Human evolution: the more we know…
The oldest hominin DNA has been deciphered
The oldest hominin DNA decoded to date was obtained from the thigh of an individual who lived there 300-400 thousand years ago. The almost complete mitochondrial genome is three to four times older than a small section of 100 thousand-year-old Neanderthal DNA, which has been a record holder until now.
Matthias Meyer from the Institute of Evolutionary Anthropology of the Society. Max Planck (Germany) and his colleagues have achieved tremendous success. The bone cleft has already earned a reputation as the most important source of information about human evolution. Now it is also a storehouse of genetic information.
The position of the inhabitants of the Bone Cleft on the evolutionary tree of Homo was in question.
(National Geographic image.)
Over time, DNA breaks down into fragments that become smaller and smaller. Over the past year, Mr. Meyer's group has been developing a method for effectively restoring these pieces. "In such fossils, you will not find truly ancient DNA longer than 35-45 base pairs," the scientist says. "And until recently, DNA of this size was not taken into account."
This year, experts proved the suitability of their method by deciphering the complete mitochondrial genome of a cave bear, which was also isolated from the remains of a Bone Cleft. Then it was the turn of two grams of material obtained from the bone of a hominin.
The biggest problem, of course, was the contamination of the sample. There was so little authentic DNA left in the bone that the DNA of the scientists who conducted the excavations and the analysis itself, despite all precautions, was often found. To get rid of them, experts were looking for sequences in which cytosine residues turned into uracil: this type of damage is characteristic of ancient DNA. Eventually, scientists isolated enough truly ancient sequences to restore an individual's mitochondrial genome by 98%.
Skeletons of at least 28 individuals who lived in the Middle Pleistocene were found in the Cleft of the bones. Traditionally, they are attributed to the Heidelberg man and the very early ancestors of the Neanderthals. However, the analysis of the mitochondrial genome showed that they are closer to the Denisovans – a mysterious group of hominins related to Neanderthals, which is known only by the finger and molar. Their remains were found in Siberia – 7,500 km east of the Sierra de Atapuerca. "The results are unexpected, it is difficult to interpret them," Mr. Meyer admits.
A variant of the pedigree proposed by the authors of the work.
It is unlikely that the inhabitants of the Bone Cleft were Denisovans or their immediate predecessors: the shape of the teeth is completely different. Most likely, either they or their relatives gave birth to both Denisovans and Neanderthals. Or there was some other group of archaic hominins (perhaps an upright man figured in this role), whose mtDNA was inherited by both Denisovans and residents of the Bone Cleft. And then the recent discovery of traces of an unknown ancient hominin in the Denisov genome acquires a new meaning. (Neanderthals and homo sapiens could also inherit these sites, and then lose them: most mtDNA lines die out, even if this biological species continues to exist.)
"Many believed that Denisovans lived only in the east of Eurasia," comments paleoanthropologist John Hawkes from the University of Wisconsin–Madison (USA). – Mitochondrial DNA from the Bone Cleft suggests that the Denisovans were partly descendants of an earlier Western population. They can be the result of mixing a wide variety of population groups."
"Obviously, Neanderthals and Denisovans have very complex roots," sums up Mr. Meyer.
"We are just beginning to understand the relationships of species that have existed for the last 600 thousand years," Chris Stringer of the London Museum of Natural History echoes him. Who knows how many more of them there were – populations unknown to us that recklessly interbred...
Some commentators are disappointed. "The authors have not come to any conclusion," grumbles Emiliano Bruner of the Spanish National Center for the Study of Human Evolution. – Not a step forward, all hypotheses remained in their places." And Mr. Stringer believes that this is normal for a first look at new material.
The only way to resolve the issues is to analyze as much ancient DNA as possible, including the nuclear genome of the inhabitants of the "Cleft of Bones". Obtaining mtDNA has turned out to be very difficult, and isolating nuclear DNA is even more difficult, but Mr. Meyer still hopes to get a few fragments.
National Geographic image.
Today, the oldest genome is approximately 700 thousand years old: this is the genome of a horse whose remains are well preserved in the Siberian permafrost. Until now, it was believed that DNA several hundred thousand years old could be obtained only from samples that fell into such ideal conditions. Mr. Meyer's success significantly expands this range, which is especially pleasing to paleoanthropologists, because the remains of hominins are extremely rare to find in permafrost: our ancestors preferred warmer places.
At the same time, it should be noted that a bone cleft is far from the worst place to store genetic material. It lies at a depth of 30 m underground and half a kilometer from the current entrance to the cave system. The air circulation there is minimal, the temperature is constantly kept at 5-10 ° C. "If permafrost is a great freezer, then a cave is a great refrigerator," Mr. Meyer emphasizes. It is unlikely that such conditions in the Cleft of bones are unique. Nearby there are caves with the remains, presumably, of an upright man and a human predecessor...
The inhabitant of the "Cleft of Bones". He was considered a Heidelberg man and the ancestor of the Neanderthals.
Who he is now is unclear. (Image by Javier Trueba / Madrid Scientific Films.)
The results of the study are published in the journal Nature (Meyer et al., A mitochondrial genome sequence of a hominin from Sima de los Huesos).
Prepared based on the materials of The Scientist, ScienceNOW and other sources.
Portal "Eternal youth" http://vechnayamolodost.ru06.12.2013