Monday, March 21, 2016

The Oldest Human Genome Has Been Sequenced & It Could Rewrite Our History

Scientists have discovered remains of the oldest human DNA sequence ever recorded, taken from a cave in Northern Spain known as Sima De Los Huesos, or the pit of bones. This discovery is helping to reconstruct the evolutionary sequence of human species.
The teeth and thigh bones remnants had been fossilized rather than frozen, making DNA extraction comparatively difficult.  Examination of the bones revealed they were 430,000 years old — 100,000 years older than the previous oldest human skull on record, and 200,000 years older than modern humans.
© Kennis & Kennis/Madrid Scientific Films
© Kennis & Kennis/Madrid Scientific Films
To find out more, a team led by Matthias Meyer at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, pieced together parts of the hominin’s nuclear DNA from samples taken from a tooth and a thigh bone, New Scientist reported.
Paleoanthropologist Chris Stringer from the Natural History Museum in London, who wasn’t involved in the research, told Nature Magazine“It’s fascinating and keeps us all on our toes trying to make sense of it all. Instead of just being stuck with trying to resolve the last 100,000 years, we can really start to put some dates from DNA further down the human tree.”

As the fossils were found in Northern Spain, scientists expected the specimen to be Neanderthal. They were accordingly quite surprised to see it more closely related to Denisovans, a sister family to Neanderthals.
Photo Credits: Javier Trueba, Madrid Scientific Films
Photo Credits: Javier Trueba, Madrid Scientific Films
Researchers consulted with LIVESCIENCE, which reported that “this man carried a similar level of Neanderthal ancestry as present-day Eurasians. Their research suggests Neanderthal genes flowed into the ancestors of this man 7,000 to 13,000 years before he lived.”
From this, they concluded that Neanderthals might have mated amongst each other about 50,000 – 60,000 years ago. That gave the sample the genome of Neanderthals. The mitochondria DNA is similar to that of the Denisovans, who apparently lived thousands of kilometers away. The genome of the discovered sample thus resembled more closely that of the Denisovans from Siberia, who were discovered and collated only a few years back, in 2010.
According to Ewen Callaway from Nature Magazine:
The Sima hominin skulls have the beginnings of a prominent brow ridge, as well as other traits typical of Neanderthals. But other features, and uncertainties around their age – some studies put them at 600,000 years old, others closer to 400,000 – convinced many researchers that they might instead belong to an older species known as Homo heidelbergensis.
Previously it had been thought that our ancestors split from the Neanderthal-Denisovan Ancestor between 315,000 and 540,000 years ago. But if matured Neanderthals already existed 430,000 years ago, this split is likely to have taken place much earlier — perhaps as early as 750,000 years ago, as suggested by the collateral researches.
Interesting, that 765,000 date for Denisovan-Neanderthals split could actually point us in the right direction to find our earlier common ancestors. It would seem to discount the theory that the race our evolution is based on, termed homo heidelbergensis, wasn’t actually our linked ancestor, as the species was not thought to have evolved until 50,000 years after the modern species and Neanderthal-Denisovans diverged. This suggests that the likely fugitive to give rise to all three species might have been another species, labelled homo antecessor. This description accords with the remains which were found in Northern Spain, but this time the period is approximately 900,000 years old. The recent discovery has been dubbed one of the greatest fossil discoveries of the past half century and the largest fossil hominin found in Africa, as scientists have recovered the remains of what are thought to be a new species of human relative in South Africa named Homo naledi, adding another piece to the puzzle.
Colin Barras explains at New Scientist:
We know that Denisovans and Neanderthals shared a common ancestor that had split from our modern human lineage. In light of the new nuclear DNA evidence, Meyer’s team suggests this split might have happened as early as 765,000 years ago. Previous DNA studies had dated this split to just 315,000 to 540,000 years ago, says Katerina Harvati-Papatheodorou at the University of Tubingen in Germany.
Studies have shown that even under ideal circumstances, DNA sequencing older than 1.5 million years will be too short to be readable, since they disappear after 65 million years. But nuclear DNA can prolong the deep studies of ancient DNA.
The history of human evolution is complicated, to be sure, and now new further questions are arising which need to be explored. The DNA of the fossils found in the Sima de los Huesos proves that the bones were Neanderthal, but out of those 28 individuals, there was at least one who was related to Denisovans. How this happened is still unknown. There is still much we don’t understand, and much left up to speculation at this point.


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