人类的进化

　　You look familiar

　　你，似曾相识

　　Another piece of humanity’s family tree is fitted into place

　　确定另一支人类谱系

　　THE opening scene of Mel Brooks’s film “History of the World: Part One” dispenses with human origins in one line: “And the ape stood, and became man.” Would that it were that easy for palaeontologists to sort out. The transition to humanity is generally agreed to have occurred between Australopithecus, a genus of small-brained, bipedal primates whose most famous member is a fossil nicknamed “Lucy”, and the big-brained species Homo erectus. But pinning down when precisely this took place, and which of the various australopithecine species were involved, has been challenging. Now the most human-like australopithecine found to date is clarifying things—and staking a claim to be the species from which early humans evolved.

　　梅尔布鲁克斯的电影“世界历史：第一部”一开场就用一句台词概括了人类的起源：“猿猴站立起来了，然后变成了人”。对古生物学家来说，（人类的起源）要是真能如此解释，那也未免太容易了。人们普遍认为，人类是在南猿（Australopithecus）,（一种脑量小，靠两脚行走的灵长类动物。其最有名的成员是一个外号叫“露西”的化石)和直立猿人（Homo erectus）（一种脑量大的物种）之间完成人类进化过渡的。但至于这段过渡期确切发生在什么时候，又属于众多南猿物种的哪一分支，人们众说纷纭。而目前发现的与人类长得最像的南猿，让一切变得清晰起来，同时，它也被确定是后来进化为早期人类的物种。

　　Fossils of the new species, Australopithecus sediba, were discovered in 2008 in a cave in South Africa. Initial research, led by Lee Berger of the University of the Witwatersrand, in Johannesburg, concluded that the species came too late in the fossil record to be the ancestor of the Homo lineage. This week, however, a range of new research into sediba, again led by Dr Berger, has been published in Science. These studies conclude that sediba did in fact predate Homo erectus and, moreover, that parts of its anatomy are surprisingly similar to modern man.

　　新发现的物种化石---南猿源泉种（Australopithecus sediba）于2008年在南非一个山洞中被发现。约翰内斯堡的威特沃特斯兰德大学教授Lee Berger，带领的研究团队经初步研究发现，新物种是化石史上最接近猿人谱系（Homo lineage）的祖先。本周，科学杂志发表了 Berger博士对源泉种的一系列新发现，称源泉种实际上要早于直立猿人，并且其结构的某些部分与现代人也极为相似。

　　The fossils examined in the Science papers are of an adolescent boy and an adult woman. They are well preserved, and encased in sediments that allow uncommonly precise dating. They lived 1.977m years ago, predating the appearance of Homo erectus by 77,000 years. The period is an especially muddled one for palaeontology, being full of fragmentary fossils that are difficult to assign either to Homo or to Australopithecus. The sediba fossils, by contrast, have some of the most complete features in the early human record.

　　“科学”杂志发表的论文研究的化石对象，一个是少年，一个是成年女子。这两具化石保存完好，由于是在沉积层出土，所以可以很精确的确定它们的年代。他们生活在197,7000年前，比直立猿人早出现7,7000年。这段时期令古生物学家一直很迷惑不解，因为所有的化石碎片很难确定到底是属于南猿还是直立猿人。相比较而言，源泉种化石具有部分早期人类最完整的特征。

　　The new studies centre on the most telling bits of anatomy in the story of human evolution: the brain, pelvis, hands and feet. The brain itself does not fossilise, but the inside of the cranium retains an impression of its contours. The researchers mapped these with high-powered X-ray beams to create a three-dimensional model of the surface of sediba’s brain. They found that its size was on a par with other australopithecines, but its shape was more like that of a human brain. Specifically, the frontal lobes, which are the seat in modern humans of higher cognitive functions such as abstract reasoning, looked more humanlike in sediba’s brain than they do in the brains of other australopithecines. That suggests the neurological changes which gave rise to humanity may have predated the brain’s expansion—an event that had, hitherto, been regarded as crucial to the emergence of humans.

　　最新的研究把重点放在研究人类进化最有说服力的结构部位：脑，骨盆，手和脚。脑部分本身是不会变成化石的，但在头盖骨内部却还保留着脑的轮廓。研究人员借助高功率X射线，描绘出了源泉种脑表面的三维模型。他们发现源泉种的脑尺寸与其它南猿一样，但是其形状则更像人类的大脑。特别是大脑前庭部分，它使现代人具有较高的认知能力—例如抽象推理的能力，而相比较南猿来说，源泉种的大脑前庭更像人类。这表明，人类产生所依赖的大脑神经上的变化，有可能在大脑变大之前就已经出现------这也是迄今为止被认为是人类诞生的关键因素。

　　The hands, feet and pelvis of sediba indicate that it both climbed trees and walked upright, though with a different gait from that of humans or chimpanzees. The species may have been a toolmaker, as its hand allowed for a human-like grip. Sediba’s pelvis, an upright butterfly shape, is likewise reminiscent of the human one. It therefore sheds light on a longstanding debate: whether it was bipedalism or giving birth to babies with large heads that drove changes in the shape of the human pelvis. Adult sediba (and therefore, presumably, their babies) had small heads, which indicates that walking upright was the advantage brought by the modern pelvis. All of which makes sediba more similar to modern humans than are other australopithecines—and more similar, even, than Homo habilis, until now seen as one of the earliest humans. The consensus had been that habilis was a transitional form between Australopithecus and Homo erectus. Dr Berger posits that sediba may have evolved directly into Homo erectus, leaving habilis as an evolutionary sideline, and not even part of the genus Homo. Slowly, then, the origin of the strange assemblage of characters that makes a human being human is emerging. As the oracle said, the beginning of wisdom is: know thyself.

　　从源泉种的手、脚和骨盆来看，源泉种既能爬树又能直立行走，但步态与人类或是猩猩有点不一样。 这种物种有可能也会制作工具，因为它的手可以像人类一样抓取东西。源泉种的骨盆，呈垂直蝴蝶形，同样让人看到人类骨盘的影子。这也使长期的争论变得清晰起来：是否这种物种是用两只脚行走，或是它所生的后代头比较大，使其骨盆发生了改变，和人类的骨盆形状一样。成年的源泉种头比较小，这也表明，南猿在骨盆进化之后，直立行走才变为可能。所有这些使得源泉种比其它南猿，甚至比能人（Homo habilis）更像现代人类，直到现在有人把源泉种视为最早的人类成员之一。普遍认为，能人是介于南猿与直立猿人之间。Berger博士认为，源泉种有可能直接进化为直立猿人，而能人却是进化过程中的一个分支，甚至和源泉种不属于一个类别。之后，一些奇特的人类特征才开始慢慢出现。如（古希腊）神谕所说：智慧从认识自己开始！