万物简史 第644期:永不安分的类人猿(13)

With the fossil record so unhelpful, scientists have turned increasingly to genetic¹ studies, in particular the part known as mitochondrial DNA². 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 molecular³ clock: it is passed on only through the female line, so it doesn't become scrambled⁴ with paternal⁵ 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 mutation⁶ 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 descended⁷ 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 genes⁸ had obviously been subjected to considerable mediation⁹ 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。

1 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

2 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

3 molecular   

adj.分子的；克分子的

参考例句：

• The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
• For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时，分子的碰撞就停止了。

4 scrambled   

v.快速爬行( scramble的过去式和过去分词 )；攀登；争夺；（军事飞机）紧急起飞

参考例句：

• Each scrambled for the football at the football ground. 足球场上你争我夺。 来自《现代汉英综合大词典》
• He scrambled awkwardly to his feet. 他笨拙地爬起身来。 来自《简明英汉词典》

5 paternal   

adj.父亲的，像父亲的，父系的，父方的

参考例句：

• I was brought up by my paternal aunt.我是姑姑扶养大的。
• My father wrote me a letter full of his paternal love for me.我父亲给我写了一封充满父爱的信。

6 mutation   

n.变化，变异，转变

参考例句：

• People who have this mutation need less sleep than others.有这种突变的人需要的睡眠比其他人少。
• So far the discussion has centered entirely around mutation in the strict sense.到目前为止，严格来讲，讨论完全集中于围绕突变问题上。

7 descended   

a.为...后裔的，出身于...的

参考例句：

• A mood of melancholy descended on us. 一种悲伤的情绪袭上我们的心头。
• The path descended the hill in a series of zigzags. 小路呈连续的之字形顺着山坡蜿蜒而下。

8 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

9 mediation   

n.调解

参考例句：

• The dispute was settled by mediation of the third country. 这场争端通过第三国的斡旋而得以解决。
• The dispute was settled by mediation. 经调解使争端得以解决。