Neanderthal wipeout: was love or war to blame?

Neanderthals are our nearest extinct human relatives. When our ancestors first left Africa for Eurasia about 60,000 years ago, they encountered another human species, the Neanderthals, already walking the Eurasian land mass. Scientific study of Neanderthal fossils reveals fascinating details. They mysteriously died out about 30,000 years ago. I am indebted to Prof David Sheehan, head of UCC's school of biochemistry and cell biology, for acquainting me with an important Irish contribution to the study of Neanderthals.

In 1856 labourers working in the Neander valley, Germany, unearthed bones they thought were the remains of a bear. Subsequent study revealed that the bones belonged to a previously unknown species of early human. In 1859 Charles Darwin published The Origin of Species, proposing that species evolve over time and that Earth is much older than a few thousand years. This set the scene for an important contribution by William King, professor of geology at Queen's College Galway (now NUIG). He observed that the sediments where the Neander fossils lay were at least 30,000 years old and he proposed in 1864 that the remains belong to an extinct human species he named Homo neanderthalensis.

Fossil and genetic evidence indicate that Homo neanderthalensis and modern humans (Homo sapiens) both evolved from a common ancestor 500,000- 200,000 years ago. Both are separate branches (species) of the human family tree. Neanderthals and modern humans lived in the same geographical areas for 30,000-50,000 years and Neanderthals may have interbred with non-African modern humans.

In 2010 scientists compared a draft of the Neanderthal genome with that of modern humans and concluded that most humans have 1-4 per cent Neanderthal DNA. This could be explained either by interbreeding between Neanderthals and modern humans or because the two species share a common ancestor.

Homo neanderthalensis lived during the last Ice Age and their bodies were adapted by natural selection to accommodate these harsh conditions. Neanderthal bodies were shorter and stockier than ours. Their skulls had a sloping forehead, distinct brow ridges, a large middle face, angled cheekbones and a huge nose adapted to humidify and warm the incoming cold, dry air. Neanderthal brains were at least as large as ours.

Neanderthals ate plants but also considerable amounts of meat, because availability of plants dropped significantly during the extreme winters. They were specialised seasonal game hunters using sharp wooden spears, and their fossil bones show a high frequency of fractures similar to professional rodeo riders who regularly tangle with dangerous animals.

Powerful brutes?

Neanderthals were long considered to be powerful, brutish people, able hunters but too primitive to show modern human behaviour. However, findings since the 1950s have challenged this view. In 1957 the remains of eight adults and two infants were discovered in northern Iraq and appear to have been purposefully buried, perhaps accompanied with flowers. Also, examination of the adult skeletons indicated that injuries had been tended and healed, suggesting Neanderthals cared for their sick and wounded.

There is also evidence that Neanderthals used a diverse range of stone tools, used fire, made and wore clothes, made music and appreciated the medicinal qualities of some plants.

Why did Neanderthals suddenly die out? Neanderthals and modern humans may have had little direct contact over tens of thousands of years until, during a particularly cold period, modern humans spread widely across Europe. This may have prevented Neanderthals from returning to areas they once favoured, putting them on a steep, slippery slope towards extinction. Neanderthal numbers declined to the point of extinction over a few thousand years after modern humans moved into Eurasia, and all traces had vanished by about 40,000 years ago.

Some propose that modern humans killed off the Neanderthals. This doesn't seem that likely to me, because it is clear that Neanderthals were formidable hunters and would not be so easily wiped out in battles. The "make love not war" theory proposes that they were assimilated into the much larger modern human stock by interbreeding. Other theories as to why Neanderthals suddenly disappeared invoke climate change or dietary deficiencies, but nobody knows for sure.

[ http://understandingscience.ucc.ie ]