Neanderthal DNA reveals split from humans

Strands of DNA recovered from the fossilised leg bone of a Neanderthal have shed light on the fragility of this ancient hominid species and pinpointed when they first split from what were to become modern humans.

The 38 000-year-old bone was unearthed in a cave in Vindija in Croatia and has become part of a landmark project to read the entire genetic sequence of Neanderthals, a feat scientists believe will help reveal how modern humans evolved into the world’s dominant species.

Researchers at the Max-Planck Institute for Evolutionary Anthropology in Leipzig, Germany, read the complete DNA sequence held in tiny biological powerhouses called mitochondria, which provide energy for cells. The mitochondria are only passed down the female line, so can be used to trace the species back to an ancestral ”Eve”, the mother of all Neanderthals.

The team analysed the DNA of 13 genes from the Neanderthal mitochondria and found they were distinctly different to modern humans, suggesting Neanderthals never, or rarely, interbred with early humans. The genetic material shows that a Neanderthal ”Eve” lived around 660 000 years ago, when the species last shared a common ancestor with humans.

Further tests on the DNA revealed surprisingly few evolutionary changes, suggesting that the Neanderthals may only ever have existed in relatively small numbers with less than 10 000 alive at any one time.

”This has implications for our picture of Neanderthals and perhaps the reasons for their extinction. If the population was teetering on the brink for hundreds of thousands of years, it may change our impression of what it would have taken to make them go extinct rather than if there were millions of them,” said Adrian Briggs, a molecular biologist who co-authored a report on the work in the journal Cell.

Theories of what drove the Neanderthals to extinction range from an inability to adapt to a quickly changing environment, to genocide by early humans. The species is thought to have died out in Europe around 30 000 years ago, shortly after the arrival of early humans.

Neanderthals were short and stocky and well adapted to a cold climate. The tallest male, found in a cave in France, was only 1,71m tall.

Despite having barrel chests, strong ridges above their eyes and a lack of chins, their brains were, on average, larger than those of modern humans.

Some fossil evidence suggests that they were occasional cannibals, but more commonly hunted large animals including horses and mammoths.

Neanderthal remains dating back 400 000 years suggest they crafted tools and weapons and buried their dead. The Leipzig team has read 4% of the Neanderthal’s entire genetic code and hopes to complete the full sequence by the end of the year.

Comparing the Neanderthal genome with the human genetic sequence should highlight subtle genetic differences such as genes for improved brain capacity and other traits that underpin what it means to be human. —

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