经济学人下载:人类进化史-似曾相识

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.

发表在《科学》杂志的该篇论文其研究对象为一个小男孩和一个成年妇女的化石。这些化石保存完好，被封存在可进行精确年代测定的沉积物中，这实属罕见。他们生活于197.7万年前，比直立人早出现7.7万年。该时期属于古生物学上极其混乱的年代，大量化石碎片都很难归类到直立人或南方古猿身上。比较而言，南方古猿sediba化石具备了早期人类一些最完整的特征。

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.

新研究集中于与人类进化史相关的一些最具说服力的特征：如大脑，骨盆，手和脚。大脑本身不会变成化石，但它在颅骨内保留的轮廓特征仍依稀可见。研究人员采用高功率X射线束对其进行映射并绘制出sediba大脑表面的三维模型图。他们发现sediba脑部大小与其它南方古猿并无分别，但形状却更接近人脑。尤其是作为人类抽象推理等高认知功能区域的脑前叶部分，sediba比其它南方古猿更象人类。这表明产生人类的神经系统变化可能早于南方古猿大脑的扩张——大脑扩张至今仍被认为是人类出现的重要因素。