Ian Sample “Ancient human bone helps date our first sex with Neanderthals” http://www.theguardian.com/science/2014/oct/22/ancient-human-bone-sex-neanderthals-oldest-genome-dna
独逸のMax Planck Institute for Evolutionary AnthropologyのSvante Pääbo氏*2とJanet Kelso氏*3が率いる研究ティームは、2008年に西シベリアUst’-Ishim*4のirtysh川畔*5で偶然に発見された４万5000年前のホモ・サピエンスの大腿骨から、ホモ・サピエンスとネアンデルタール人との混血が５〜６万年前に行われたことを推定した。
Qiaomei Fu, Heng Li, Priya Moorjani,Flora Jay,Sergey M. Slepchenko,Aleksei A. Bondarev, Philip L. F. Johnson, Ayinuer Aximu-Petri, Kay Prüfer, Cesare de Filippo, Matthias Meyer, Nicolas Zwyns, Domingo C. Salazar-García, Yaroslav V. Kuzmin, Susan G. Keates, Pavel A. Kosintsev, Dmitry I. Razhev, Michael P. Richards, Nikolai V. Peristov, Michael Lachmann, Katerina Douka, Thomas F. G. Higham, Montgomery Slatkin, Jean-Jacques Hublin, David Reich et al. “Genome sequence of a 45,000-year-old modern human from western Siberia” Nature 514, 23 October 2014, pp.445–449 http://www.nature.com/nature/journal/v514/n7523/full/nature13810.html
We present the high-quality genome sequence of a ~45,000-year-old modern human male from Siberia. This individual derives from a population that lived before―or simultaneously with―the separation of the populations in western and eastern Eurasia and carries a similar amount of Neanderthal ancestry as present-day Eurasians. However, the genomic segments of Neanderthal ancestry are substantially longer than those observed in present-day individuals, indicating that Neanderthal gene flow into the ancestors of this individual occurred 7,000–13,000 years before he lived. We estimate an autosomal mutation rate of 0.4 × 10−9 to 0.6 × 10−9 per site per year, a Y chromosomal mutation rate of 0.7 × 10−9 to 0.9 × 10−9 per site per year based on the additional substitutions that have occurred in present-day non-Africans compared to this genome, and a mitochondrial mutation rate of 1.8 × 10−8 to 3.2 × 10−8 per site per year based on the age of the bone.
Radiocarbon dating of pieces of the leg bone put the remains at around 45,000 years old. The team went on to extract DNA from the bone, which allowed them to reconstruct the oldest modern human genome ever.
The genetic material showed that the thigh bone belonged to a man who carried about 2% Neanderthal DNA, a similar amount to people from Europe and Asia today. The presence of Neanderthal DNA meant that interbreeding between them and modern humans must have taken place at least 45,000 years ago.
But amid the DNA were more clues to when humans and Neanderthals reproduced. Strands of Neanderthal DNA found in modern humans can act like a biological clock, because they are fragmented more and more with each generation since interbreeding happened. The strands of Neanderthal DNA in the Siberian man were on average three times longer than those seen in people alive today. Working backwards, the scientists calculate that Neanderthals contributed to the man’s genetic ancestry somewhere between 7,000 and 13,000 years before he lived.
The findings, published in the journal Nature, suggest that humans and Neanderthals had reproductive sex around 50,000 to 60,000 years ago, though other couplings might well have happened later. Until now, estimates for interbreeding have varied enormously, ranging from 37,000 to 86,000 years ago.
“What we think may be the case is that the ancestors of the Ust’-Ishim man met and interbred with Neanderthals during the initial early admixture event that is shared by all non-Africans at between 50,000 and 60,000 years ago, and perhaps somewhere in the middle East,” Kelso told the Guardian.
But a small number of fragments of Neanderthal DNA in the man’s genome were longer than expected given how many generations had passed. Those might be evidence of his ancestors breeding with Neanderthals closer to the time he was born.
“Everyone outside Africa has about same amount of Neanderthal DNA. It seems to be something early on where one really mixed with Neanderthals in a serious way,” said Pääbo. “Since that happened I wouldn’t be surprised if, now and again, one did it here and there later on too.”
Nicky Phillips “Scientists sequence genome of 45,000-year-old man” http://www.smh.com.au/technology/sci-tech/scientists-sequence-genome-of-45000yearold-man-20141022-119yvy.html
Prior to the latest study, the oldest modern human genome came from the 24,000-year-old remains of a boy buried at Mal’ta near Lake Baikal in easterbn Siberia.
Maanasa Raghavan, Pontus Skoglund, Kelly E. Graf, Mait Metspalu, Anders Albrechtsen, Ida Moltke, Simon Rasmussen,Thomas W. Stafford Jr, Ludovic Orlando, Ene Metspalu, Monika Karmin, Kristiina Tambets, Siiri Rootsi, Reedik Mägi, Paula F. Campos, Elena Balanovska, Oleg Balanovsky, Elza Khusnutdinova, Sergey Litvinov, Ludmila P. Osipova, Sardana A. Fedorova, Mikhail I. Voevoda, Michael DeGiorgio, Thomas Sicheritz-Ponten, Søren Brunak et al. “Upper Palaeolithic Siberian genome reveals dual ancestry of Native Americans” Nature 505(02 January 2014),87–91 http://www.nature.com/nature/journal/v505/n7481/full/nature12736.html
*2:See http://www.eva.mpg.de/genetics/staff/paabo/home.html 但し、Natureに掲載された論文の著者としてはリスト・アップされていない。
*7:Ian Sample “New species of human ancestor found in Siberia” http://www.guardian.co.uk/science/2010/mar/24/new-human-species-siberia Mentioned in http://d.hatena.ne.jp/sumita-m/20100325/1269494305