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
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
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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