Complexity Digest 2000.36

04-Sep-2000

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Content

  1. When Did Photosynthesis Emerge on Earth?, Science
  2. What Factors Drive Climate Change?, PNAS/Nature/Science
  3. Climate Change And Health, Science
  4. Global Environmental Collaborations, Science/WorldLink
  5. Origin Of Complexity In Multicellular Organisms, arXiv
  6. How Well Can An Amoeba Climb?, PNAS
  7. Darwin Goes Digital, WorldLink
  8. Possible Cause For Debilitating Sleep Disorder Narcolepsy, Science Daily
  9. Genetically Modified Crops and Farmland Biodiversity, Science
  10. Hypnosis Found To Alter The Brain, Harvard U. Gazette
  11. Links &amp Snippets
    1. 1 Good Memories Of Bad Events In Infancy, Nature
    2. 6 Us Grant Glues 'Virtual Cell' Together, Nature
    3. 5 Applications of Swarm Models, Swarm.org
    4. 2 Bouncing C60 Buckyball Transistors, Nature
    5. 3 Invariants, Scaling Laws, and Ecological Complexity, Science
    6. 4 Switching From Simple To Complex Oscillations In Calcium Signaling, Biophys. J

  1. When Did Photosynthesis Emerge on Earth?, Science Next Article Bookmark and Share

    One of the most dramatic "innovations" on our planet happened more than three billion years ago: The conversion of sunlight into biologically useful energy. "When our biosphere developed photosynthesis, it developed an energy resource orders of magnitude larger than that available from oxidation-reduction reactions associated with weathering and hydrothermal activity. (…) the onset of oxygenic photosynthesis most probably increased global organic productivity by at least two to three orders of magnitude."

    Whereas "modern" forms of photosynthesis occurs together with the release of free oxygen into the atmosphere, Xiong et al provide evidence that the first forms of photosynthesis were not coupled to the production of oxygen: "The authors demonstrate conclusively for the first time that the major lineages of pigments involved in anoxygenic photosynthesis arose before the development of oxygenic photosynthesis."

    One reason could be that during the first billion years after the formation of earth strong geothermal activity combined with "vigorous geothermal outgassing" supported life forms that utilized sunlight but did not generate oxygen. Xiong et al. come to the conclusion: "that chlorophyll a biosynthesis evolved from a more complex bacteriochlorophyll biosynthesis pathway argues against the oft-cited Granick hypothesis for the evolution of chlorophylls. Granick proposed that chlorophyll a, which requires fewer biosynthetic steps in its production, evolved before bacteriochlorophylls. The molecular phylogeny for the bch/chl genes in this, and in other studie), strongly argues that cyanobacteria were late-evolving.


  2. What Factors Drive Climate Change?, PNAS/Nature/Science Next Article Bookmark and Share

    The complexity of the terrestrial climate system is far from being completely understood by today's science. Just as the role of carbon dioxide (CO2) as green house gas (GHG) finds global acceptance new scientific results demonstrate how much more complex the whole story is. Hansen et al. state: "(…) we argue that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases (GHGs), such as chlorofluorocarbons, CH4, and N2O, not by the products of fossil fuel burning, CO2 and aerosols, the positive and negative climate forcings of which are partially offsetting. (…)We argue that black carbon aerosols, by means of several effects, contribute significantly to global warming."

    Especially the role of aerosols seems to be of critical importance because of their role in cloud formation. Schrope observes: "Tiny airborne particles affect the Earth's climate, in part by influencing the formation of clouds. But modeling the effects of these aerosols is proving to be one of the thorniest problems in climatology (…). One of the main complicating factors in modeling the effect of aerosols is their short residence times in the atmosphere. Typically, particles remain aloft for a week or less(…). In contrast, molecules of carbon dioxide persist for about a century, and other greenhouse gases also have long residence times."

    Hansen et al also mention the possibility of stripping black carbon emissions at fossil fuel power plants.which could have a big impact since electricity plays an increasing role in future energy systems. They also mention that "Stripping and disposal of CO2, although more challenging, provide an effective backup strategy." Related to this point is an article by Abelson who writes: "Worldwide emissions of CO2 continue to increase, and prudence dictates that technologies be developed to help limit this trend. One of several ways to attenuate the increase of CO2 in the atmosphere is to sequester it. The technology for doing so exists. The injection of CO2 into oil fields is having economically beneficial effects while at the same time sequestering CO2."


  3. Climate Change And Health, Science Next Article Bookmark and Share

    We know from complex systems that changes in one subsystem generally will effect the dynamics of other subsystems. Two papers study the coupling between climate and health:

    Rogers et al. write: "The frequent warnings that global climate change will allow falciparum malaria to spread into northern latitudes, including Europe and large parts of the United States, are based on biological transmission models driven principally by temperature. (…) In an alternative statistical approach, the recorded present-day global distribution of falciparum malaria was used to establish the current multivariate climatic constraints. These results were applied to future climate scenarios to predict future distributions, which showed remarkably few changes, even under the most extreme scenarios."

    A more current problem is described by Pascual et al.: "Analysis of a monthly 18-year cholera time series from Bangladesh shows that the temporal variability of cholera exhibits an interannual component at the dominant frequency of El Niño-Southern Oscillation (ENSO). Results from nonlinear time series analysis support a role for both ENSO and previous disease levels in the dynamics of cholera. Cholera patterns are linked to the previously described changes in the atmospheric circulation of south Asia and, consistent with these changes, to regional temperature anomalies."


  4. Global Environmental Collaborations, Science/WorldLink Next Article Bookmark and Share

    The complexity of the global environmental system increasingly requires projects that are global and interdisciplinary in nature. A new collaborative project is to assess critical ecosystems around the world: The "Millennium Ecosystem Assessment" ), a 4-year, $20 million effort that will get under way early next year.

    The assessment will turn loose ecologists and social scientists to gather and analyze data on the state of the world's ecosystems, assess nature's ability to provide essential "services" such as food and clean water, and project environmental trends such as deforestation, loss of species, and pollution "

    "French prime minister Lionel Jospin recently urged establishing a Global Environmental Organisation (GEO). Describing the current international governance "architecture" as deficient, Jospin argued for a restructuring and strengthening of the global-scale capacity to control pollution and manage shared natural resources.(…)

    An effective GEO need not be a big, new bureaucracy. To the contrary, a streamlined agency that consolidates many of the entities identified above, supported by a decentralized (largely virtual) structure of outside experts (national government officials, academics, business and NGO leaders) would make more sense. With a "global policy network" as its core and a modern organizational design that takes advantage of the technologies of the information age, such a GEO could move quickly on breaking issues, bring analytical rigor to hard problems and be entrepreneurial in the development of response strategies - all with much lower overhead than traditional international organizations.

    In revitalizing global environmental governance, focus must be the watchword. UNEP has got bogged down carrying out projects in dozens of countries. While independently worthy, these local-issue-oriented activities should be undertaken by national governments supported by UNDP or the World Bank. "


  5. Origin Of Complexity In Multicellular Organisms, arXiv Next Article Bookmark and Share

    Abstract: #Through extensive studies of dynamical system modeling cellular growth and reproduction, we found evidence that complexity arises in multicellular organisms naturally through evolution. Without any elaborate control mechanism, these systems can exhibit complex pattern formation with spontaneous cell differentiation. Such systems employ a `cooperative' use of resources and maintain a larger growth speed than simple cell systems, which exist in a homogeneous state and behave 'selfishly'. The relevance of the diversity of chemicals and reaction dynamics to the growth of a multicellular organism is demonstrated. Chaotic biochemical dynamics are found to provide the multi-potency of stem cells.

    Excerpt:" Multicellular organisms consist of differentiated cell types, with rather complex biochemical dynamics exhibited by complex metabolic and genetic networks. Through the course of development, cells differentiate into several types and often form complex patterns. The molecular mechanisms existing of each stage of development have been elucidated experimentally. However, it is still not clear why multicellular organisms should have such complexity, nor why such inhomogeneities in cell types and patterns are common. These are not trivial problems, since a simple biochemical network would be sufficient (and perhaps more fit) to produce identical cells rapidly and faithfully. Here we give an answer to the problem of why multicellular organisms in general have diverse cell types with complex patterns and dynamics."


  6. How Well Can An Amoeba Climb?, PNAS Next Article Bookmark and Share

    As the technological frontier moves towards nano scales it is important to understand not only information related processes but also how movement takes place at very small scales. Fukui et al studied the forces involved in the movement of some of the smallest moving creatures, Amoeba:

    Abstract: "We report here our efforts to measure the crawling force generated by cells undergoing amoeboid locomotion. In a centrifuge microscope, acceleration was increased until amoebae of Dictyostelium discoideum were "stalled" or no longer able to "climb up." The "apparent weight" of the amoebae at stalling rpm in myosin mutants depended on the presence of myosin II (but not myosins IA and IB) and paralleled the cortical strength of the cells. Surprisingly, however, the cell stalled not only in low-density media as expected but also in media with densities greater than the cell density where the buoyant force should push the amoeba upward. We find that the leading pseudopod is bent under centrifugal force in all stalled amoebae, suggesting that this pseudopod is very dense indeed. This finding also suggests that directional cell locomotion against resistive forces requires a turgid forward-pointing pseudopod, most likely sustained by cortical actomyosin II. "

    • How Well Can An Amoeba Climb?, Yoshio Fukui, Taro Q. P. Uyeda, Chikako Kitayama, and Shinya Inoué, Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 18, 10020-10025, August 29, 2000

  7. Darwin Goes Digital, WorldLink Next Article Bookmark and Share

    "As management mantras, they have become over-worked cliches: "Only the fittest survive" intones the CEO; "Adapt or die" declares the management consultant. In these dog-eat-dog times, it is fashionable to invoke the language of Charles Darwin.

    But these same mantras are now being taken quite literally by scientists who have made them the core of a powerful new technique for solving problems of stunning complexity.

    New, that is, for humans. Nature has been using it to impressive effect for aeons. Biologists call it evolution, and now computer scientists have re-invented it, and given it a new name: genetic programming. And it's starting to show its mettle in a host of fields, from electronics to car design to code-breaking.

    Despite its imposing moniker, the idea behind "GP" could hardly be simpler. Through the process of evolution, nature has succeeded in finding a whole host of answers to a tough problem - survival. From ants to zebras, pond-life to predators, every living creature is a "solution" to the survival problem, each found after countless millennia of breeding and natural selection: the survival of the fittest.

    Around 40 years ago, American computer scientist John Holland wondered if the same process could be used to tackle rather more prosaic problems - the best-possible openings in chess, for example. His idea was to start with a random set of guesses to the answer, test each of them and kill off all but the best guesses in a bout of Darwinian survival of the fittest. These would then be combined in a form of computerised sex, mixing different bits of each guess to "breed" a new - and hopefully better - set. Repeat that evolutionary process a few times, thought Holland, and perhaps a truly fit solution would emerge."


  8. Possible Cause For Debilitating Sleep Disorder Narcolepsy, Science Daily Next Article Bookmark and Share

    Excerpt: "Scientists believe they may have identified the cause of the debilitating sleep disorder narcolepsy in humans. A new study shows a dramatic reduction - up to 95 percent - in the number of neurons containing a substance called hypocretins in the brains of people with narcolepsy compared to control brains. Hypocretin peptides are neurotransmitters that play an important role in regulating sleep and appetite. The researchers hypothesize that the pronounced loss of these neurons could be caused either by a neurodegenerative process or an autoimmune response.

    Narcolepsy is a disabling sleep disorder that affects 135,000 Americans. Patients suffer from excessive daytime sleepiness; sudden brief episodes of muscle weakness or paralysis, also called cataplexy; paralysis while sleeping or upon waking up; and vivid dream-like images that occur at sleep onset. The disorder is often difficult to diagnose, and there is presently no cure.

    The study, led by Jerome M. Siegel, Ph.D., Professor of Psychiatry and Biobehavioral Sciences at the University of California at Los Angeles, and Chief of Neurobiology Research at the Veterans Administration in Sepulveda, is being published in the September 2000 issue of Neuron. Dr. Siegel's work is supported in part by the National Institute of Neurological Disorders and Stroke (NINDS).

    Recent studies have shown that there is a genetic component to narcolepsy in dogs and mice involving mutations of the hypocretin precursor or receptor genes. However the authors point out that the genetics of human narcolepsy are well defined - most narcoleptics generally do not have first degree relatives with the disorder. When present in identical twins, in most cases only one twin is affected. "


  9. Genetically Modified Crops and Farmland Biodiversity, Science Next Article Bookmark and Share

    Part of the debate surrounding genetically modified (GM) crops concerns the possibility of unanticipated environmental effects. Watkinson et al. (see the Perspective by Firbank and Forcella) present a model analysis of the potential impact of herbicide-tolerant crops on weed and bird populations. Their analysis consists of the linkage between a dynamic model of weed population at the field scale that includes parameters for crop management, a frequency distribution of weed levels across fields, and a model of the response of a bird species to these frequency distributions.

    The simulation of herbicide application results in severe reduction of weed populations that eventually affects the populations of seed-eating birds.


  10. Hypnosis Found To Alter The Brain, Harvard U. Gazette Next Article Bookmark and Share

    Excerpts: People have been hypnotized to see color where only shades of gray exist, and to see gray when actually looking at brightly colored rectangles.

    That result wouldn't be so surprising at a carnival or stage show, but it comes from a tightly controlled scientific experiment done at a Harvard University medical facility.

    Researchers separately hypnotized eight people as they lay in a scanning machine that recorded activity in their brains. These subjects then tried to drain bright color from pictures, or see color where none existed. They also attempted to do the same thing when not hypnotized. The records of cerebral activity clearly show that hypnosis can change the state of the brain.

    "Hypnosis has a contentious history," notes Stephen Kosslyn, professor of psychology at Harvard and leader of the study. "Some insist it's a state of mind that differs from normal states and involves unique consequences; others say it's nothing more than state-show gimmickry." (...)

    When not under hypnosis, people asked to perceive color – whether they actually saw color or not – showed activity on only the right side of their brains. (The brain is split into right and left hemispheres by a furrow filled with nerve fibers that connect the two halves.) When told to see gray, whether looking at color or gray, again changes in activity occurred on the right side only.

    That result was expected on the basis of previous research. However, under hypnotism the researchers found what Kosslyn calls "a curious tweak." Both the left and right hemispheres responded. In other words, the right side of the brain alone responded to what the subjects saw when they were not hypnotized, but both sides responded under hypnosis.

    "The left hemisphere color area registered what people were told to see only when they were hypnotized. The right hemisphere registered what people were told to see [independently of what they actually saw] whether or not they were hypnotized," Kosslyn explains. "If you ask people [who are not hypnotized] to visualize color in a gray pattern, or vice versa, only the right hemisphere is activated during the task. Thus, our findings in the left hemisphere could not have been produced by mental imagery alone.

    "What we have shown for the first time," Kosslyn concludes, "is that hypnosis changes conscious experience in a way not possible when we are not under hypnosis."


  11. Links &amp Snippets Next Article Bookmark and Share

    1. 1 Good Memories Of Bad Events In Infancy, Nature Next Article Bookmark and Share

      If a helpless newborn infant does not form an attachment to its care-giver, even an abusive one, its chances of survival diminish (…). As a part of the brain called the amygdala is critical for learned fear in adult animals, we investigated whether the development of learned avoidance behavior could be delayed by late maturation of amygdala function. We found that very young rat pups exposed to various odors associated with shock treatment learn an approach response to that odor, whereas older pups learn odor avoidance. We show that the origin and development of learned odor-avoidance behavior is associated with enhanced neural responses in the amygdala during odor-shock conditioning.


    2. 6 Us Grant Glues 'Virtual Cell' Together, Nature Next Article Bookmark and Share

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      The US National Institutes of Health (NIH) this week launched a new series of grants for large-scale collaborative projects by pledging $25 million over five years towards the construction of a 'virtual cell'.

      The first ever 'glue grant' - so-called because it aims to link research between different institutions - has been awarded to the Alliance for Cellular Signaling (AFCS), a consortium based at the University of Texas Southwestern Medical Center and headed by Al Gilman, professor of pharmacology there.


    3. 5 Applications of Swarm Models, Swarm.org Next Article Bookmark and Share

      Swarm has been developed as one of the first simulation environments for complex adaptive systems. While it started up as an academic research tool it now has found quite a number of applications in areas like biology, ecology, culture/anthropology, computer science/industry, economics, Political Science, geography, and defense related simulations.

      One example of particular interest in relation to the recent spread of forest fires is Arborgames: "Arborgames is a model of forest dynamics whose goal is to examine the role of fire on species diversity. It is a member of a long lineage of individual-based, spatially explicit models of forests which assume discrete cells with one individual per cell. The local interaction of trees in a neighborhood, however, allow Arborgames to generate landscape dynamics that respond to disturbance in a recursive way. The behavior of fire is governed by the contagion of local forest structure, which in turn is governed by the pattern of past fires."


    4. 2 Bouncing C60 Buckyball Transistors, Nature Next Article Bookmark and Share

      "Park et al. have created a three-electrode transistor from a single C60 molecule. "In fact, this is the smallest field-effect transistor ever built. The small size of C60 allows only one electron at a time to hop, or tunnel, on and off the molecule. This means that the device is a so-called single-electron transistor. Second, the single- electron current can both excite and detect the mechanical oscillations of the C60 ball. To understand this electro-mechanical coupling we need to consider the energies that are involved in the different tunnelling processes."


    5. 3 Invariants, Scaling Laws, and Ecological Complexity, Science Next Article Bookmark and Share

      The inverse relation between body size and population density in animal species is well established but only rarely has it been quantified accurately. Schmid et al. now provide a survey, unrivaled in its detail, of body size and population density of several hundred species of invertebrates in two geographically separate European stream communities. Both communities, while sharing only a small proportion of species, have acquired similar density-size relations. They argue that the similarity of the distributions is brought about by the similarities in the physical properties of the two stream systems.


    6. 4 Switching From Simple To Complex Oscillations In Calcium Signaling, Biophys. J Bookmark and Share

      Abstract: We present a new model for calcium oscillations based on experiments in hepatocytes. The model considers feedback inhibition on the initial agonist receptor complex by calcium and activated phospholipase C, as well as receptor type-dependent self-enhanced behavior of the activated G subunit. It is able to show simple periodic oscillations and periodic bursting, and it is the first model to display chaotic bursting in response to agonist stimulations. Moreover, our model offers a possible explanation for the differences in dynamic behavior observed in response to different agonists in hepatocytes.


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