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2006-01-19

BREAKTHROUGH OF THE YEAR:
Evolution in Action
年度进展：作用中的进化论

Elizabeth Culotta and Elizabeth Pennisi

Equipped with genome data and field observations of organisms from microbes to mammals, biologists made huge strides toward understanding the mechanisms by which living creatures evolve


结合对微生物直到哺乳动物的基因组数据和野外观察，生物学家向着理解生物进化机制前进了一大步

The big breakthrough, of course, was the one Charles Darwin made a century and a half ago. By recognizing how natural selection shapes the diversity of life, he transformed how biologists view the world. But like all pivotal discoveries, Darwin's was a beginning. In the years since the 1859 publication of The Origin of Species, thousands of researchers have sketched life's transitions and explored aspects of evolution Darwin never knew.

最大的进展，当然要属Charles Darwin一个半世纪之间的工作。通过认识到自然选择造就了生命的多样性，他转变了生物学家对世界的认识。但是如同所有关键的发现一样，Darwin的工作只是一个开始。自从1859年《物种起源》发表以来，成千上万的研究者勾画出生命的转变，探索着Darwin所未知的进化。

Today evolution is the foundation of all biology, so basic and all-pervasive that scientists sometimes take its importance for granted. At some level every discovery in biology and medicine rests on it, in much the same way that all terrestrial vertebrates can trace their ancestry back to the first bold fishes to explore land. Each year, researchers worldwide discover enough extraordinary findings tied to evolutionary thinking to fill a book many times as thick as all of Darwin's works put together. This year's volume might start with a proposed rearrangement of the microbes at the base of the tree of life and end with the discovery of 190-million-year-old dinosaur embryos.

今天，进化是所有生物学的基础，如此的基础和普遍，以至于科学家们有时将其重要性视作理所当然。在某种程度上，所有的生物学和医学发现都取决于它，同样，所有的陆上脊椎动物都可以把自己的祖先追溯到那第一条冒冒失失地爬上岸的鱼。每一年，全世界的研究者都有足够特别的，与进化思想有关的发现，这些思想可以组成比所有Darwin的著作厚很多倍的书。今年这卷书的开篇内容是将微生物排在生命树底部的设想，而收尾之作是1亿9千万年前的恐龙胚胎的发现。

Amid this outpouring of results, 2005 stands out as a banner year for uncovering the intricacies of how evolution actually proceeds. Concrete genome data allowed researchers to start pinning down the molecular modifications that drive evolutionary change in organisms from viruses to primates. Painstaking field observations shed new light on how populations diverge to form new species--the mystery of mysteries that baffled Darwin himself. Ironically, also this year some segments of American society fought to dilute the teaching of even the basic facts of evolution. With all this in mind, Science has decided to put Darwin in the spotlight by saluting several dramatic discoveries, each of which reveals the laws of evolution in action.

在这些迸发出的结果之中，2005年是标志性的一年，在这一年人们开始揭示进化如何进行这一错综复杂的问题。具体的基因组数据使得研究人员开始弄明白驱动生物由病毒进化到灵长类动物的分子变化。辛苦的野外观察为研究种群如何分支形成新的物种开拓新的道路——这个问题是困扰Darwin的谜中之谜。具有讽刺意义的是，就在这一年，美国社会的一些组织鼓吹在教学中淡化进化论，甚至是那些进化最基本的事实。为此，Science 决定通过对一些重要的发现表示敬意来将Darwin置于聚光灯下，这些发现揭示了作用中的进化法则。

All in the family
四海一家


One of the most dramatic results came in September, when an international team published the genome of our closest relative, the chimpanzee. With the human genome already in hand, researchers could begin to line up chimp and human DNA and examine, one by one, the 40 million evolutionary events that separate them from us.

最引人注目的结果出现在九月份，一个国际研究团队发表了我们最近的“亲戚”——黑猩猩的基因组。由于已经拥有了人类的基因组，研究者可以将黑猩猩和人类的DNA排列起来，一个个地观察，研究4千万年的进化事件怎样将他们和我们分开。


The genome data confirm our close kinship with chimps: We differ by only about 1% in the nucleotide bases that can be aligned between our two species, and the average protein differs by less than two amino acids. But a surprisingly large chunk of noncoding material is either inserted or deleted in the chimp as compared to the human, bringing the total difference in DNA between our two species to about 4%.

基因组数据证实了我们和黑猩猩之间紧密的“亲戚”关系：我们两个物种之间可配准的核苷酸碱基的差异仅仅为1％，平均每个蛋白相差不到2个氨基酸。但是与人类相比，黑猩猩的基因组中插入或删除了令人惊讶数量的非编码物质，这使得我们两个物种之间的DNA差异达到大约4％。


Somewhere in this catalog of difference lies the genetic blueprint for the traits that make us human: sparse body hair, upright gait, the big and creative brain. We're a long way from pinpointing the genetic underpinnings of such traits, but researchers are already zeroing in on a few genes that may affect brain and behavior. This year, several groups published evidence that natural selection has recently favored a handful of uniquely human genes expressed in the brain, including those for endorphins and a sialic acid receptor, and genes involved in microcephaly.

在这些差异的某些部分含有使我们成为人的那些特征的基因蓝图：稀疏的体毛，直立行走，大而富有创造力的大脑。距离查明这些特征的基因基础，我们还有很长的一段路要走，但是研究者已经瞄准了一些可能影响大脑和行为的基因。今年（2005年），一些研究小组找到了证据证明自然选择在近期赋予了人类一些在大脑表达的、独有的基因，包括表达内啡肽和一种唾液酸受体的基因，以及与头小畸形相关的基因。

The hunt for human genes favored by natural selection will be sped by newly published databases from both private and public teams, which catalog the genetic variability among living people. For example, this year an international team cataloged and arranged more than a million single-nucleotide polymorphisms from four populations into the human haplotype map, or HapMap. These genetic variations are the raw material of evolution and will help reveal recent human evolutionary history.

近来发布的数据库将加快寻找得益于自然选择的人基因的速度，这些数据库既有私人团队建立的，也有公共的，其中包含了现有人群的基因差异。例如，今年一个国际团队收集和整理了四个人种的一百万个以上的寡核苷多态性加入人类单体型图（HapMap）。这些基因变异是进化的原材料，可以帮助揭开近期人类进化的历史。

Probing how species split
探索物种如何分裂

2005 was also a standout year for researchers studying the emergence of new species, or speciation. A new species can form when populations of an existing species begin to adapt in different ways and eventually stop interbreeding. It's easy to see how that can happen when populations wind up on opposite sides of oceans or mountain ranges, for example. But sometimes a single, contiguous population splits into two. Evolutionary theory predicts that this splitting begins when some individuals in a population stop mating with others, but empirical evidence has been scanty. This year field biologists recorded compelling examples of that process, some of which featured surprisingly rapid evolution in organisms' shape and behavior.

2005年也是研究新物种出现，或称物种形成，的科学家们作出杰出工作的一年。一个新物种的形成可以通过其中的一些种群开始适应不同的环境，并逐渐停止杂种繁殖来完成。例如，可以很容易理解当种群向大洋或山脉的反向移动时，新物种就会形成。但是有时候一个单个的、毗邻的种群分裂成两个物种。进化理论预测这种分裂始于这个种群中的一些个体停止与其它个体交配，但是经验性的证据还很少。今年，野外科学家记录了这个过程的一些引人注目的例子，其中一些具有使得生物体形状和活动快速进化的特征。

For example, birds called European blackcaps sharing breeding grounds in southern Germany and Austria are going their own ways--literally and figuratively. Sightings over the decades have shown that ever more of these warblers migrate to northerly grounds in the winter rather than heading south. Isotopic data revealed that northerly migrants reach the common breeding ground earlier and mate with one another before southerly migrants arrive. This difference in timing may one day drive the two populations to become two species.


例如，称作欧洲黑顶莺的鸟在德国和奥地利有繁殖地，它们正在各自走向自己的路——这不仅仅是比喻。几十年的观察显示这些鸟在冬天更多地迁往北方而不是向南飞。同位素数据显示北方的候鸟较早到达共同繁殖地并开始彼此交配，然后南方的候鸟才赶来。这个差异终有一天会导致这两个种群变为两个物种。

Two races of European corn borers sharing the same field may also be splitting up. The caterpillars have come to prefer different plants as they grow--one sticks to corn, and the other eats hops and mugwort--and they emit different pheromones, ensuring that they attract only their own kind.

两种在同一田地里的欧洲玉米螟虫也产生了分裂。在毛虫的生长中它们喜欢不同的植物——一种喜欢玉米，一种喜欢蛇麻草和艾蒿。它们因此释放不同的信息素，使它们只吸引自己的同类。

Biologists have also predicted that these kinds of behavioral traits may keep incipient species separate even when geographically isolated populations somehow wind up back in the same place. Again, examples have been few. But this year, researchers found that simple differences in male wing color, plus rapid changes in the numbers of chromosomes, were enough to maintain separate identities in reunited species of butterflies, and that Hawaiian crickets needed only unique songs to stay separate. In each case, the number of species observed today suggests that these traits have also led to rapid speciation, at a rate previously seen only in African cichlids.

生物学家们还预测，即使地理上隔离开的种群又返回到同一个地方，这些行为特点仍可能保持端始种分离，但是这方面的例子仍然十分少见。不过今年，研究人员发现，仅仅是雄性蝴蝶翅膀颜色的简单差异，加上染色体数目的快速变化，就足以使重返一地的蝴蝶保持其特有的种群特征；而夏威夷的蟋蟀只要靠叫声不同就可以保证其差别。在每一个例子里，今天所观察到的物种个数提示这些特性也已导致快速的物种形成，这种速率以前只在非洲丽鱼科鱼类中被观察到。

Other researchers have looked within animals' genomes to analyze adaptation at the genetic level. In various places in the Northern Hemisphere, for example, marine stickleback fish were scattered among landlocked lakes as the last Ice Age ended. Today, their descendants have evolved into dozens of different species, but each has independently lost the armor plates needed for protection from marine predators. Researchers expected that the gene responsible would vary from lake to lake. Instead, they found that each group of stranded sticklebacks had lost its armor by the same mechanism: a rare DNA defect affecting a signaling molecule involved in the development of dermal bones and teeth. That single preexisting variant--rare in the open ocean--allowed the fish to adapt rapidly to a new environment.

其他研究者研究动物的基因组，从基因水平分析环境适应行为的发生。例如，在北半球的许多地方，在上个冰川季结束后，海棘鱼散布于陆地包围的湖里。今天，它们的后代已经进化成许多不同的物种，但是每一种都独立丧失了保护其不受海洋中的捕食者袭击所需的装甲防护。研究者希望不同的湖之间相关的基因有所差别，可是，他们发现每一组搁浅的棘鱼都通过同样的机制失去了它们的装甲：一种罕见的DNA缺陷影响了一个涉及皮内骨和牙齿生长的信号分子，这一个先前存在的变数——在开放的海洋中很少存在——使得鱼可以迅速适应新的环境。

Biologists have often focused on coding genes and protein changes, but more evidence of the importance of DNA outside genes came in 2005. A study of two species of fruit flies found that 40% to 70% of noncoding DNA evolves more slowly than the genes themselves. That implies that these regions are so important for the organism that their DNA sequences are maintained by positive selection. These noncoding bases, which include regulatory regions, were static within a species but varied between the two species, suggesting that noncoding regions can be key to speciation.

生物学家们以前多关心编码基因和蛋白质的变化，但是2005年，基因外的DNA的重要性越来越凸显。研究两种果蝇发现40%到70%的非编码DNA比基因本身进化更慢。这意味着这些区域对于机体如此重要以至于它们的DNA序列通过主动选择来保持。这些非编码碱基，其中包括调节区域，在一个物种中是稳定的，但是在两个物种中有所不同，提示非编码区域对物种形成很关键。

That conclusion was bolstered by several other studies this year. One experimental paper examined a gene called yellow, which causes a dark, likely sexually attractive, spot in one fruit fly species. A separate species has the same yellow gene but no spot. Researchers swapped the noncoding, regulatory region of the spotted species' yellow gene into the other species and produced dark spots, perhaps retracing the evolutionary events that separated the two. Such a genetic experiment might have astonished and delighted Darwin, who lamented in The Origin that "The laws governing inheritance are quite unknown." Not any longer.

这个结论被今年的许多其它研究所支持。一个实验论文研究了一个称为黄色的基因，这个基因导致一种果蝇黑色的，类似性吸引的斑点。另一个物种有同样的黄色基因，但是没有斑点。研究人员将有斑点物种黄色基因的非编码、调节区域换到另一个物种中，产生了黑色斑点，这或许追溯了分离这两种物种的进化事件。这样的基因实验也许会让Darwin震惊和兴奋，因为他在《物种起源》中哀叹的“主宰遗传的法则完全不可琢磨”已经不是事实了。

To your health
对人类健康的影响

Such evolutionary breakthroughs are not just ivory-tower exercises; they hold huge promise for improving human well-being. Take the chimpanzee genome. Humans are highly susceptible to AIDS, coronary heart disease, chronic viral hepatitis, and malignant malarial infections; chimps aren't. Studying the differences between our species will help pin down the genetic aspects of many such diseases. As for the HapMap, its aims are explicitly biomedical: to speed the search for genes involved in complex diseases such as diabetes. Researchers have already used it to home in on a gene for agerelated macular degeneration.

这种进化研究的突破并不仅仅是象牙塔中的练习，它对于改善人类健康状况有巨大应用潜力。以黑猩猩的基因组为例，人类十分易感AIDS，冠心病，慢性病毒性肝炎，以及恶性痢疾；黑猩猩则不然。研究我们和黑猩猩之间基因的差别可以在基因层面控制这一类疾病。而HapMap，它的目标明确是生物医学的：为了加速寻找糖尿病等复杂疾病的相关基因。研究者已经用其导向目标追踪与老年黄斑变性相关的基因。

And in 2005, researchers stepped up to help defend against one of the world's most urgent biomedical threats: avian influenza. In October, molecular biologists used tissue from a body that had been frozen in the Alaskan permafrost for almost a century to sequence the three unknown genes from the 1918 flu virus--the cause of the epidemic that killed 20 million to 50 million people. Most deadly flu strains emerge when an animal virus combines with an existing human virus. After studying the genetic data, however, virologists concluded that the 1918 virus started out as a pure avian strain. A handful of mutations had enabled it to easily infect human hosts. The possible evolution of such an infectious ability in the bird flu now winging its way around the world is why officials worry about a pandemic today.

2005年，研究者开始帮助防范一种全球范围内最紧急的生物医学威胁：禽流感。十月，分子生物学家用阿拉斯加永冻地带已经冻存了将近一个世纪的尸体的样本测序了1918年流感病毒三个未知的基因——那一次瘟疫流行导致两千万至五千万的人口死亡。大多数致命的流感病毒株在动物病毒与一种已存在的人类病毒结合的时候产生。然而，在研究了基因数据之后，病毒学家认为1918年的病毒一开始是一种纯的禽类病毒株，一些变异使得它可以轻易感染人类宿主。 这种鸟类流感可能进化出的感染能力目前正在世界各地飞行，这也是官方对当今禽流感流行忧虑的原因。

A second group reconstructed the complete 1918 virus based on the genome sequence information and studied its behavior. They found that the 1918 strain had lost its dependence on trypsin, an enzyme that viruses typically borrow from their hosts as they infect cells. Instead, the 1918 strain depended on an in-house enzyme. As a result, the reconstructed bug was able to reach exceptionally high concentrations in the lung tissue of mice tested, helping explain its virulence in humans. The finding could point to new ways to prevent similar deadly infections in the future.

另一个小组根据基因组序列信息和病毒行为研究重构了完整的1918年病毒。他们发现1918年的病毒株已经失去了对胰蛋白酶的依赖，这个酶病毒大都在感染细胞的时候向其宿主借用，而1918年的病毒依靠自身的酶。结果，这个重建的病毒可以在实验小鼠的肺组织中达到格外高的浓度，这有助于解释它在人类中的毒性为何如此之强。这个发现指出了今后阻止类似致命感染的新方向。

Darwin focused on the existence of evolution by natural selection; the mechanisms that drive the process were a complete mystery to him. But today his intellectual descendants include all the biologists--whether they study morphology, behavior, or genetics--whose research is helping reveal how evolution works.

Darwin着眼于通过自然选择而存在的进化，对他来说驱动这个过程的机制完全是一个谜。但是今天，他具有知识的后继者包括全部的生物学家——无论他们研究形态学，行为学，或是遗传学——他们的研究有助于揭示进化是如何进行的。

From Science 23 December 2005, Vol. 310. no. 5756, pp. 1878 - 1879

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