万物简史 第644期:永不安分的类人猿(13)（在线收听）

With the fossil record so unhelpful, scientists have turned increasingly to genetic studies, in particular the part known as mitochondrial DNA. Mitochondrial DNA was only discovered in 1964, but by the 1980s some ingenious souls at the University of California at Berkeley had realized that it has two features that lend it a particular convenience as a kind of molecular clock: it is passed on only through the female line, so it doesn't become scrambled with paternal DNA with each new generation, and it mutates about twenty times faster than normal nuclear DNA, making it easier to detect and follow genetic patterns over time. By tracking the rates of mutation they could work out the genetic history and relationships of whole groups of people.

由于化石记录提供的帮助不大，科学家们越来越转向基因研究，特别是那个被称为线粒体DNA的部分。线粒体DNA发现于1964年，但到了20世纪80年代，加利福尼亚大学伯克利分校的一些科学家发现线粒体DNA具备两大特点，可被方便地充当分子钟的角色：首先它只在母系一条线上遗传，因此它不会依附在新的一代的父系DNA螺旋上。其次，它比普通DNA核酸的突变率快20倍，届时使得它的基因模式更容易被测定和跟踪。通过对突变事的跟踪，可以知道人的基因史以及各过基因组之间的相互关系。

In 1987, the Berkeley team, led by the late Allan Wilson, did an analysis of mitochondrial DNA from 147 individuals and declared that the rise of anatomically modern humans occurred in Africa within the last 140,000 years and that "all present-day humans are descended from that population." It was a serious blow to the multiregionalists. But then people began to look a little more closely at the data. One of the most extraordinary points— almost too extraordinary to credit really—was that the "Africans" used in the study were actually African-Americans, whose genes had obviously been subjected to considerable mediation in the past few hundred years. Doubts also soon emerged about the assumed rates of mutations.

1987年，由艾伦·成尔逊领导的伯克利分校的科学家小组通过对147个人的线粒体DNA的研究，最终得出结论，从解剖学的角度来看，现代人类在过去的14万年里出现于非洲，”当今所有的人都是那群人的后代”。对于“多地区起源”论者来说，这是个沉重的打击。但是，接下来人们又对研究所得的数据作了进一步的审察。令人们最感惊讶的是——惊讶得几乎令人难以置信，通常研究中所谓的“非洲人”实际上是非洲——美洲人，他们的基因在过去几百年中显然在很大程度上已经融合。而且，对假定的突变率也很快产生了怀疑。