雅思阅读题源New Scientist：Stone tools helpd shape human hands原文
AROUND 1.7 million years ago, our ancestors' tools went from basic rocksbanged together to chipped hand axes. The strength and dexterity needed to make and use the latter quickly shaped ourhands into what they are today – judging by a fossil that belongs to the oldest known anatomically modern hand.
The 1.7-million-year-old Acheulean hand axes were some of the first stone tools. Over the next million years, these chunky teardrop-shaped rocks became widely used before being replaced by finer, more precise flint tips. But how our ancestors' hands evolved into a shape that could make such tools is a bit of a mystery.
Before the hand axes appeared, our ancestors had primitive wrists: good for hanging from branches, but too weak to grasp and handle small objects with much force. And no hand bones had been found to fill the gap between 1.7 million years ago and800,000 years ago – by which time humans had developed the hands we have today. Now, a new fossil is helping bridge that gap.
In 2010, a team led by Fredrick Kyalo Manthi of the National Museums of Kenya discovered an intriguing bone in the north of the country. Carol Ward of the University of Missouri and colleagues identified it as a third metacarpal, the long bone in the palm between the middle finger and the wrist.
Like modern human metacarpals, it has a small lumpat its base – the styloid. This projection helps stabilise the wrist when the hand is gripping small objects between the thumb and fingers. Isotopedating revealed the bone to be about 1.4 million years old. It is likely to have belonged to Homo erectus.
Hand bones of early Homo erectus are almost unknown, says Richard Potts of the Smithsonian Institution in Washington, DC." Having such a
well-preserved specimen begins to answer questions abou thand evolution," he says.
"This is an exciting find," agrees Mary Marzke of Arizona State University in Tempe. It shows that our ancestors' handswere already evolving into their modern form 1.4 million years ago. The forceful, repetitive and sustained processes of tool use, such as digging with rocks, would have made stronger hands desirable, says Marzke.
This would have been particularly useful for knocking off flakes to form and sharpen hand axes, says Potts. Once the important wrist features were in place, it became easier for later hominids to make smaller, finer tools.
Because the fossil is younger than the first tools, Ward's team believe it is the first evidence of anatomy evolving to suit a new technology. As stone tools became more widespread, those who had the wrist structure to use them would have had an evolutionary advantage over their weaker-wristed kin. "The way we look today has been shaped by our be haviour over millions of years," says Ward. She presented the research at this week's meeting of the American Association of Physical Anthropologists in Knoxville, Tennessee.
雅思阅读题源New Scientist：Stone tools helped shape human hands之注释：
1. ancestor 祖先
2. dexterity 灵巧，敏捷。
例句：
Game playing demands strategy, imagination, quick response times and a high level of dexterity.玩游戏要求有策略，有想象力，反应快，动作敏捷。
3. fossil 化石
4. chunky 矮胖，粗短。
例句：
And the firm, synonymous with chunky gold jewellery encrusted with gemstones, expects its performance in 2009 to be even worse than last year.
作为镶嵌着宝石的粗重黄金珠宝代名词的这家公司，预期2009年业绩将比去年还要糟糕。
5. flint 打火石
6. primitive wrist 原始的手腕。
Primary主要的，基本的，基础的，衍生词
primitive是原始的。
7. bridge the gap 填补空白。
8. intriguing 有趣的，迷人的。
例句：
The intriguing book is both thoughtful and informative.这本引人入胜的书既有思想性又富知识性。
9. metacarpal 掌骨
10. Isotopedating 同位素鉴定。Date有鉴定年代的意思。
11. homo erectus 直立人
12. hominid 人种
13. anatomy 解剖学
14. kin 亲戚，同族
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