Extinction of the Neanderthals: Why Did They Disappear?

The extinction of the Neanderthals is one of the great puzzles of human prehistory. These close relatives of modern humans lived across Europe and western Asia for several hundred thousand years, then disappeared as a distinct population around 40,000 years ago, shortly after Homo sapiens spread into their range. Scientists still debate why, and the answer probably involves several causes acting together.

Who the Neanderthals were

Neanderthals (Homo neanderthalensis) were a human population that evolved in western Eurasia. Fossils with early Neanderthal features appear by about 400,000 years ago, and classic Neanderthals are well known from about 130,000 years ago onwards. Their range stretched from Britain and Iberia in the west to the Altai Mountains of Siberia in the east, and south into the Levant.

They were strong, stocky people adapted to cold climates, with large brains. They made sophisticated stone tools of the Mousterian tradition, controlled fire, hunted large animals, used pigments and in some cases buried their dead. Their way of life was successful enough to survive several glacial cycles.

When they disappeared

Pinning down the date of extinction has been difficult. Radiocarbon dating works only back to about 50,000 years, and at the limit of the method tiny amounts of modern contamination can make samples look much younger than they really are.

In 2014 a team led by Tom Higham at the University of Oxford published new radiocarbon dates from about 40 sites from Spain to Russia, using improved methods to remove contamination. They concluded that Neanderthals disappeared from Europe between about 41,000 and 39,000 years ago. They also found that extinction was patchy: Neanderthals vanished from different regions at different times, and they overlapped with modern humans in Europe for roughly 2,600 to 5,400 years.

Some researchers have argued for later survival in the far south of Europe. Clive Finlayson and colleagues proposed in 2006 that Neanderthals lived in Gorham’s Cave in Gibraltar until about 28,000 years ago or even later. Others have argued for late survival in parts of Iberia south of the Ebro River. These later dates remain controversial, and many specialists think they may reflect contamination or mixed layers.

The arrival of modern humans

The disappearance of the Neanderthals followed the spread of Homo sapiens out of Africa and into Europe. Modern humans were present at Bacho Kiro Cave in Bulgaria by about 45,000 years ago, and a tooth from Grotte Mandrin in southern France suggests a brief presence there around 54,000 years ago, although that interpretation is debated.

Because Neanderthals disappeared soon after modern humans arrived in each region, many researchers see a link. The question is what the link was.

Leading explanations

Competition

The most widely discussed idea is that modern humans out-competed Neanderthals for food and territory. Modern humans may have had larger social networks, more efficient hunting technologies, better clothing or wider exchange of materials over long distances. Even a small advantage, repeated over many generations, could push a smaller population into decline. There is little direct evidence of violence between the two groups, so competition is usually imagined as indirect rather than as warfare.

Climate

The period between about 60,000 and 30,000 years ago saw rapid swings of climate, including sudden cold phases known as Heinrich events. A large volcanic eruption in the Campanian region of Italy around 39,000 to 40,000 years ago spread ash across south-eastern Europe. Some researchers argue that such changes fragmented Neanderthal habitats. However, Neanderthals had survived earlier climate swings, so climate alone seems unlikely to explain their extinction.

Small populations and disease

Ancient DNA shows that Neanderthals had low genetic diversity, consistent with small, scattered populations. Some genomes, such as one from the Altai Mountains, show signs of inbreeding. Small populations are vulnerable to chance events, accidents and the loss of skills. Some scientists have suggested that diseases carried by incoming modern humans may also have played a role, though this is hard to test.

Absorption through interbreeding

Neanderthals and modern humans interbred. Most people with ancestry from outside Africa carry roughly 1 to 2 per cent Neanderthal DNA. A modern human jawbone from Peștera cu Oase in Romania, dated to about 42,000 to 37,000 years ago, belonged to someone with a Neanderthal ancestor only four to six generations back. Some researchers therefore argue that Neanderthals were partly absorbed into the larger modern human population rather than simply dying out. Read more on Neanderthal interbreeding.

Evidence from the archaeological record

Stone tools offer another window on the period. In France and northern Spain, a tool industry called the Châtelperronian appears in the last millennia of Neanderthal life. It combines older Mousterian techniques with blades and personal ornaments such as pierced teeth, features usually linked with modern humans. At the Grotte du Renne at Arcy-sur-Cure, these objects were found with Neanderthal remains.

Some researchers see the Châtelperronian as evidence that late Neanderthals developed new behaviours on their own; others suggest they copied or traded with incoming modern humans, or that layers were mixed during excavation. In Italy and Greece a comparable industry, the Uluzzian, was once credited to Neanderthals but is now more often attributed to modern humans. Either way, the period of overlap was one of contact and change rather than a single sudden replacement.

Population estimates also matter. Calculations based on site numbers and genetic diversity suggest that Neanderthals may have numbered only in the tens of thousands across their whole range at any one time, and possibly fewer. Modern human groups arriving from the east may have been larger and better connected, so that a gradual demographic imbalance could, over a few thousand years, leave Neanderthals with too few partners and too few neighbours to sustain themselves.

Myths and facts

A common myth is that Neanderthals were wiped out in a single violent conquest. The evidence instead points to a long, uneven process lasting several thousand years and varying from region to region. Another misconception is that Neanderthals died out because they could not speak or think symbolically. Neanderthals shared the FOXP2 gene variant associated with speech in modern humans, and their use of pigments and ornaments suggests symbolic behaviour, although how complex their language was cannot be known.

A combination of causes

Most specialists now favour a combination of factors. Neanderthal populations were probably already small and fragmented, perhaps partly because of climate instability. The arrival of modern humans added competition for the same resources, while interbreeding drew some Neanderthal ancestry into the newcomers’ gene pool. Over a few thousand years, the distinct Neanderthal population disappeared.

Earlier explanations that portrayed Neanderthals as mentally inferior have lost favour. Evidence of Neanderthal pigments, ornaments, complex tools and burial practices, such as at La Chapelle-aux-Saints, suggests they were capable people whose disappearance owed more to numbers and circumstances than to any lack of intelligence.

By the numbers

Timeline

• c. 400,000 years ago: Early Neanderthal features appear in European fossils.
• c. 54,000 years ago: Possible brief presence of modern humans at Grotte Mandrin, France (debated).
• c. 45,000 years ago: Modern humans are present at Bacho Kiro Cave, Bulgaria.
• c. 42,000–37,000 years ago: The Oase 1 individual in Romania has a recent Neanderthal ancestor.
• c. 41,000–39,000 years ago: Neanderthals disappear from most of Europe.
• c. 40,000–39,000 years ago: The Campanian Ignimbrite eruption in Italy.
• 2010: The first draft Neanderthal genome reveals interbreeding with modern humans.
• 2014: Higham and colleagues publish a Europe-wide chronology of Neanderthal disappearance.

Why it matters

The extinction of the Neanderthals marks the point at which Homo sapiens became the only human species in Europe, and eventually in the world. Understanding why it happened sheds light on how human populations compete, adapt and mix, and it reminds us that the Neanderthals are not wholly gone: part of their legacy lives on in the DNA of billions of people.