探索人的本质 The nature of man

Large-scale genetic studies are throwing light on what makes humans human.是什么让人类如此特别——大规模基因研究揭开答案面纱。

HUMANS are peculiar as a species, so what makes them so must be hidden in their genome. To an almost disconcerting extent, though, the human genome looks similar to the genomes of other primates, especially when it comes to the particular proteins it allows cells to make. The powerful new ways of looking at the genome being pioneered by the ENCODE consortium (see article), though, provide ways to seek out the subtle species-specific signals. Lucas Ward and Manolis Kellis of the Massachusetts Institute of Technology report on the results of such sleuthing in a paper just published inScience.
人类，与其他物种迥然不同，人类的基因组中必定隐藏着人类特殊性的线索。可是一直以来我们非常困惑不解，人类和其他灵长类生物的基因组高度类似，特别是编码细胞中某些蛋白的基因。ENCODE（DNA元件百科全书计划的缩写，同时意为“编码”）国际联合计划提供了一个崭新的角度去探索人类基因组的奥秘（见文），帮助我们寻找人类之所以为一个独特物种的潜在线索。美国麻省理工学院的卢卡斯?沃德（Lucas Ward）和马诺里斯?克里斯（Manolis Kellis）共同在《科学》期刊上发表了他们对人类基因组物种特性的研究报告。

The two researchers used data from ENCODE to identify the bits of the genome that actually do things and data from the 1,000 Genomes Project, which has studied human-genome variation across hundreds of people, to discover how much these functional elements vary from person to person. In particular, they looked for telltales that an element is being maintained by natural selection. If something is evolutionarily important then random variations in its DNA sequence will be slowly eliminated from the population, keeping it on the functional straight and narrow in a process known as purifying selection.
这两位科学家首先利用ENCODE的数据定位基因组中的功能元件，之后他们又对照了1000个基因组计划的数据（这些数据记录了几百个人类个体的基因组多样性），比较这些功能元件在人与人之间的差异性。也就是说，他们在寻找功能元件在自然选择过程中是否被保留下来的证据。群体中重要元件的DNA序列中，随机的，变异性高的部分会进化过程中被淘汰，只有具有功能部分会保留下来，在群体中这样的序列会很一致，这一过程称为纯化筛选。

Dr Ward and Dr Kellis found that, in addition to the 5% of human DNA that is conserved between mammals, an additional 4% of human DNA appears to be uniquely human in the sense that it is prone to purifying selection in humans but not in other mammals. Much of this proprietary DNA is involved in regulating gene activity—for example, controlling how much of a protein is produced, rather than changing the nature of the protein itself. This finding is in line with modern thinking that a lot of evolutionary change is connected with regulatory elements rather than actual protein structure. The researchers also found that long non-coding segments that are not conserved in other mammals are in fact highly constrained in humans, suggesting they have human-specific functions.
沃德博士和克里斯博士发现，5%人类DNA在哺乳动物中是保守的（即普遍存在），还有4%的人类DNA是独有的，这些独有的DNA很有可能是人类物种的纯化筛选遗留下的，在其他哺乳动物中被淘汰了。DNA的功能之一是调控基因活性，比如，控制某一个蛋白的合成的数量，但DNA不能改变蛋白本身的性质。这个发现和现在的理论不谋而和：进化改变的主要是调控元件，而非实际的蛋白结构。沃德博士和克里斯博士发现，人类的非编码长片段相当保守，并且是仅仅局限于人类中，而其他哺乳动物中的这类片段变异性高，这一点说明人类的非编码长片段是有功能性的。

Some areas identified as particularly human are the regulation of the cone cells of the retina (which are involved in colour vision) and the regulation of nerve-cell growth. These processes evolved rapidly in man’s primate ancestors but are now under strong purifying selection to maintain their beneficial functions. The implications of that, given humanity’s main distinguishing feature—its huge brain—are obvious. Dr Ward and Dr Kellis have thus created a powerful tool for investigating in detail just what it is that makes a human being human.
他们的研究还阐述了其他一些方面：人类可以调节眼角