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The Common Ancestor of TB Bacteria and When It First Appeared

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发表于 8-21-2014 18:39:47 | 显示全部楼层 |阅读模式
Nicole Skinner, Seals brought TB to Americas; Bacteria found in ancient Peru remains points to relatively recent origin of the disease and to its spread by sea. Nature, 512: _ (online publication Aug 20, 2014).
www.nature.com/news/seals-brought-tb-to-americas-1.15748

Note:
(a) “In a study published today in Nature, a team led by palaeogeneticist Johannes Krause at the University of Tübingen in Germany provides DNA evidence for this theory [that tuberculosis was present on the continent --the Americas--before European contact]. The researchers present three 1,000-year-old M. tuberculosis genomes extracted from human skeletons found in Peru.”
(i) The German surname Krause: “from Middle High German kruse ‘pitcher,’ ‘jug’” (occupation to make these)
(ii) University of Tübingen
en.wikipedia.org/wiki/University_of_T%C3%BCbingen

(b) The introduction quotes Dr Krause as saying, “Pathogens don’t leave fossils, but they do leave their DNA in the skeleton, teeth and bones of the victims of the disease.”

The first sentence means that bacteria will not become fossilized.

(c) The takeaway is: Until now, "[t]he general opinion in recent years has been that TB emerged about 70,000 years ago, and that modern humans first acquired it before leaving Africa [around 60,000 years ago] * * * [this report concludes TB emerged and] evolved less than 6,000 years ago”

Both are based on calculation of “molecular clock” which theorizes DNA mutates at a constant rate, and that numbers of mutation tells how many years have passed to accumulate those mutations.
(d) The above commentary (for laypersons) introduces a scientific report in the same issue:

Bos KI et al, Pre-Columbian mycobacterial genomes reveal seals as a source of New World human tuberculosis. Nature, 512: _ (online publication Aug 20, 2014).
www.nature.com/nature/journal/vaop/ncurrent/full/nature13591.html
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 楼主| 发表于 8-21-2014 18:40:08 | 显示全部楼层
Archaeologists disagree.

Carl Zimmer‎, Tuberculosis Is Newer Than Thought, Study Says; Tracing a disease’s oriin back less than 6,000 years ago. New York Times, Aug 21, 2014.

Quote:

(a) “Some scientists have argued that tuberculosis spread from  cows to humans when the animals were first domesticated 10,000 years ago. Others have argued that the disease is far older, having evolved about 70,000 years ago, and spread from humans to cows and other animals.

(b) “Before this new study [published yesterday on Nature], the oldest tuberculosis genome [retrieved from humans] was reconstructed from a woman who died in Hungary in 1797.

(c) “The Peruvian [TB]  genomes held two surprises.

“The scientists expected that the [Peruvian] tuberculosis DNA would be closely related to some particular strain of the disease. Instead, they found that it was mostly closely related to animal strains [particularly those found only in seals]. The second surprise came [from the 6,000-year estimation]

(d) Helen Donoghue, an expert on ancient DNA at the University College London “pointed to fossil evidence suggesting tuberculosis is far older than 6,000 years. In Israel, for example, archaeologists have found 9,000-year-old human remains that contain molecules produced by the [TB] bacteria. In a Wyoming cave, they have found 17,000-year-old bison bones with similar markers.

My comment: There is no need to read the rest of the NY Times report.
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