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南非出土灵长类化石-Fossil could rewrite human evolution

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发表于 2010-4-5 21:30 | 显示全部楼层 |阅读模式
While there have been thousands of fossilised fragments from human ancestors unearthed around the world, the story of mankind's progression from simple primates to modern, intelligent humans is far from complete.

The fossil record, which spans millions of years, contains large gaps while in some cases entire species have been described from just a few small pieces of bone.


Some religiously-inspired opponents of evolution theory use the patchy fossil record to argue that humans did not evolve from primates.

But rare fossil finds like the new skeleton from the Malapa caves in Sterkfontein, South Africa, give anthropologists the opportunity to gain huge insights into how our prehistoric ancestors lived and looked.

Africa is now widely accepted as the birthplace of mankind as simple primates evolved into the common ancestor we share with the great apes such as Chimpanzees and Gorillas.

Around 3.9 million years ago a species known as Australopithecus afarenus emerged, which was apelike but also shared certain characteristics with modern humans like the ability to walk upright on two legs.

This bipedalism, however, has remained one of the most contentious issues in human evolution and the evidence for exactly when human ancestors moved onto two feet to walk around remains a hotly debated subject.

The first truly human-like species is thought to have first appeared around 2.5 million years ago in southern and eastern Africa.

Homo habilis, as it has been named, had a 50% larger brain capacity than its predecessors and was the earliest species to be placed by scientists in the genus Homo due to its human-like characteristics.

This larger brain is believed to have given the species an edge that its more apelike ancestors had not benefited from, allowing it to begin to form more complex social groups and to master the use of stone tools.

Despite this growing intelligence, however, Homo habilis is not thought to have shared the sophisticated hunting abilities of its descendants, Homo erectus and later Homo sapiens, that would come to dominate the planet.

There is some evidence they were in fact a staple in the diet of large predators such as Dinofelis, a large scimitar-toothed predatory cat.

But the description of Homo habilis is based on just a few key fossils. The first, which was used to define the species, consisted of a lower jaw found in Tanzania along two fragments of skull and 21 finger, hand and wrist bones.

Another fossil, found in 1973 in Koobi Forea, Kenya, is the most complete Homo habilis cranium found so far. No examples of a pelvis or complete limbs have been discovered.

With so few fossils, scientists have struggled to draw a definitive timeline of how human species evolved and arguments about how individual fossils should be ranked are common.

Experts will be keen to pour over the new fossilised hominid after it is unveiled this week in a bid to unravel more about what its place should be. The team who discovered it will certainly face counter claims about where exactly in the evolutionary tree it should sit.

With an almost-complete skeleton, however, it will be possible to determine whether this early ancestor of humans climbed trees or lived on open grassland and if it stood upright or used its arms to assist when walking.

Armed with this kind of detail, scientists should be able to make far more conclusive statements about how our own species evolved.
 楼主| 发表于 2010-4-5 21:44 | 显示全部楼层
新化石

英国《每日电讯报》4月3日报道,南非金山大学教授李·贝格尔1日在南非斯泰克方丹化石遗址地区考察洞穴系统时发现这一套幼年高级灵长类动物骨架化石。

南非斯泰克方丹化石遗址地区有“人类摇篮”之称。初步研究发现,这套化石属于先前尚未发现的全新物种,这一物种生活在距今大约200万年前。

这套化石埋藏在石灰质洞穴“马拉帕洞”中,出土时趋近完整。科学家认为,包裹这套骨架化石的沉积角砾岩对化石起到良好的保护作用。与这套化石一并出土的还有一些残缺的骨骼残骸化石。

《每日电讯报》报道,这套化石的发现引起不小轰动。南非总统雅各布·祖马已前往金山大学参观这套化石。另外,一部关于这套化石的电视纪录片正在制作之中。

高价值

现阶段,关于这套化石的详细信息尚未对外公开。但一些人类学家猜测,这套骨架化石相当完整,极富研究价值。

1964年命名最早人类“能人”的金山大学教授菲利普·托拜厄斯也受邀参观这套化石。他称这次的发现“令人激动”。“只发现带有几颗牙齿的下颚化石是一回事,”托拜厄斯说,“但同时发现包含下颚、头盖骨、脊柱及四肢等部位的化石就是另外一回事。”

一些科学家认为,如果发现手部骨骼化石就可以研究这一物种的手部灵敏度,进而为确定人类祖先何时能够使用工具提供重要线索。

《每日电讯报》评价这套化石的出土是斯泰克方丹地区1994年以来与人类进化研究相关的最重要发现。1994年,科学家在斯泰克方丹地区发现一套较完整南方古猿骨骼化石。

补空白

一些科学家猜测,与这枚化石相关的研究可能填补人类进化研究中的空白。

按照眼下的理论,大约390万年前,人类祖先南方古猿在非洲出现。经过百万余年的进化,这些灵长类动物逐步学会直立行走,脑容量逐步增大。在大约250万年前,最早的人类“能人”出现。

不过,在南方古猿和“能人”间是否存在过渡物种是科学家尚未解开的难题。一些科学家猜测,1日发现的这套化石可能正属于这个过渡物种。

英国牛津布鲁克斯大学人类进化研究专家西蒙·昂德当博士告诉《每日电讯报》记者:“类似发现有助于我们了解人类祖先究竟在何时真正成为‘人’。”
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