双语时事系列57:人类进化新说

2009-10-22 00:00:00来源：网络

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双语时事：原始人化石揭示人类进化新说

After 15 years of rumors, researchers made public fossils from a 4.4 million-year-old human forebear they say reveals that our ancestors were more modern than scholars had assumed, widening the evolutionary gulf separating humankind from apes and chimpanzees.

The highlight of the extensive fossil trove was a female skeleton a million years older than the iconic bones of Lucy, the primitive female figure that has long symbolized humankind's beginnings.

An international research team led by paleoanthropologist Tim White at the University of California, Berkeley, unveiled on Thursday remains from 36 males, females and young of an ancient prehuman species called Ardipithecus ramidus, unearthed in the Awash region of Ethiopia starting in 1994. The creatures take their scientific name from the word for 'root' in the local Afar language. They aren't the oldest known fossils of hominids -- as prehuman species and their relatives are called -- but constitute the most complete set discovered so far.

'It is not a chimp, and it is not human,' said Dr. White. 'It gives us a new perspective on our origins. We opened a time capsule from a time and place that we knew nothing about.'

Although the differences between humans, apes and chimps today are legion, we all shared a common ancestor six million years or so ago. These fossils suggest that the common ancestor -- still undiscovered -- resembled a chimp much less than researchers have always believed.

In fact, so many traits in modern chimps and apes are missing from these early hominids that researchers now question the notion that chimps and apes are a repository of primitive traits once shared by our ancestors. 'We all thought the ancestral animal would look more like a chimp,' said Yale University anthropologist Andrew Hill.

Instead, the new finds show that what seems most ancient about modern chimps and apes -- such as canine fangs, long limbs with hooked fingers for swinging through trees, and hands designed for knuckle-walking -- may actually be more recent developments, the researchers said. In that sense, the human hand today actually may be the more primitive appendage, they said.

'It is the chimps and gorillas that have been evolving like crazy in terms of limbs and locomotion, not hominids,' said Kent State University anthropologist Owen Lovejoy, a senior scientist on the research team. 'We took a different tack. We went social.'

Documented in 11 research papers to be published Friday in Science, the fossils offer a detailed look at a species of sturdy, small-brained creatures that dwelled in an ancient African glade of hackberry, fig and palm trees, by a river that long ago turned to stone. Despite their antiquity, their bodies were already starting to presage humanity, the scientists said.

Unlike modern apes and chimps, these hominids had supple wrists, strong thumbs, flexible fingers and power-grip palms shaped to grasp objects like sticks and stones firmly. They were primed for tool use, even though it would be another two million years or so before our ancestors began to fashion the first stone blades, choppers and axes.

There is no way to gauge these creatures' intelligence, but they had brains barely bigger than a golf-club head -- far smaller than the more recent species, called Australopithecus afarensis, to which the Lucy skeleton belonged.

The creatures were still evolving the ability to walk upright, with a big toe better suited for grasping branches than stepping smartly along, an analysis of their anatomy shows. They made their home in the woods, not on the open savannah grasslands long considered the main arena of human development. Yet their upright posture, distinctive pelvis and other toes suggest they walked easily enough. Most important, they showed no sign they walked on their knuckles, as contemporary chimps and apes do.

'They are not what one would have predicted,' said anthropologist Bernard Wood at George Washington University.

Already, the discoveries have experts reworking the human pedigree. They undoubtedly will shape debates about human origins for years to come, as scholars argue whether these creatures should be counted among our most ancient direct ancestors or cataloged as an intriguing dead-end.

研究人员在闪烁其辞15年后，终于公开了440万年前人类始祖的化石。他们说，这些化石显示我们的祖先比学者们所假定的更现代，从而加大了人类与猿和猩猩之间的进化鸿沟。

一具被称作“阿迪”(Ardi)的古老化石彻底改变了我们对于人类起源的现有认识。“阿迪”比我们过去发现的化石更好地解释了人类起源，并说明人跟黑猩猩并没有我们过去以为的那么亲。发现的大量化石中，最重要的是一具女性骨骼。这具骨骼的年代比“露西”(Lucy)的骨骼早了100万年，后者一直被当作人类起源的象征。

加州大学伯克利分校(University of California, Berkeley)古人类学家怀特(Tim White)领导的一个国际研究小组周四公布了36具遗骨，它们分别属于男人、女人和孩子，来自一个名为“拉密达地猿”(Ardipithecus ramidus)的前人类物种，从1994年起在埃塞俄比亚的Awash地区陆续出土。其科学名称来自当地土语Afar中的“根”这个词。这些化石并不是已知最早的原始人化石，但却是迄今发现的原始人化石中最完整的。

怀特说，他们不是黑猩猩，但也不是人类。这些化石给了我们一个有关人类起源的新视角。我们打开了一个时空舱，它来自我们一无所知的时空。

虽然人、猿、猩猩现在有诸多差异，但大约600万年前我们都拥有共同的祖先。这些化石表明，目前仍然不为人知的这个共同祖先与黑猩猩的相似程度远远低于研究人员一直以来的看法。

事实上，现代的猩猩和猿身上的诸多特点在这些早期原始人身上都不具备，以至研究人员现在开始质疑我们的祖先曾经一度具有猩猩和猿的一些原始特点这一看法。耶鲁大学的人类学家希尔(Andrew Hill)说，我们本来都觉得老祖宗看上去会更像猩猩。

研究人员说，相反，新的发现表明，现代猩猩和猿看起来最古老的特点（比如犬齿，长长的四肢，便于其在树木间荡悠的可弯曲手指，以及适合于用指关节拄地行走的上肢）实际上可能是后来才演化出来的。这样的话，人类如今的手实际上可能是更古老的零件。

肯特大学人类学家、该研究小组的资深科学家洛夫乔伊(Owen Lovejoy)说，黑猩猩和大猩猩在四肢和移动能力方面疯狂进化，原始人并没有这样。我们选择了不同的进化方向，转向社会化。

上周五发表在《科学》(Science)杂志上的11篇研究论文记载了这些化石，它们可以让人详细了解一个强健的、脑容量很小的物种，其生活在古代非洲的一片夹杂着朴树、无花果和棕榈树的林地，旁边有条河，河流现在早已变成岩石。科学家们说，虽然很古老，但这一前人类物种的身体已经开始显示出人类的特点。

与现代猿猴和猩猩不同，这些原始人有着柔软的腕关节、强壮的拇指、灵活的手指和握力很强的手掌，可以牢牢地抓握棍子和石头等物品。他们已经会使用工具，虽然我们的祖先还要再过大约200万年才开始制作最早的石刀、石斧等等。

这些生物的智力无从测量，但他们的大脑比高尔夫球棍前端大不了多少──远远小于更接近人类的南方古猿阿法种(Australopithecus afarensis)，“露西”就属于这一人种。

从解剖学角度进行的分析显示，这一物种的直立行走能力仍在进化之中，它们的大脚趾更适合抓握树枝，而不是灵巧地向前走。他们在林间安家，而不是在开阔的草原，人们一直认为草原才是人类进化过程中的主要活动场所。不过它们直立的身体姿态、特殊的骨盆和其他脚趾表明它们行走已经很轻松了。最重要的是，它们没有显示出依靠前肢支撑行走的迹象，现代的猩猩和猿行走时依然需要用前肢辅助。

乔治华盛顿大学(George Washington University)的人类学家伍德(Bernard Wood)说，它们跟我们预想的不一样。

这些发现已经在令专家们重新修订人类谱系。它们无疑会在未来的许多年里引发有关人类起源的争论，对于这些生物应当算作人类最古老的直系祖先还是应当归入进化历程中一个令人迷惑的死胡同，学者们会争论不休。

本文选自上海新东方学校惠瑾的博客，博客链接地址：http://blog.hjenglish.com/huijin