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World’s Oldest DNA¹ Discovered in Million-Year-Old Mammoths

Scientists say they have discovered the oldest DNA on record. It was found in the teeth of mammoths that lived in northeastern Siberia up to 1.2 million years ago.

A mammoth² was a kind of early elephant that lived during the Ice Age. The discovery may lead to a greater understanding of the long-dead species.

DNA is the substance that carries genetic³ information in the cells of living things. The researchers say they recovered and sequenced DNA from the remains⁴ of three mammoths.

The remains -- which were contained in permanently⁵ frozen ground -- were discovered beginning in the 1970s. But scientists at the time did not have the ability to find and remove the DNA.

The oldest of the three mammoths was discovered near the Krestovka River in Siberia. It was about 1.2 million years old. Another, from near the Adycha River, was between 1 to 1.2 million years old. The third, from near the Chukochya River, was around 700,000 years old.

The discovery was by far "the oldest DNA ever recovered," said geneticist Love Dalén of the Center for Palaeogenetics in Sweden. He led the research, which was recently described in a study in the publication Nature.

Until now, the oldest DNA on record was from the leg bone of a horse that lived in Canada's Yukon territory. Scientists estimated the horse was between 560,000 to 780,000 years old.

By comparison, our own species, Homo sapiens, is believed to have first appeared about 300,000 years ago.

The mammoth DNA "was extremely degraded into very small pieces," Dalén said. He explained that scientists had to sequence billions of pieces of genetic material in order to find a final DNA sequence.

Most knowledge about prehistoric⁶ creatures comes from studying skeletal fossils. But ancient DNA can provide much more detailed⁷ information about individual organisms.

However, DNA can be damaged over time. New research methods are now permitting scientists to recover even older DNA.

As these methods further develop, Dalén said he thinks it should be possible to work with DNA that is up to three million years old.

Such methods could lead to a greater knowledge about a number of older species. They can provide valuable information about the way new species formed, which fossils cannot, Dalén said.

However, the methods will not be enough to help us better understand the dinosaurs⁸, which died out about 65 million years ago.

The researchers learned about the development and migration⁹ of mammoths by comparing the DNA to that of mammoths that lived more recently. The last mammoths died out about 4,000 years ago.

DNA from the Krestovka mammoth shows that it split off from the well-known woolly mammoth about 2 million years ago.

Geneticist Tom van der Valk helped lead the research. He said it appears that members of the Krestovka mammoth family were the first mammoths to move from Siberia into North America about 1.5 million years ago.

Words in This Story

species – n. a group of animals or plants that are similar

sequence – v. determine the order of chemical building blocks

degrade – v. damage the quality or condition of something

fossil – n. part of an animal or plant from thousands of year ago, preserved in rock

1 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

2 mammoth   

n.长毛象；adj.长毛象似的，巨大的

参考例句：

• You can only undertake mammoth changes if the finances are there.资金到位的情况下方可进行重大变革。
• Building the new railroad will be a mammoth job.修建那条新铁路将是一项巨大工程。

3 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

4 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

5 permanently   

adv.永恒地，永久地，固定不变地

参考例句：

• The accident left him permanently scarred.那次事故给他留下了永久的伤疤。
• The ship is now permanently moored on the Thames in London.该船现在永久地停泊在伦敦泰晤士河边。

6 prehistoric   

adj.（有记载的）历史以前的，史前的，古老的

参考例句：

• They have found prehistoric remains.他们发现了史前遗迹。
• It was rather like an exhibition of prehistoric electronic equipment.这儿倒像是在展览古老的电子设备。

7 detailed   

adj.详细的，详尽的，极注意细节的，完全的

参考例句：

• He had made a detailed study of the terrain.他对地形作了缜密的研究。
• A detailed list of our publications is available on request.我们的出版物有一份详细的目录备索。

8 dinosaurs   

n.恐龙( dinosaur的名词复数 )；守旧落伍的人，过时落后的东西

参考例句：

• The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
• Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》

9 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。