Why Homo sapiens, not Neanderthals, took over the world

Why did humans come to dominate the world while the Neanderthals, our nearest relatives, died out? Perhaps we were simply more intelligent, yet the evidence for that idea is remarkably limited.

Neanderthals possessed large brains, language and advanced tools. They created art and jewellery. Their intelligence raises an intriguing possibility: perhaps the decisive distinction lay not with individuals, but with the societies they formed.

Around 250,000 years ago, Neanderthals occupied Europe and western Asia, while Homo sapiens lived in southern Africa. Although estimates differ, modern humans may have left Africa about 100,000 years ago.

By 40,000 years ago, Neanderthals had vanished from Asia and Europe, with humans taking their place. Their gradual, apparently inevitable displacement indicates that humans held some advantage, although its nature remains unclear.

Anthropologists once portrayed Neanderthals as unintelligent brutes. More recent archaeological discoveries, however, suggest that their intelligence matched our own.

They controlled fire before humans did. Neanderthals were formidable hunters, killing large prey such as mammoths and woolly rhinoceroses, as well as smaller creatures including rabbits and birds.

They also collected plants, seeds and shellfish. Hunting and foraging across such a range of species required a detailed knowledge of the natural world.

Neanderthals displayed an appreciation of beauty too, producing beads and cave art. They also appear to have been spiritual, burying their dead alongside flowers.

Stone circles discovered within caves may have served as Neanderthal shrines. Like present-day hunter-gatherers, they probably lived in a world rich in superstition and magic, with gods in the sky and ancestor spirits inhabiting caves.

There is also the fact that Homo sapiens and Neanderthals had children together. We were not so different. Yet humans encountered Neanderthals repeatedly over many thousands of years, and the outcome was always the same: they vanished, while we endured.

Hunter-gatherer society

The important differences may therefore have been societal rather than individual. Humans cannot be understood in isolation any more than a honeybee can be understood without its colony. We value individuality, but our survival depends on wider social groups, just as a bee’s fate rests on the survival of its colony.

Modern hunter-gatherers offer the closest indication of how early humans and Neanderthals may have lived. Groups such as Namibia’s Khoisan and Tanzania’s Hadzabe organise families into mobile bands of 10 to 60 people. These bands come together as a loosely structured tribe numbering 1,000 people or more.

Such tribes have no hierarchical organisation, but common language and religion, marriages, kinship ties and friendships connect them. Neanderthal societies may have worked in much the same way, apart from one vital difference: their social groups were smaller.

Tight-knit Neanderthal tribes

Evidence for this comes from the lower genetic diversity found in Neanderthals.

Genes can be readily lost in small populations. If one person in 10 has a gene for curly hair, a single death in a band of 10 could eliminate that gene from the group. In a band of 50, by contrast, five people would have it, creating several back-up copies. Over time, smaller groups therefore tend to lose genetic variation and retain fewer genes.

In 2022, researchers recovered DNA from the bones and teeth of 11 Neanderthals found in a cave in Siberia’s Altai Mountains. Several were relatives, including a father and daughter, and they belonged to one band. They also had low genetic diversity.

We inherit two sets of chromosomes, one from each parent, and consequently have two copies of every gene. Frequently, these are different versions of the same gene: you may inherit a gene for blue eyes from your mother and one for brown eyes from your father.

The Altai Neanderthals, however, often had only one version of each gene. As the study reports, this low diversity indicates that they lived in small bands, probably with an average of only 20 people.

Neanderthal anatomy may itself have encouraged smaller groups. Their sturdy, muscular bodies made them heavier than us, so each individual needed more food. The same area of land could therefore support fewer Neanderthals than Homo sapiens.

They may also have eaten mostly meat. People reliant on meat would obtain fewer calories from the land than those consuming both meat and plants, again resulting in smaller populations.

Why group size matters

If humans lived in larger groups than Neanderthals, that may have given us important advantages.

Strong and adept with spears, Neanderthals were probably effective fighters. More lightly built humans may have compensated by using bows to strike from a distance.

Even if humans and Neanderthals were equally dangerous in combat, a numerical advantage would have allowed humans to field more fighters and withstand greater losses.

Larger societies also bring less obvious benefits. Bigger bands contain more minds: more people to tackle problems, retain knowledge about animals and plants, and preserve methods for making tools and sewing clothes. Just as large groups have greater genetic diversity, they also have a wider diversity of ideas.

More people also create more links. Connections within a network rise exponentially with its size, in line with Metcalfe’s Law. A band of 20 people has 190 possible connections between its members, whereas 60 people have 1770 possible connections.

These links allow information to circulate, including news about people and animal movements, techniques for producing tools, and words, songs and myths. The behaviour of the group also becomes progressively more complex.

Take ants as an example. An individual ant is not intelligent, but the interactions of millions enable colonies to build complex nests, gather food and kill animals many times larger than an ant. In the same way, human groups can achieve what no single person can: designing buildings and cars, writing sophisticated computer programmes, fighting wars, and operating companies and countries.

Humans are not alone in possessing large brains - whales and elephants do too - nor are we alone in forming vast social groups, as zebras and wildebeest make huge herds. What is unique is our combination of both.

To borrow from poet John Dunne, no man - and no Neanderthal - is an island. We are all part of something bigger. Across history, humans have created ever larger social groups: bands, tribes, cities, nation states and international alliances.

It may be, then, that the capacity to construct large social structures gave Homo sapiens an advantage over nature and other hominin species.

Nicholas R. Longrich, Senior Lecturer in Paleontology and Evolutionary Biology, Life Sciences at the University of Bath, University of Bath

This article is republished from The Conversation under a Creative Commons license. Read the original article.