ScienceWeek

SCIENCEWEEK

September 15, 2006

Vol. 10 - Number 37

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Back issues of ScienceWeek can be searched for subjects, names, terms, etc. at: http://scienceweek.com/swfr.htm

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Every great scientific truth goes through three stages. First, people say it conflicts with the Bible. Next they say it had been discovered before. Lastly they say they always believed it.

-- Louis Agassiz (1807-1873)

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Contents (full reports below):

1. Evolution: On Sex Ratios and Social Evolution.
When we think of modern biology, an image that does not usually come to mind is of an entomologist squinting over mounds of wasps, sorting out the males from the females, and assiduously tallying them up. This work requires no fancy machines, no chemicals, no molecular techniques. But what it does rest on is a theory, and such seemingly pedestrian work...

2. Psychology: On Human Consciousness.
"Is she understanding my words and feeling my caresses?" is a question constantly asked by relatives and caregivers of comatose and vegetative state patients in intensive care units throughout the world. Probing residual mental function in such critical situations poses major medical and ethical issues. Our current answers to this question are mainly based on...

3. Fluid dynamics: On the Transience of Turbulence.
Turbulence is not a trivial problem. It influences all manner of physical effects -- aerodynamic drag, cooling and heating, to name just a few. And perhaps its most notorious guise is the worrisome mid-flight buffeting that can so upset air passengers. Yet, for all its ubiquity, scientists, engineers and mathematicians have long struggled to understand...

4. Organic chemistry: On Symmetry-Breaking by Catalysts.
Chirality, the "left-handed" or "right-handed" property of objects that are mirror images of each other, is ubiquitous in the observable world -- shoes, conch shells, wood screws and umbilical cords, for instance. This property extends to objects in the nanoscale dimension; nearly all molecules in nature (such as amino acids, sugars, alkaloids and...

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Also Noted:

Egypt: How a Lost Civilisation Was Rediscovered. Joyce Tyldesley. University of California Press, Berkeley, 2006. Hardback: 256 pp., illus. $24.95. ISBN 0520250206. More information at: http://www.amazon.com/exec/obidos/ASIN/0520250206/scienceweek

The Theoretical Biologist's Toolbox: Quantitative Methods for Ecology and Evolutionary Biology. Marc Mangel. Cambridge University Press, Cambridge, 2006. Paperback: 389 pp., illus. $50. ISBN 0521537487. More information at: http://www.amazon.com/exec/obidos/ASIN/0521537487/scienceweek

What the Doctor Didn't Say: The Hidden Truth about Medical Research. Jerry Menikoff, with Edward P. Richards. Oxford University Press, New York, 2006. Hardback: 335 pp., illus. $29.95. ISBN 0195147979. More information at: http://www.amazon.com/exec/obidos/ASIN/0195147979/scienceweek

Geek Logik: 50 Foolproof Equations for Everyday Life. Garth Sundem. Workman, New York, 2006. Hardback: 119 pp. $12.95, C$16.95. ISBN 0761140212. More information at: http://www.amazon.com/exec/obidos/ASIN/0761140212/scienceweek

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1. EVOLUTION: ON SEX RATIOS AND SOCIAL EVOLUTION

The following points are made by David C. Queller (Current Biology 2006 16:R664):

1) When we think of modern biology, an image that does not usually come to mind is of an entomologist squinting over mounds of wasps, sorting out the males from the females, and assiduously tallying them up. This work requires no fancy machines, no chemicals, no molecular techniques. But what it does rest on is a theory, and such seemingly pedestrian work has tested and confirmed one of the most elegant and successful theories in modern biology.

2) The ratio of females to males in a species is a topic that interested Darwin, but how such ratios evolve left him puzzled. The basic solution to the problem has led to a body of work that has informed nearly every important area of social evolution: group selection, kin selection, parent–offspring conflict, evolutionary stable strategies and game theory, and within-genome conflict.

3) The solution of the sex ratio problem has traditionally been attributed to Sir Ronald A. Fisher's 1930 classic, THE GENETICAL THEORY OF NATURAL SELECTION. But it is now known that a German biologist, Carl Düsing, got the solution more than four decades earlier. Fisher's book was the pipeline through which the theory flowed into the modern era, but his research reputation will now have to rest on other accomplishments, such as inventing the analysis of variance and deriving the fundamental theorem of natural selection.

4) The sex ratio argument, modernized and simplified a bit, goes like this. Natural selection is about reproduction. A gene affecting sex ratio does not affect your number of offspring; it simply shifts those offspring between the categories of male and female. But this allocation can affect your number of grandchildren if sons and daughters have different average reproduction. Düsing's key insight was that the total reproduction of all sons in the population has to equal the total reproduction of all the daughters, which follows from the fact that each grandchild has a father (one of the sons) and a mother (one of the daughters). If we let the total number of grandchildren, sons and daughters in the population be G, S and D, respectively, then the average reproduction of a son is G/S and the average reproduction of daughter is G/D. This means if there are more daughters than sons in the population (D > S), the average daughter will be less successful and mothers will be selected to make more sons. Conversely, if there are more sons than daughters (S > D), their average success will be lower, and selection will favor mothers that produce more daughters. Because the total reproduction of each sex is equal, individuals of the rarer sex have greater average success, and parents who produce more of the rare sex will have more grandchildren. This produces a stable equilibrium at S = D and accounts for the widespread occurrence of 1:1 sex ratios in nature. (1-5)

References (abridged):

1. Boomsma, J.J., and Grafen, A. (1990). Intraspecific variation in ant sex ratios and the Trivers-Hare hypothesis. Evolution 44, 1026-1034

2. Bourke, A.F.G., and Franks, N.R. (1995). Social Evolution in Ants. Princeton University Press, Princeton

3. Charnov, E.L. (1982). The Theory of Sex Allocation. Princeton University Press, Princeton

4. Crozier, R.H., and Pamilo, P. (1996). Evolution of Social Insect Colonies: Sex Allocation and Kin Selection. Oxford University Press, Oxford

5. Edwards, A.W.F. (1998). Natural selection and the sex ratio: Fisher's sources. Am. Nat. 51, 564-569

Current Biology http://www.current-biology.com

ScienceWeek http://scienceweek.com

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2. PSYCHOLOGY: ON HUMAN CONSCIOUSNESS

The following points are made by Lionel Naccache (Science 2006 313:1395):

1) "Is she understanding my words and feeling my caresses?" is a question constantly asked by relatives and caregivers of comatose and vegetative state patients in intensive care units throughout the world. Probing residual mental function in such critical situations poses major medical and ethical issues. Our current answers to this question are mainly based on detailed behavioral and neurological observations, but this approach may be blind to inner active mental processes. Since the late 1980s, several neurophysiological correlates of cognitive processes have been proposed to better assess the existence of this covert mental life (1). This approach has aimed to discriminate among comatose or vegetative state patients those who are still cognitively active. New work (2) uses functional magnetic resonance imaging (fMRI) to infer the psychological processes at work in such patients during mental imagery tasks that do not elicit otherwise observable behavior.

2) The authors studied a 23-year-old woman who sustained a severe traumatic brain injury in a road traffic accident. After an initial comatose state (defined as an unarousable unresponsiveness state), she opened her eyes and demonstrated sleep-wake cycles. However, even during the waking periods, she was unresponsive (for example, to visual or auditory stimuli) and did not manifest spontaneous intentional behaviors. These signs are diagnostic of a vegetative state.

3) In a first experiment conducted 5 months after the accident, Owen and colleagues presented spoken sentences to the patient while recording neural responses with fMRI. Speech-specific brain regions were clearly activated while the patient listened to these sentences, as compared to acoustically matched noise sequences. Moreover, sentences containing ambiguous homophone words (for example, creak/creek) activated an additional left inferior frontal lobe region known to subserve the selection of semantic knowledge among competing alternatives (3). In sharp contrast to her behavior, which was suggestive of poor cognitive abilities, this patient could process external auditory information involving language.

4) In a second experiment, the authors engaged the patient in two mental imagery tasks by asking her either to "imagine visiting the rooms in your home" or to "imagine playing tennis." The result of this second fMRI investigation is quite spectacular. Patterns of brain activation observed during the 30-s period of each task were highly suggestive of an active mental performance relevant to the task. In the spatial mental imagery task, Owen et al observed neural activations within a network including the parahippocampal gyrus, posterior parietal cortex, and lateral premotor cortex. When the patient was asked to imagine playing tennis, strong activations were recorded in the supplementary motor areas that control motor responses.

5) Despite the patient's very poor behavioral status, the fMRI findings indicate the existence of a rich mental life, including auditory language processing and the ability to perform mental imagery tasks. On one hand, this single case makes a strong argument for the development of fMRI and other neurophysiological tools (such as monitoring electroencephalogram brain responses to external stimuli) to evaluate cognition in such patients. On the other hand, we should not generalize from this single patient, who suffered relatively few cerebral lesions, to most other vegetative state patients, who typically have massive structural brain lesions. (3-5)

References (abridged):

1. S. Laureys, F. Perrin, C. Schnakers, M. Boly, S. Majerus, Curr. Opin. Neurol. 18, 726 (2005)

2. A. M. Owen et al., Science 313, 1402 (2006)

3. S. L. Thompson-Schill, M. D'Esposito, I. P. Kan, Neuron 23, 513 (1999)

4. S. Laureys et al., Brain 123, 1589 (2000)

5. N. D. Schiff et al., Brain 125, 1210 (2002)

Science http://www.sciencemag.org

ScienceWeek http://scienceweek.com

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3. FLUID DYNAMICS: ON THE TRANSIENCE OF TURBULENCE

The following points are made by Daniel Perry Lathrop (Nature 2006 443:36):

1) Turbulence is not a trivial problem. It influences all manner of physical effects -- aerodynamic drag, cooling and heating, to name just a few. And perhaps its most notorious guise is the worrisome mid-flight buffeting that can so upset air passengers. Yet, for all its ubiquity, scientists, engineers and mathematicians have long struggled to understand the underlying nature of turbulence. New work (1) stirs things up further with the suggestion that, far from being the steady-state phenomenon it was assumed to be, turbulence does, in fact, disappear --given time.

2) Although fluid turbulence most often occurs because a fluid's nonlinearity is great enough to overcome the effects of viscosity, roughness of surfaces and external shaking can play their part, too: with very smooth walls and in a quiet environment, regular, laminar flows can sometimes persist, even at very high flow rates. Many studies, including the Hof paper (1), focus on this ideal case.

3) Part of the problem in dealing with turbulence in any more practical situation is that its irregular patterns bear little resemblance to the smooth analytical solutions that emerge from the equations of motion that govern fluid flow. For decades, the general view has been that turbulence is merely a nonlinear solution of these equations: turbulence might be just one step beyond chaos, but it forms a well-defined, persistent steady state.

4) Hof et al (1) cast serious doubt on this thesis. Although they focus on flow in a straight pipe, their results may well apply to the broader class of turbulent "shear flows", which are defined by different layers of a fluid moving at different speeds. Such flows include those over cars and aircraft wings and within air ducts, and those used to cool electronics. The authors' observations might also -- more controversially -- apply to certain flows in astrophysics. What all these cases have in common is that it is unclear when turbulence ensues, and why it persists. The authors argue that turbulence started by a gentle kick will eventually decay, no matter how large the nonlinearities in play. A quantity known as the Reynolds number is used to measure the strength of nonlinearity in a flow relative to the smoothing effects of viscosity. Past studies had indicated that shear turbulence could decay at small Reynolds numbers, but that beyond a certain Reynolds number, the turbulence would become permanent (2,3). Not so, say Hof and colleagues (1): shear turbulence is always destined to return to a laminar state -- provided, that is, one waits long enough.(4,5)

References (abridged):

1. Hof, B. , Westerweel, J. , Schneider, T. M. & Eckhardt, B. Nature 443, 59-62 (2006)

2. Faisst, H. & Eckhardt, B. J. Fluid Mech. 504, 343-352 (2004)

3. Peixinho, J. & Mullin, T. Phys. Rev. Lett. 96, 094501 (2006)

4. Ott, E. , Grebogi, C. & Yorke, J. A. Phys. Rev. Lett. 64, 1196-1199 (1990)

5. Balbus, S. A. & Hawley, J. F. Rev. Mod. Phys. 70, 1-53 (1998)

Nature http://www.nature.com/nature

ScienceWeek http://scienceweek.com

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4. ORGANIC CHEMISTRY: ON SYMMETRY-BREAKING BY CATALYSTS

The following points are made by Scott E. Denmark (Nature 2006 443:40):

1) Chirality, the "left-handed" or "right-handed" property of objects that are mirror images of each other, is ubiquitous in the observable world -- shoes, conch shells, wood screws and umbilical cords, for instance. This property extends to objects in the nanoscale dimension; nearly all molecules in nature (such as amino acids, sugars, alkaloids and terpenes) and legions of synthetic compounds are chiral. For chemists who wish to prepare purpose-built compounds with specific attributes -- for example, medicinal, mechanical, physical -- the ability to imbue molecules with the appropriate chirality is paramount. New work (1) describes a method that allows chiral molecules to be generated from achiral precursors. The chiral products are of great use as general building-blocks for further organic synthesis.

2) Chirality is fundamental to the structure, properties and function of molecules. How such molecules interact with one another in recognition, binding and chemical reaction is crucially dependent on their chirality. The synthesis of one chiral form of a molecule -- known as a single enantiomer -- can be achieved by the application of several well-established principles (2). The simplest method is to physically separate equal mixtures of enantiomers, a process known as resolution. Another powerful method is asymmetric synthesis, in which chiral molecules are prepared from achiral precursors by the action of a chiral reagent or catalyst (3). In fact, nature has evolved highly selective enzymes to construct the chiral molecules of life, and these have been adapted for laboratory applications with unnatural substrates (4).

3) An interesting subclass of asymmetric synthesis involves reactions that select between enantiotopic groups in achiral molecules with reflection symmetry. These groups are indistinguishable except in a chiral environment or when acted upon by a chiral agent. A reaction at one of the enantiotopic groups will produce a chiral molecule, whereas the same reaction at its counterpart will produce the opposite enantiomeric product. Certain enzymes (5) and a few synthetic organic catalysts can recognize and functionalize enantiotopic groups in molecules.

4) Zhao et al (1) have now devised a non-biological catalyst that can effect this transformation with synthetically useful trialkylsilyl groups. Temporarily attaching trialkylsilyl groups to sensitive portions of organic molecules is a common strategy to prevent unwanted transformations of reactive chemical groups. The team has amalgamated the utility of the temporary protection strategy with the symmetry-breaking construction of value-added, chiral building-blocks in single enantiomer form.

References (abridged):

1. Zhao, Y. , Rodrigo, J. , Hoveyda, A. H. & Snapper, M. L. Nature 443, 67-70 (2006)

2. Mulzer, J. in Stereoselective Synthesis: Methods of Organic Chemistry (Houben-Weyl) 21st edn, Vol. 1 (eds Helmchen, G. et al.) 75-146 (Thieme, Stuttgart, 1996)

3. Comprehensive Asymmetric Catalysis Vols I-III (eds Jacobsen, E. N., Pfaltz, A. & Yamamoto, H.) (Springer, Heidelberg, 1999)

4. Thayer, A. M. Chem. Eng. News 84(33), 15-31 (2006)

5. Ohno, M. & Otsuka, M. Org. React. 37, 1-55 (1989)

Nature http://www.nature.com/nature

ScienceWeek http://scienceweek.com

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