Tue, Apr 10, 2018 - Page 9 News List

Neanderthals were perhaps capable of many modern human behaviors

Genome sequencing has changed everything we thought about our origins and how we relate to early human species

By Robin McKie  /  The Observer

Ancient DNA studies are overturning our oversimplified vision of our past and are the outcome of a late 20th-century revolution in molecular biology that gave scientists the power to study DNA, the material from which our genes are made, with startling precision.

For the first time, the exact structure and makeup of a gene could be determined and the detailed origins of many inherited illnesses and cancers outlined, setting in motion the slow, ongoing task of developing new treatments.

By contrast, the study of ancient DNA, which uses the same basic technology, began late, but has since flowered far more dramatically.

“It is in the area of shedding light on human migrations — rather than in explaining human biology — that the genome revolution has been a runaway success,” Reich said.

The field’s hesitant start is understandable. In samples from living animals, DNA exists in long, healthy, easily analyzed strands. However, DNA starts to decay the moment an organism dies and those strands quickly fragment, and the longer the passage of time, the shorter the fragments become.

This disintegration poses problems. If, for example, you want to study Neanderthals, who dominated Europe for about 400,000 years and who were close in evolutionary terms to Homo sapiens, DNA from their fossils is going to be in minuscule pieces. The last member of this doomed species died more than 40,000 years ago, after all. Genetic material taken from Neanderthal fossils is also likely to be contaminated with large amounts of DNA from bacteria and vegetation — and sometimes from researchers.

Trying to create a genome from these sullied scraps has been likened, by writer Elizabeth Kolbert, to reassembling “a Manhattan telephone book from pages that have been put through a shredder, mixed with yesterday’s trash and left to rot in a landfill.”

Nevertheless, scientists have persevered and in 2007, geneticist Svante Paabo, of the Max Planck Institute for Evolutionary Anthropology, decided to assemble a team of experts to sequence a Neanderthal genome that would be billions of DNA units in length.

Reich, an innovator in the field of studying population mixtures, was asked to join and has since played a key role in the fledgling field’s remarkable development.

Clean rooms were built, advanced gene sequencers purchased and DNA extracted from Neanderthal bones that had been found in Vindija cave in Croatia. A Neanderthal genome was slowly spliced together from pieces of DNA only a few dozen units in length. It was a brilliant achievement, although Reich makes clear progress was halting.

“The Neanderthal sequences we were working with had a mistake approximately every 200 DNA letters,” he said in his book.

These errors were not due to differences between humans and Neanderthals, but to errors made in analyzing DNA.

It was Reich’s task to get around these problems and help create a meaningful genome of a Neanderthal. From that, scientists could assess just how closely we were related to these ancient people.

His tests succeeded and subsequently showed, to everyone’s surprise, that many modern humans carry small amounts of Neanderthal DNA in their genomes.

“Non-African genomes today are around 1.5 to 2.1 percent Neanderthal in origin,” he said.

So yes, Homo sapiens and Neanderthals had a common ancestor, about 500,000 years ago, before the former evolved as a separate species — in Africa — and the latter as a different species in Europe. Then about 70,000 years ago, when modern humans emerged from Africa, we encountered the Neanderthals, most probably in the Middle East. We briefly mixed and interbred with them before we continued our slow diaspora across the planet.

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