, and so on, back to the first ant- until the ants all die of exhaustion. So we have not just emergent intelligence, but emergent stupidity. Anyone who has ever been in a meeting in academia or business will recognize this phenomenon- you can take a lot of individually clever people and put them together and collectively, we all make a very dumb decision.

Starship re-enters the atmosphere. A complex tasks like the design, manufacture and launch of a spacecraft is far beyond what any single human can accomplish individually- and depends on innovations made by thousands of other people in science, engineering, and business.

But these pathologies notwithstanding, groups are also capable of incredible things, like uncovering how evolution works, or bringing light and electricity and internet to billions of people, or hurling the Voyager II probe out of our gravity well top of a giant rocket, out past Neptune and into the depths of space. The intelligence of an ant swarm is far beyond the intelligence of a single ant, and in the same way a human society has an intelligence, an ability to take in information, learn, adapt, and respond, that far exceeds what any single human can do.

And if the individuals in a group are similar in intelligence, the size of a group is one of the most important qualities in determining its complexity, and just how intelligent it can be. Almost all the groups that run our world- writing software, designing spacecraft, waging war, negotiating for peace- are large groups, consisting of thousands of people.

Humans are extraordinary animals. But our unique strength doesn’t lie simply in having big brains (whales and elephants have these) or in having huge social groups (zebras and wildebeest form huge herds). We’re unique in combining these things in a way no other species does, to create uniquely large, complex societies.

To paraphrase John Dunne, no man, and no Neanderthal, is an island. We’re all part of something larger. And throughout history, humans have formed larger and larger social groups: bands, tribes, cities, nation-states, international alliances, cooperating to solve problems and compete more effectively against other groups.

It may be this unique ability to build extraordinary large, complex networks and communities that gave Homo sapiens the edge, both against nature, and against other hominin species.