Sun, May 12, 2019 - Page 9 News List

‘Spectacular’ jawbone discovery sheds light on ancient Denisovans
下顎化石「讓人驚嘆」 揭開遠古人類謎團

A handout photo released by the Max Planck Institute for Evolutionary Anthropology on May 1 shows a view of the virtual reconstruction of the mandible.
這張馬克斯普朗克演化人類學研究所於五月一日發布的照片,展示電腦虛擬重建後的丹尼索瓦人下顎。

Photo: AFP
照片:法新社

A human jawbone found in a cave on the Tibetan Plateau has revealed new details about the appearance and lifestyle of a mysterious ancient species called Denisovans. The 160,000-year-old fossil, comprising a powerful jaw and unusually large teeth, suggests that these early relatives would have looked something like the most primitive of the Neanderthals. The discovery also shows that Denisovans lived at extremely high altitude and, through interbreeding, may have passed on gene adaptations for this lifestyle to modern-day Sherpas in the region.

Jean-Jacques Hublin, the director of the department of human evolution at the Max Planck Institute for Evolutionary Anthropology in Leipzig and senior author of the find, described this element as “spectacular.” He said: “Until today, nobody imagined that archaic humans could be able to dwell in such an environment.” The dating of the mandible suggests that temperatures on the plateau would have been even harsher than today, when temperatures could plunge to minus-30°C. “It’s a time period colder than now which blows my mind,” said Hublin. “If you find it a challenging environment today, I recommend you try it [then].”

Previously, the only known Denisovan fossils came from a cave in Siberia, and amounted to a finger fragment, some teeth and a few jagged pieces of bone. Crucially, though, scientists were able to extract DNA from inside the ancient bone and by comparing this with other ancient DNA and present-day populations they learned that the species must once have been widespread across Europe and Asia.

The latest fossil represents a crucial link between the Siberian specimens and other Chinese fossils, from which scientists had previously failed to extract DNA, but which show remarkable anatomical similarities to the Tibetan specimen. The fossil was discovered by a monk in Baishiya Karst Cave on the Tibetan Plateau in China’s Gansu province. After finding the jaw in the 1980s, the monk passed it on to a living Buddha, who passed it to one of the scientists behind the latest analysis.

TODAY’S WORDS
今日單字

1. altitude n.

海拔

(hai3 ba2)

2. interbreed v.

跨種繁殖

(kua4 zhong3 fan2 zhi2)

3. adaptation n.

適應

(shi4 ying4)

4. mandible n.

下顎骨

(xia4 e4 gu3)

5. extract v.

萃取

(cui4 qu3)

6. sequence v.

定序

(ding4 xu4)


The scientists were not able to obtain DNA from the sample, but managed to extract proteins from one of the molars. Proteins, like DNA, could be sequenced and the analysis placed the fossil firmly on the Denisovan branch of the evolutionary tree.

The discovery indicates that Denisovans adapted to high-altitude, low-oxygen environments much earlier than the regional arrival of modern humans about 40,000 years ago. It also helps explain how present-day Sherpas and some Tibetan populations came to carry a gene of Denisovan origin — presumably acquired through ancient interbreeding — that allows these populations to cope with hypoxia. “This has been quite puzzling because the [Siberian] cave was not at high altitude,” said Hublin.

Previously scientists had assumed that the gene most probably served a different purpose in Denisovans, such as helping cope with intense physical activity, and that it was later coopted for a different purpose. Prof Chris Stringer, the head of human origins research at the Natural History Museum in London, UK, said: “Now it seems more likely that it originated in high altitude-adapted Denisovans, and could have been passed on directly in the region.” Scientists could not be certain of this, though, because they were unable to extract a genome from the new specimen.

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