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ScienceWeek
SCIENCEWEEK
October 27, 2006
Vol. 10 - Number 43
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At the last dim horizon, we search among ghostly errors of observations for landmarks that are scarcely more substantial. The search will continue. The urge is older than history. It is not satisfied and it will not be suppressed.
-- Edwin Hubble (1889-1953)
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Contents
(full reports below):
1. Neuroscience: On Form and Function in Systems Neuroscience. "Form follows function" is an architectural philosophy attributed to the great American architect Louis Sullivan (1), and later taken up by the Bauhaus movement. It stresses that the form of a building should reflect its function. Neuroscientists have used the converse of this dictum to learn the functions of neural circuits, believing that if we study...
2. Chemistry: On the Future of Organic Synthesis. The extreme structural diversity found in many natural products poses an extraordinary challenge to chemists trying to synthesize these molecules (1). Many natural products are available only in trace quantities from natural sources, making total or partial synthesis a necessity. For example, the drug Taxol, an anticancer natural product...
3. Astronomy: On Cosmic Rays and the Milky Way. Cosmic rays are extremely high-energy nuclei that travel close to the speed of light. They are ubiquitous in the Milky Way and make up a substantial fraction of the total energy of the Galaxy, equivalent to the energy in large-scale magnetic fields and thermal gases. Their composition largely reflects the natural abundance of the elements in the Galaxy...
4. Palaeoanthropology: On the Last Neanderthals. The last Neanderthals were participants in one of the most dramatic events in the story of human evolution. At a time of increasing climatic instability and environmental deterioration, they would have had to have survived in ever-smaller groups, confined to less environmentally hostile refugia on the coast of the Mediterranean, and competing for access...
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Also Noted:
THE MAKING OF THE FITTEST. DNA and the Ultimate Forensic Record of Evolution. Sean B. Carroll. Norton, New York, 2006. Hardback: 301 pp., illus. $25.95, C$32.50. ISBN 0393061639. More information at:
http://www.amazon.com/exec/obidos/ASIN/0393061639/scienceweek
LIFE. A Journey Through Time. Frans Lanting. Christine Eckstrom, Ed. Taschen, New York, 2006. Hardback: 303 pp., illus. $49.99. ISBN 3822833037. More information at:
http://www.amazon.com/exec/obidos/ASIN/3822833037/scienceweek
FROM LUCY TO LANGUAGE. 2nd ed. Donald Johanson and Blake Edgar. Simon and Schuster, New York, 2006. Hardback: 288 pp., illus. $65, C$83.99. ISBN 0743280644. More information at:
http://www.amazon.com/exec/obidos/ASIN/0743280644/scienceweek
EXPLORATIONS IN MATHEMATICAL PHYSICS. The Concepts Behind an Elegant Language. Don Koks. Springer, New York, 2006. Hardback: 555 pp., illus. $69.95. ISBN 0387309438. More information at:
http://www.amazon.com/exec/obidos/ASIN/0387309438/scienceweek
Special Note: A New Book by the Editor of ScienceWeek:
JUNK SCIENCE. How Politicians, Corporations, and Other Hucksters Betray Us. Dan Agin. Thomas Dunne Books/St. Martin's Press, New York, 2006. Hardback: 336 pp., $24.95. ISBN 0312352417. More information at:
http://www.amazon.com/exec/obidos/ASIN/0312352417/scienceweek
A recent long review of this book appeared in the San Diego Union-Tribune, October 22, 2006. The review can be accessed at:
http://www.signonsandiego.com/uniontrib/20061022/news_lz1v22junk.html
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1. NEUROSCIENCE: ON FORM AND FUNCTION IN SYSTEMS NEUROSCIENCE
The following points are made by W. B. Kristan and P. Katz (Current Biology 2006 16:R828):
1) "Form follows function" is an architectural philosophy attributed to the great American architect Louis Sullivan (1), and later taken up by the Bauhaus movement. It stresses that the form of a building should reflect its function. Neuroscientists have used the converse of this dictum to learn the functions of neural circuits, believing that if we study neural architecture, it will lead us to an understanding of how neural systems function. New tools for studying the structure of neural circuits are being developed, so it is important to discuss what the old techniques have taught us about how to derive function from the form of a neural circuit.
2) The past 30 years have produced breathtaking successes at the two extremes of our knowledge about brain function. At the cellular level, molecular genetics and biophysics have provided explanations of neuronal and synaptic function that are complete and satisfying, from the molecular structure of ion channels to the mechanisms of synaptic release and plasticity. At the other extreme, brain imaging techniques — primarily functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) — have made possible investigations of our own cognitive functions so that we can begin to catch glimpses of such processes as perception, making judgments, paying attention, and thinking. This raises the hope that we will one day understand the mind as completely as we now understand the synapse. To have such an unbroken knowledge from molecules to the mind, however, we will need to understand the large gap in between: how do networks of neurons operate to produce behavior? This intermediate realm, usually called systems neuroscience (2), has a long and hallowed tradition with many current practitioners, but its progress has been slow, in part perhaps because the work is so laborious given the available techniques. Systems-level explanations tend to be complicated, incomplete and often specific to the brain region or the organism being studied.
3) If the excitement buzzing around a recent meeting (Neuronal Circuits: From Structure to Function Meeting, Cold Spring Harbor Laboratory, New York, March 9–12, 2006) is any indication, however, all this is changing. This meeting centered around the question: how much can be learned about the function of a neuronal circuit from its anatomical architecture? The discussions focused mainly on new techniques for determining neuronal connectivity using molecular genetics and imaging. Not surprisingly, with this emphasis, the animals primarily represented were the ones whose genetics are best developed: the fruit fly Drosophila melanogaster, the nematode Caenorhabditis elegans, the zebra fish Danio rerio and the mouse Mus musculus, though these techniques can also be applied in animals that are not genetic models, such as primates, through the use of viral vectors (3). But there is a big question surrounding this work: does the connectivity of a neuronal circuit adequately explain how it functions?
4) Consider, for instance, the elegantly simple central nervous system of C. elegans; with only 302 neurons in its entire nervous system, it is considerably less complicated than a slice of cortex. Every connection in the C. elegans nervous system has been obtained from serial electron microscopy 20–30 years ago. Yet, despite this exquisitely detailed knowledge, not a single behavior has been successfully inferred from looking at the connectivity pattern alone. Killing individual neurons using lasers or molecular genetics has helped the effort greatly, but we do not know the activity patterns of each of the neurons because their extremely small size has made electrophysiological recordings extremely difficult. So, if we could determine the pattern of activity, would we understand how the circuits function? Not necessarily, given the experience of researchers in other systems.(4,5)
References (abridged):
1. Sullivan, L.H. (1896). The tall office building artistically considered. In: Twombly, Robert (Ed.), Lippincott's Magazine. Reprinted in Sullivan, Louis The Public Papers. (1988). (1896). University of Chicago Press, Chicago, IL.
2. Grant, S.G. (2003). Systems biology in neuroscience: bridging genes to cognition. Curr. Opin. Neurobiol. 13, 577-582.
3. Callaway, E.M. (2005). A molecular and genetic arsenal for systems neuroscience. Trends Neurosci. 28, 196-201.
4. Graham Brown, T. (1911). The intrinsic factors in the act of progression in the mammal. Proc. R. Soc. Lond. B 84, 308-319.
5. Marder, E., and Calabrese, R.L. (1996). Principles of rhythmic motor pattern generation. Physiol. Rev. 76, 687-717.
Current Biology http://www.current-biology.com
ScienceWeek http://scienceweek.com
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2. CHEMISTRY: ON THE FUTURE OF ORGANIC SYNTHESIS
The following points are made by Peter Kündig (Science 2006 314:430):
1) The extreme structural diversity found in many natural products poses an extraordinary challenge to chemists trying to synthesize these molecules (1). Many natural products are available only in trace quantities from natural sources, making total or partial synthesis a necessity. For example, the drug Taxol, an anticancer natural product, is present only in minute quantities in the bark of Taxus brevifolia. A closely related compound, 10-deacetylbaccatin III, can be extracted from leaf clippings from Taxus baccata with no harm to the tree (2). During studies of the transformation of 10-deacetylbaccatin into Taxol, a compound was synthesized that turned out to be more soluble and twice as active as Taxol itself (3). This compound was developed into the drug Taxotere. Total and partial syntheses of bioactive natural products and derivatives also provide the driving force for the invention of new reactions with ever-increasing levels of efficiency and selectivity.
2) The synthesis of complex molecules requires patience, stamina, and a profound knowledge of reaction mechanisms. (4) Even for moderately complex molecules, it is not uncommon to require at least 10 steps and sometimes many more. Side reactions produce waste, reduce efficiency, and result in a sharp drop of available material after only a few synthetic steps. Tuning of reactions, work-up, and purifications are all extremely time-consuming. Such syntheses bring to light the limitations of current chemical transformations. The drive for shorter and more efficient synthesis procedures will continue to challenge the resourcefulness of synthetic chemists.
3) Chemists have developed numerous methods to address these challenges and facilitate natural product syntheses. Major advances in catalytic applications have been made. Stable, readily synthesized ruthenium and molybdenum catalysts that allow the exchange of substituents between different olefins (metathesis; 2005 Nobel Prize in chemistry to Y. Chauvin, R. H. Grubbs, and R. R. Schrock) are now routinely used in organic synthesis. Chiral amines have been rediscovered as catalysts, and very elegant, asymmetric, and useful synthetic methods have emerged (5). New, more efficient variants of classical metal-catalyzed carbon-carbon coupling reactions allow alkyl coupling and aryl chloride coupling reactions under mild conditions. Bifunctional catalysis and tandem and multistep catalytic processes all convert very simple small molecules in a series of reactions into highly functionalized complex molecules, and these processes have become prominent. Directed evolution of enzymes for synthesis and the combination of metal-catalyzed reactions with enzymes are also very promising developments.
4) Combinatorial approaches and high-throughput experimentation are also firmly established. They are complemented by the synthesis of self-adaptive combinatorial libraries. The need for cleaner, more sustainable chemical practices also poses new challenges. Environmentally benign chemistry and sustainable processes require new ways of carrying out synthesis. Hence, in addition to the development of new reactions, reagents, and catalysts, novel ways to assemble molecules are an important driver for organic synthesis. Automated synthesis, in which robots and machines carry out much of the tedious bench work, has made its entry into research laboratories. The substitution of conventional work-up, isolation of products, and separation of catalysts and reagents by new techniques is of major importance. Very promising steps in this direction are now in hand.
References (abridged):
1. I. Markó, Science 294, [1842] (2001).
2. S. Zard, Angew. Chem. Int. Ed. 45, 2496 (2006).
3. D. Guénard, F. Guéritte-Voegelein, P. Potier, Acc. Chem. Res. 26, 160 (1993).
4. First European Chemistry Congress, 27 to 31 August 2006, Budapest, Hungary (www.euchems-budapest2006.hu).
5. G. Lelais, D. W. C. MacMillan, Aldrichim. Acta 39, 79 (2006).
Science http://www.sciencemag.org
ScienceWeek http://scienceweek.com
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3. ASTRONOMY: ON COSMIC RAYS AND THE MILKY WAY
The following points are made by Marc Duldig (Science 2006 314:429):
1) Cosmic rays are extremely high-energy nuclei that travel close to the speed of light. They are ubiquitous in the Milky Way and make up a substantial fraction of the total energy of the Galaxy, equivalent to the energy in large-scale magnetic fields and thermal gases. Their composition largely reflects the natural abundance of the elements in the Galaxy, mostly protons (hydrogen nuclei), some alpha particles (helium), and a tiny fraction of the heavier elements. Being charged particles, they are deflected when crossing magnetic fields, but the amount of deflection is dependent on their momentum. The cosmic-ray flux at energies high enough to undergo minimal deflection is so small that sources have proved impossible to observe directly. New work (1) reports the direct observation of an excess signal in cosmic rays coming from the Cygnus region of the sky using a detector array in Tibet. This excess could be either cosmic rays of very high energy or high-energy gamma rays that would likely be associated with cosmic-ray sources. Furthermore, they have also shown that the cosmic-ray gas at these very high energies is rotating with the local spiral arm of the Galaxy, confirming behavior previously only seen at lower energies with cosmic rays influenced by the Sun's extended magnetic field.
2) The difficulty in achieving such observations can be most readily understood when we look at the full cosmic-ray spectrum. The spectrum is approximately a power law, but there are features within it that mark probable changes in the sources. Below about 10^(15) eV, they are almost certainly produced in the shocks from supernovae, but at higher energies there is a steepening in spectrum and a change in the relative elemental abundances, indicating changing source mechanisms. There are further changes in composition at the "ankle", and the origin of particles at the highest energies observed is problematic.
3) At the lowest energies, the cosmic rays are plentiful but are heavily influenced by the solar magnetic field, which is carried beyond the planetary orbits [100 astronomical units (AU) or more, where 1 AU is the mean Earth-Sun distance, or about 1.5 x 10^(8) km] by the gusty plasma wind that emerges from the Sun (the solar wind). This field is complex and dynamic, with shocks propagating from active regions on the Sun and an outer boundary shock that defines the region known as the heliosphere. Low-energy cosmic rays entering the heliosphere lose any information about their arrival direction in reaching the inner solar system as a result of substantial deflections and scatterings.
4) The motion of cosmic rays in a magnetic field is described by a transport equation that takes into account the convection, diffusion, drift, and adiabatic energy loss (if the field is converging) or gain (if the field diverges). This equation was first described by Parker (2,3) and, in the case of the heliosphere, further developed by others such as Forman and Gleeson (4). The equation predicts that the lower-energy cosmic-ray gas should move with the Sun's magnetic field, which rotates with the Sun with a 27-day period. Such behavior is called corotation. Corotation has been observed for many years in lower-energy observations (less than 5 x 10^(10) eV) and causes the largest long-term anisotropy observed in this energy range (5).
References:
1. M. Amenomori et al., Science 314, 439 (2006).
2. E. N. Parker, Planet. Space Sci. 12, 735 (1964).
3. E. N. Parker, Planet. Space Sci. 13, 9 (1965).
4. M. A. Forman, L. J. Gleeson, Astrophys. Space Sci. 32, 77 (1975).
5. D. L. Hall, M. L. Duldig, J. E. Humble, Space Sci. Rev. 78, 401 (1996).
Science http://www.sciencemag.org
ScienceWeek http://scienceweek.com
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4. PALAEOANTHROPOLOGY: ON THE LAST NEANDERTHALS
The following points are made by E. Delson and K. Harvati (Nature 2006 443:762):
1) The last Neanderthals were participants in one of the most dramatic events in the story of human evolution. At a time of increasing climatic instability and environmental deterioration, they would have had to have survived in ever-smaller groups, confined to less environmentally hostile refugia on the coast of the Mediterranean, and competing for access to resources with modern humans pressing on their territory. These conditions are widely thought to have led to the Neanderthals' extinction within a relatively short time after the colonization of Europe by modern humans (1). But new work (2) revises that model considerably. The new work produces dating results from Gorham's Cave, Gibraltar, that might indicate that a group of Neanderthals survived extinction in this part of southern Iberia until at least 28,000 years ago -- thousands of years after anatomically modern humans had firmly established themselves as the inheritors of the European continent.
2) Neanderthals inhabited western Eurasia from a time in the Middle Pleistocene between 500,000 and 160,000 years ago [depending on the definition of the earliest members of the Neanderthal group (3,4)] until approximately 30,000 years ago. They were characterized by a suite of specialized morphological features, many of them unique to the group, that together make them highly distinct from modern humans. Their skeletal remains are often found associated with "Mousterian" stone tools, named after the Le Moustier site in France. In Europe -- but not in northwest Africa or southwest Asia -- such tools are exclusively found with Neanderthals, and are presumed to have been made by them.
3) The find of Finlayson et al (2) of Mousterian tools in Gorham's Cave, Gibraltar, might be the most recent indication of Neanderthal settlement yet. Zafarraya (Spain) and Figueira Brava (Portugal) have yielded southern Iberian putative late Neanderthal fossils, whereas St. Césaire and Arcy-sur-Cure (both France) are slightly older (between 35,000 and 30,000 years old). Also indicated are Le Moustier, the eponymous site for the Mousterian tool industry, and Feldhofer, the site of the initial Neander Valley find of 1856. Vindija (Croatia) and Mezmaiskaya (Russia) are noted by Finlayson et al (2) as having recently been redated to older than 30,000 years ago. Subalyuk (Hungary), Guattari (Italy), Amud (Israel) and Shanidar (Iraq), as well as Feldhofer and Le Moustier, are older than 35,000 years, but they give an indication of the geographical range of the last glacial Neanderthal finds; sites farther east, such as Teshik-Tash, have recently been the subject of questions as to the identity of the fossils recovered.
4) Neanderthal remains discovered from times near the end of their existence are sometimes found with tool assemblages resembling those produced by early modern humans. This is possibly a result of acculturation or imitation of modern human technology (5). Although there is still some discussion over the Neanderthals' taxonomic status and their relationship to modern humans, it is now widely recognized that they represent a distinct, Eurasian evolutionary lineage. They shared a common ancestor with modern humans in the early Middle Pleistocene or before (3), but became isolated thereafter from the rest of the Old World. Glacial climatic conditions are considered at least in part responsible for this isolation and for the evolution of some distinctive features of Neanderthal morphology, especially their short limbs and heavy trunks. These are similar to, but more extreme than, features of cold-adapted modern populations such as the Inuit.
References (abridged):
1. Mellars, P. Nature 439, 931-935 (2006).
2. Finlayson, C. et al. Nature 443, 850-853 (2006).
3. Delson, E. & Baab, K. in McGraw-Hill Encyclopedia of Science and Technology Vol. 7, 464-478 (in the press).
4. Harvati, K. & Harrison, T. (eds) Neanderthals Revisited: New Approaches and Perspectives (Springer, Dordrecht, in the press).
5. Harrold, F. B. in The Human Revolution: Behavioural and Biological Perspectives on the Origins of Modern Humans (eds Mellars, P. & Stringer, C.) 677-713 (Princeton Univ. Press, 1989).
Nature http://www.nature.com/nature
ScienceWeek http://scienceweek.com
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