Volume 441 Number 7094 pp667-784 (8 June 2006) 封面故事：“太古代”地球上存在生命的证据“太古代”（距今25亿年前）地球上是否存在生命一直是一个激烈争论的问题。这种争论在很大程度上集中在被称为“叠层石”(stromatolites)的分层沉积结构是否像今天那样反映群居微生物的活动或反映一些非生物过程。现在，对澳大利亚西部一个引人注目的10公里长的裸露岩层所做的一项新的分析，为认为那个时候地球上存在生命的观点提供了支持。这里的“叠层石”已有大约34.30亿年，显示出与在较年轻的微生物礁石中发现的“叠层石”类似的特点：它不是一系列彼此孤立的化石，却更像以化石形势存在的一个完整的生态系统。看来，那个时候地球上不但存在生命，而且生命还很兴旺。封面图片所示为一个来自裸露礁石的锥形“叠层石”：虽然没有刻度标尺，但从Nature杂志标识底下来看其留下的阴影，就能知道它有多大。（摄影：A. Allwood） （Article p. 716; News and Views）
前港督彭定康高论欧洲竞争力曾在高等教育和科学研究方面居支配地位的欧洲，有变成落败者的危险。这是前欧盟负责外部事物的专员、现任英国两所大学校长的彭定康的观点。在一篇“评论”文章中，他解释说，他并没有看到旨在使欧盟在2010年前成为世界上最有竞争力的知识经济体系的“里斯本战略”有什么希望。市场经济不能支持知识和学习所需的必要投资，而没有这种投资，欧洲在竞争全球市场、声望和政治影响的过程中将落在美国、中国和其他亚洲国家后面。
碳在恒星周围气体稳定性中所起的作用我们附近的年轻恒星b-Pictoris周围的侧向圆盘是一个原型“碎片盘”，由固体行星类天体解体后所产生的物质组成，而这些行星类天体可能曾经与太阳系的彗星和小行星相似。以前的研究工作得出的结论是，该恒星周围的气体应被迅速吹走，这与观测结果是相反的。来自NASA的FUSE卫星的新的远红外数据，为这种矛盾提供了一个可能的解释：该圆盘的气体碳含量极高，这使得它很稳定，不会被吹走。
描述粒状物质流动状态的新模型描述粒状物质怎样在剪切力作用下运动的方程式仍然是一个有争论的问题。Jop等人现在提出一个新模型，来解释三维体系中致密的颗粒流。他们的模型受到牙膏等粘塑性流体的行为的启发。该模型研究的结果可以成为地球物理或工业应用中模拟复杂流动的一个基础工具。
碳在恒星周围气体稳定性中所起的作用我们附近的年轻恒星b-Pictoris周围的侧向圆盘是一个原型“碎片盘”，由固体行星类天体解体后所产生的物质组成，而这些行星类天体可能曾经与太阳系的彗星和小行星相似。以前的研究工作得出的结论是，该恒星周围的气体应被迅速吹走，这与观测结果是相反的。来自NASA的FUSE卫星的新的远红外数据，为这种矛盾提供了一个可能的解释：该圆盘的气体碳含量极高，这使得它很稳定，不会被吹走。
含有扭曲氨基键的化合物的合成氨基-氨基键在化学和生物中很普遍。在非环化合物中，氨基键经常是平面的。然而，在双环“桥头堡”内酰胺中，氨基官能团是高度扭曲的，1938年捷克化学家Rudolf Lukes的一篇著作引起人们对这些“扭曲的氨基”的有趣性质的注意。有趣倒是有趣，但要生成它们却很难。现在，Kousuke Tani 和 Brian Stoltz报告了他们对一种含有一个扭曲的氨基键的化合物的首次明确的合成、分离和X-射线晶体定性。他们的合成方法避开了形成氨基键的传统路径，而用这种方法合成的化合物的获得将使我们对氨基键的性质有更深了解。
动态应力在余震中的作用得到证实余震是最常见的地震类型，过去被认为是由早先的一次“主震”诱导的静态应力诱发的。最近的研究工作说明，动态应力或晃动也可能是一个因素，而对1984-2002年南加州地震目录上的地震位置所做的一项分析研究证实了该观点。对余震密度随距主震距离而减小的情况所做的精密测量显示，余震的概率与在0.2公里至50公里处的地震晃动的最大幅度是一致的。
蜥脚类恐龙也有矮小种类认为矮的物种往往在岛屿种群中演化的观点，最近在关于弗洛瑞斯人(Homo floresiensis)和在弗洛瑞斯岛上发现的矮小动物（主要是大象）的讨论中受到很多关注。现在，似乎同样的事情也曾发生在蜥脚类恐龙身上。在德国北部新发现的化石已被鉴定为是矮小成年蜥脚类恐龙，可能是在下萨克森盆地的岛屿上从它们体形更大的大陆同类演化来的。以前，蜥脚类恐龙被认为几乎都是很大的，它们包括“梁龙”（Diplodocus）和“无法龙”（Titanosaurus），而所有较小的蜥脚类恐龙骨头都被假设为来自未成年的个体。在这些新发现的化石中，是骨头组织学研究证明了它们是成年个体的。
所有脊椎动物的咽结构的确都同源神经脊细胞（Neural crest cells）是脊椎动物的一个定义特点，它们在胚胎中确定脸部、头部的很多地方、以及咽部或腮部的特征。然而，在被称为七鳃鳗的原始无颚脊椎动物身上，咽的结构与有颚脊椎动物很不相同，这便提出了关于神经脊细胞在同源结构的成形中扮演什么角色的问题。用SoxE基因（该基因确定脊椎动物的头部形状）的定向错误表达所做的一个实验证实，它们在七鳃鳗身上起类似作用。所以，不管结构上有什么不同，所有脊椎动物的咽结构的确都是同源的。
大脑蘑菇体在睡眠调控中的作用果蝇是睡眠研究的一个成熟的遗传模型。果蝇具有与我们称之为睡眠的行为相似的行为模式，但睡眠典型的标志性EEG变化及其阶段尚没有被识别出来，所以不可能说果蝇的睡眠是否是一个神经过程，以及如果是，涉及到什么神经基质。回答这一问题，是解释基因影响睡眠的机制的一个重要步骤。现在，两个小组已经解决了这一问题，他们都识别出，被称为蘑菇体的结构是大脑参与睡眠调控的部分。这一发现使我们从神经角度对果蝇的睡眠有了一个认识，并且还将睡眠与蘑菇体的其他已知功能——学习和记忆联系了起来。
皮层神经通信的另一种机制大脑皮层的神经元之间的迅速通信，涉及一个动作电位的传播，但关于这个动作电位是皮层神经通信的惟一形式的假设却可能需要修正。整细胞记录表明，可能存在另一种机制。膜电位的变化，如与轴突活动相关的膜电位变化，也可能沿轴突传播，并可明显改变联会后电位的平均幅度。这种类型的神经信号可能有重要后果，如在感官刺激、清醒到睡眠的过渡、以及癫痫发作等条件下，膜电位会发生很大变化。
ContentsEditorials
Econophysicists matter p667
Economics and physics are two disciplines that, contrary to widespread perceptions, have significant common agendas. Shame, then, that the professionals don't do more to recognize the fact.
doi:10.1038/441667a
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Brute force in the clinic p667
Clinical microbiologists should catch up with their colleagues and use metagenomics.
doi:10.1038/441667b
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Peer review on trial p668
Introducing two Nature initiatives.
doi:10.1038/441668a
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Research Highlights
Research highlights p670
doi:10.1038/441670a
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News
EU science fund targets young guns p672
European Research Council becomes a reality.
Alison Abbott
doi:10.1038/441672a
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Disasters drive DNA forensics to reunite families p673
Genetics innovations may help Holocaust survivors.
Claire Ainsworth
doi:10.1038/441673a
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Insurers' disaster files suggest climate is culprit p674
Rising costs hint at weather effect.
Quirin Schiermeier
doi:10.1038/441674a
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Politicians chastise Australia's science institute p674
The CSIRO's management answers critics.
Carina Dennis
doi:10.1038/441674b
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Sea-lion studies come to a halt after court judgement p677
US government blocks 'hot branding' of pups.
Rex Dalton
doi:10.1038/441677a
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Sidelines p677
doi:10.1038/441677a
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Online methods share insider tricks p678
Wiki-style website allows tinkering with lab protocols.
Helen Pearson
doi:10.1038/441678a
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US scraps plan to license foreign scientists p679
Geoff Brumfiel
doi:10.1038/441679a
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News in brief p680
doi:10.1038/441680a
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Correction p681
doi:10.1038/441681a
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News Features
Virology: The gene weavers p683
Viruses are often thought of as simple creatures. But their staggering diversity and genetic promiscuity could make them the most creative force in evolution, says Garry Hamilton.
doi:10.1038/441683a
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Econophysics: Culture Crash p686
Some economists had hoped that physicists might shake up the rigid theories typical of mainstream economics. But so far, they're unimpressed by physicists' handling of the markets. Philip Ball reports.
doi:10.1038/441686a
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Business
Biochemist strikes gold p689
Merck is tapping into academic research in its hunt for drug candidates. Meredith Wadman reports on the company's latest deal with Harvard.
Meredith Wadman
doi:10.1038/441689a
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Correspondence
Funding: income criterion would hit postdoc careers p690
Phil Bland
doi:10.1038/441690a
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Funding: proposals ignore mentoring and teaching p690
John Bothwell
doi:10.1038/441690b
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Funding: income is already dependent on outcome p690
Joanna Bryson
doi:10.1038/441690c
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Technology transfer is all about bringing in money p690
W. Graham Richards
doi:10.1038/441690d
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Debye's wooden response undercut Nazi orders p690
Harvey Posvic
doi:10.1038/441690e
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Commentary
Europe pays the price for spending less p691
Europe's contribution to the global advancement of science and the promotion of learning is in decline. Better funding of universities and research institutions is needed to reverse this trend, argues Christopher Patten.
doi:10.1038/441691a
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Books and Arts
From cell to organism p695
How genetics unlocked the mysteries of development.
Alfonso Martinez Arias reviews Coming to Life: How Genes Drive Development by Christiane Nüsslein-Volhard
doi:10.1038/441695a
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Charting an Arabic course p696
A. M. Celâl engör reviews Mathematical Geography and Cartography in Islam and their Continuation in the Occident, Vol. I. Historical Presentation by Fuat Sezgin, translated by Guy Moore and Geoff Sammon
doi:10.1038/441696a
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Theatre: Would the real Mr Feynman...? p697
Richard Webb reviews Clever Dick written and directed by Crispin Whittell
doi:10.1038/441697a
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The eye of the beholder p697
Richard Gregory reviews On Seeing: Things Seen, Unseen and Obscene by F. Gonzalez-Crussi
doi:10.1038/441697b
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News and Views
Chemistry: Synthesis with a twist p699
Amide bonds underpin protein stability, but distortion from their preferred geometry makes them reactive. An archetypal twisted amide has at last been made, and its chemistry will be revelatory.
Harry H. Wasserman
doi:10.1038/441699a
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Palaeontology: Respect for stromatolites p700
Is it time to stop worrying over whether the ancient structures called stromatolites are of microbial origin? 'Yes' is the answer to emerge from field and lab work on a 3,430-million-year-old marine ecosystem.
Stanley M. Awramik
doi:10.1038/441700a
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Photonics: Transparency on an optical chip p701
A two-laser trick that renders opaque media transparent can be achieved in systems of tiny optical resonators — with potentially profound consequences for optical communication and information processing.
Robert W. Boyd and Daniel J. Gauthier
doi:10.1038/441701a
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Neurobiology: Extending influence p702
Rather than merely firing in a digital on–off fashion, vertebrate neurons may have an analogue aspect to their signalling too — a finding that will not surprise many who have worked on invertebrate neurons.
Eve Marder
doi:10.1038/441702a
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Earthquakes: A hand on the aftershock trigger p704
Received wisdom relates that static stress change associated with an earthquake mainshock is the prime mover of its aftershocks. But a fresh look at the data points the finger at wave-surfing dynamic stress.
Ian Main
doi:10.1038/441704a
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Chemical technology: All together now p705
A method that combines techniques for performing chemical synthesis, separation and measurement on a single device illustrates the considerable potential of integrated lab-on-a-chip technology.
Stephen J. Haswell
doi:10.1038/441705a
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Brief Communications
Biodiversity hotspots: Rediscovery of the world's leggiest animal p707
This ancient animal, found only in a tiny stretch of California, is close to being a true millipede.
Paul E. Marek and Jason E. Bond
doi:10.1038/441707a
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Brief Communications Arising
Molecular spectroscopy: Complexity of excited-state dynamics in DNA pE7
Dimitra Markovitsi, Francis Talbot, Thomas Gustavsson, Delphine Onidas, Elodie Lazzarotto and Sylvie Marguet
doi:10.1038/nature04903
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Molecular spectroscopy: Complexity of excited-state dynamics in DNA (Reply) pE8
Carlos E. Crespo-Hernández, Boiko Cohen and Bern Kohler
doi:10.1038/nature04904
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Articles
Titan Radar Mapper observations from Cassini's T3 fly-by p709
C. Elachi, S. Wall, M. Janssen, E. Stofan, R. Lopes, R. Kirk, R. Lorenz, J. Lunine, F. Paganelli, L. Soderblom, C. Wood, L. Wye, H. Zebker, Y. Anderson, S. Ostro, M. Allison, R. Boehmer, P. Callahan, P. Encrenaz, E. Flamini, G. Francescetti, Y. Gim, G. Hamilton, S. Hensley, W. Johnson, K. Kelleher, D. Muhleman, G. Picardi, F. Posa, L. Roth, R. Seu, S. Shaffer, B. Stiles, S. Vetrella and R. West
doi:10.1038/nature04786
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Stromatolite reef from the Early Archaean era of Australia p714
Abigail C. Allwood, Malcolm R. Walter, Balz S. Kamber, Craig P. Marshall and Ian W. Burch
doi:10.1038/nature04764
Abstract | Full Text | PDF (277K) | Supplementary information
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Noise-resistant and synchronized oscillation of the segmentation clock p719
Kazuki Horikawa, Kana Ishimatsu, Eiichi Yoshimoto, Shigeru Kondo and Hiroyuki Takeda
doi:10.1038/nature04861
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Letters
Stabilization of the disk around Pictoris by extremely carbon-rich gas p724
Aki Roberge, Paul D. Feldman, Alycia J. Weinberger, Magali Deleuil and Jean-Claude Bouret
doi:10.1038/nature04832
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A constitutive law for dense granular flows p727
Pierre Jop, Yoël Forterre and Olivier Pouliquen
doi:10.1038/nature04801
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Synthesis and structural analysis of 2-quinuclidonium tetrafluoroborate p731
Kousuke Tani and Brian M. Stoltz
doi:10.1038/nature04842
First paragraph | Full Text | PDF (249K) | Supplementary information
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Decay of aftershock density with distance indicates triggering by dynamic stress p735
K. R. Felzer and E. E. Brodsky
doi:10.1038/nature04799
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Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur p739
P. Martin Sander, Octávio Mateus, Thomas Laven and Nils Knötschke
doi:10.1038/nature04633
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Intensity of sexual selection along the anisogamy–isogamy continuum p742
Adam Bjork and Scott Pitnick
doi:10.1038/nature04683
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Social interactions among epithelial cells during tracheal branching morphogenesis p746
Amin S. Ghabrial and Mark A. Krasnow
doi:10.1038/nature04829
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Importance of SoxE in neural crest development and the evolution of the pharynx p750
David W. McCauley and Marianne Bronner-Fraser
doi:10.1038/nature04691
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A dynamic role for the mushroom bodies in promoting sleep in Drosophila p753
Jena L. Pitman, Jermaine J. McGill, Kevin P. Keegan and Ravi Allada
doi:10.1038/nature04739
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Sleep in Drosophila is regulated by adult mushroom bodies p757
William J. Joiner, Amanda Crocker, Benjamin H. White and Amita Sehgal
doi:10.1038/nature04811
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Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential p761
Yousheng Shu, Andrea Hasenstaub, Alvaro Duque, Yuguo Yu and David A. McCormick
doi:10.1038/nature04720
First paragraph | Full Text | PDF (1,370K) | Supplementary information
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Germline transmission of genetically modified primordial germ cells p766
Marie-Cecile van de Lavoir, Jennifer H. Diamond, Philip A. Leighton, Christine Mather-Love, Babette S. Heyer, Renee Bradshaw, Allyn Kerchner, Lisa T. Hooi, Terri M. Gessaro, Susan E. Swanberg, Mary E. Delany and Robert J. Etches
doi:10.1038/nature04831
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SAGA interacting factors confine sub-diffusion of transcribed genes to the nuclear envelope p770
Ghislain G. Cabal, Auguste Genovesio, Susana Rodriguez-Navarro, Christophe Zimmer, Olivier Gadal, Annick Lesne, Henri Buc, Frank Feuerbach-Fournier, Jean-Christophe Olivo-Marin, Eduard C. Hurt and Ulf Nehrbass
doi:10.1038/nature04752
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Nuclear pore association confers optimal expression levels for an inducible yeast gene p774
Angela Taddei, Griet Van Houwe, Florence Hediger, Veronique Kalck, Fabien Cubizolles, Heiko Schober and Susan M. Gasser
doi:10.1038/nature04845
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Naturejobs
Prospect
Prospect p779
Hustling for opportunities can overcome local disadvantages.
Paul Smaglik
doi:10.1038/nj7094-779a
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Region
Bound for Boston p780
With its top academic institutions, Boston has long been a Mecca for biotechnology companies. But the demand for more academic input into industrial science is luring top drug companies there too, says Corie Lok.
Corie Lok
doi:10.1038/nj7094-780a
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Careers and Recruitment
Bruce Jones, chief scientist, United States Geological Survey, Washington DC p782
Snake man heads for the Environmental Protection Agency.
Virginia Gewin
doi:10.1038/nj7094-782a
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Nurturing bioincubators in the north p782
Sheffield boosts bioscience.
Gene Russo
doi:10.1038/nj7094-782b
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Einstein's secret diary? p782
A day in the life of a grad student.
Mhairi Dupré
doi:10.1038/nj7094-782c
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Futures
The computiful game p784
A sporting chance.
Paul Steven Miller
doi:10.1038/441784a
Full Text | PDF (230K)
See also: Editor's summary
