Complexity Digest 2000.15

10-Apr-2000

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Content

  1. The Way Things Move, Science
  2. Intermittent Movement in Animals, Science
  3. Learning How Our Body Interacts With The World, BBS
  4. Intentionality Detection And "Mindreading", PNAS
  5. Spatial Memory of Taxi Drivers, PNAS
  6. Zebra Fish With Two Clocks, PNAS
  7. Intimations of Immortality, Science
  8. Remote Control: Telecommuting, Business Week
  9. 1,800-Year Tidal Cycle And Rapid Climate Change, PNAS
  10. Cheating Bacteria, Nature
  11. 'The Climate Symphony' Performance, Announcement
  12. Links & Snippets
    1. Robots That Imitate Life, Science
    2. Iridium Global Satellite System Terminated, Responses

  1. The Way Things Move, Science Next Article Bookmark and Share

    While scientists are working hard to build a nano-scale motor on a chip nature has evolved a whole ensemble of protein-based nano-scale motors that fall into only two main categories: microtubule-based kinesin motors and actin-based myosin motors. They are not only responsible for basically all locomotion of animals but they also generate intracellular traffic, divide and move cells, transport membranes, and generate many other forms of movement that are characteristic for living systems.

    It is interesting that just like the original and still prevalent type of internal combustion engines, protein motors generate motion by moving a tiny piston (filament) within a nano polymer track (cylinder). The basic displacement unit ("nano twitch") is about 10 nm, about ten million times smaller than the piston movement in your car.

    The two different types of protein movement are distinguished by the way they move along the filament: They either use a lever that swings back and forth or they move processively along a track (see animations at : http://www.fivth.com).

    Both motor types use the same fuel ATP that is burned to ADP that means that the presence or absence of a single phosphate group will change the conformational state of the protein and induce movement. Once this basic motor unit was available to biological systems, evolutionary processes selectively produced the tremendous diversity of movements classes that we can observe today. There is some impressive evidence that those movement types are indeed universal: Karl Simms built artificial creatures in silico in the form of linked blocks ("blockies") and allowed them to evolve in different environments. The typical types of movement such as crawling and hopping did indeed emerge together with a number of less biological movement classes. (See video at: Karl Sims' Evolving Virtual Creatures )


  2. Intermittent Movement in Animals, Science Next Article Bookmark and Share

    In long-distance ( > 50 miles) horse-back racing we spent a lot of time training the horses to travel at an even-paced, fast trot. Now, the report by Pennisi seems to suggest that we might have been better off with a gallop + walk strategy.

    It seems that a wide class of animals has selected to move intermittently and there appears to be physiological reasons why that type of movement has an evolutionary advantage over keeping a uniform pace. Whales and dolphins can use their oxygen much more efficiently with a combination of swimming and sinking movements, utilizing their change in buoyancy due to their compressed lungs at different depths.

    Many small animals developed the same strategy for different reasons: During the rest period they are better able to spot predators and quick sprints at unpredictable times make it harder for those predators to catch them that went undetected.

    For humans a more intermittent type of movement might be beneficial because of the bio-chemical processes in the muscles. The enzyme pyruvate dehydrogenase seems to play a special role in this process: it is "converting the pyruvate into acetyl molecules (acetyl-CoA), which in turn are put to use by mitochondria, the cell's power plant, to produce ATP, the energy currency of the cell." (…). "Extra pyruvate is shunted into another pathway that creates lactic acid. If ATP is not produced fast enough, the muscle turns to another energy source, phosphocreatine, a last-ditch source of energy. But when the phosphates that are a byproduct of this fuel build up, they and the accumulated lactic acid cause the muscle fatigue familiar to every athlete."

    It could be shown that intermittent movement reduces the chance of producing lactic acid and thereby allows the muscles to work more efficiently.


  3. Learning How Our Body Interacts With The World, BBS Next Article Bookmark and Share

    Abstract: The overall goal of this target article is to demonstrate a mechanism for an embodied cognition. The particular vehicle is a much-studied, but still widely debated phenomenon seen in 7-12 month-old-infants. In Piaget's classic "A-not-B error," infants who have successfully uncovered a toy at location "A" continue to reach to that location even after they watch the toy hidden in a nearby location "B."

    Here we question the traditional explanations of the error as indicator of infants' concepts of objects or other static mental structures. Instead, we demonstrate that the A-not-B error and its previously puzzling contextual variations can be understood by the coupled dynamics of the ordinary processes of goal-directed actions: looking, planning, reaching, and remembering. We offer a formal dynamic theory and model based on cognitive embodiment that both simulates the known A-not-B effects and offers novel predictions that match new experimental results.

    The demonstration supports an embodied view by casting the mental events involved in perception, planning, deciding and remembering in the same analogic dynamic language as that used to describe bodily movement, so that they may be continuously meshed. We maintain that this mesh is a pre-eminently cognitive act of "knowing" not only in infancy but also in everyday activities throughout the life span.


  4. Intentionality Detection And "Mindreading", PNAS Next Article Bookmark and Share

    Abstract: By around the age of 4 years, children "can work out what people might know, think or believe" based on what they say or do. This is called "mindreading," which builds upon the human ability to infer the intentions of others. Game theory makes a strong assumption about what individual A can expect about B's intentions and vice versa, viz. that each is a self-interested opponent of the other and will reliably analyze games by using such basic principles as dominance and backward induction, and behave as if the normal form of an extensive form game is equivalent to the latter. But the extensive form allows intentions to be detected from actual sequential play and is therefore not necessarily equivalent psychologically to the normal form.

    We discuss Baron-Cohen's theory of the mindreading system [Baron-Cohen, S. (1995) Mindblindness: An Essay on Autism and Theory of Mind (MIT Press, Cambridge, MA)] to motivate the comparison of behavior in an extensive form game with its corresponding normal form. As in the work of Rapoport [Rapoport, A. (1997) Int. J. Game Theory 26, 113-136] and Schotter et al. [Schotter, A., Wiegelt, K. & Wilson, C. (1994) Games Econ. Behav. 6, 445-468], we find consistent differences in behavior between the normal and extensive forms. In particular, we observe attempts to cooperate, and in some treatments we observe the achievement of cooperation, occurring more frequently in the extensive form. Cooperation in this context requires reciprocity, which is more difficult to achieve by means of intentionality detection in the normal as opposed to the extensive form games we study.


  5. Spatial Memory of Taxi Drivers, PNAS Next Article Bookmark and Share

    Abstract: Structural MRIs of the brains of humans with extensive navigation experience, licensed London taxi drivers, were analyzed and compared with those of control subjects who did not drive taxis. The posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects. A more anterior hippocampal region was larger in control subjects than in taxi drivers. Hippocampal volume correlated with the amount of time spent as a taxi driver (positively in the posterior and negatively in the anterior hippocampus).

    These data are in accordance with the idea that the posterior hippocampus stores a spatial representation of the environment and can expand regionally to accommodate elaboration of this representation in people with a high dependence on navigational skills. It seems that there is a capacity for local plastic change in the structure of the healthy adult human brain in response to environmental demands.


  6. Zebra Fish With Two Clocks, PNAS Next Article Bookmark and Share

    Abstract: Most clock genes encode transcription factors that interact to elicit cooperative control of clock function. Using a two-hybrid system approach, we have isolated two different partners of zebrafish (zf) CLOCK, which are similar to the mammalian BMAL1 (brain and muscle arylhydrocarbon receptor nuclear translocator-like protein 1). The two homologs, zfBMAL1 and zfBMAL2, contain conserved basic helix-loop-helix-PAS (Period-Arylhydrocarbon receptor-Singleminded) domains but diverge in the carboxyl termini, thus bearing different transcriptional activation potential. As for zfClock, the expression of both zfBmals oscillates in most tissues in the animal. However, in many tissues, the peak, levels, and kinetics of expression are different between the two genes and for the same gene from tissue to tissue.

    These results support the existence of independent peripheral oscillators and suggest that zfBMAL1 and zfBMAL2 may exert distinct circadian functions, interacting differentially with zfCLOCK at various times in different tissues. Our findings also indicate that multiple controls may be exerted by the central clock and/or that peripheral oscillators can differentially interpret central clock signals.


  7. Intimations of Immortality, Science Next Article Bookmark and Share

    Societies as complex adaptive systems will eventually learn from their mistakes and improve planning for instance by more reliable forecasting about the consequences of innovations especially in the scientific and technological domain. It is safer to think and plan how to deal with an atomic bomb instead of having it first delivered and then develop ad-hoc strategies how to use (or not-use it).

    For some reason it seems that ethics professors have acquired the role of thinking about consequences of technological progress for society. Maybe that is good so because often their scenarios are more like science fiction in that they repeat ancient essays on human responsibility and conflict. On the other hand on might wonder why so few ethics professors play an active role in politics.

    Harris has been thinking about the consequences of people living longer or even become immortal. I couldn't help getting the impression that he treated this problem as some sort of puzzle or game for which he was asked to invent the rules. One of the players is "society" others are privileged/rich or under privileged/poor people.

    Some of the rules he came up with are: "society offers you a live pro-longing therapy if you promise not to reproduce as long as you live plus forfeit the right to subsequent therapies." Or how about a rule of "generational cleansing"? Why does this sound so much like British high school debating club?

    Nothing in his analysis mentions market driven solutions. He doesn't discuss the approach by the health insurance industry that determines how much money they are willing or able to spend on life-prolonging therapies.

    But his essay brings up the question about what to do about over-population. That is a real problem today even without a life expectancy of over 120.


  8. Remote Control: Telecommuting, Business Week Next Article Bookmark and Share

    One of the fundamental shifts that our societies are undergoing during the transition from the industrial to the information age is that information work can be done everywhere where there is access to the Internet. And that is already basically any place on this planet even after the Iridium LEO satellites will be burned-up in the atmosphere.

    A logical consequence is that information worker won't have to go to an information factory clogging the roads on their way to work.

    Today already more than 2.2 million employees or 28.9% of small US companies (less than one hundred employees) telecommute at least three days per month. Especially employees with children have benefits from this option but the option to work at home seems to improve motivation. For managers one of the central problems is to make sure that teams will continue to work efficiently without daily face-to-face interactions. From the accumulated experience a number of rules seem to emerge: The team-members need to be in communication. E-mail and other electronic communication tools only work if they are used and timely responses to messages are reliably received. Some companies give their employees cell phones with the understanding that they need to answer it during business hours within "two rings".

    Another shift seems to be essential in this transition: information workers at home usually don't work with time clocks. Therefore result based salaries instead of hourly wages appear to be more appropriate.


  9. 1,800-Year Tidal Cycle And Rapid Climate Change, PNAS Next Article Bookmark and Share

    Abstract: Variations in solar irradiance are widely believed to explain climatic change on 20,000- to 100,000-year time-scales in accordance with the Milankovitch theory of the ice ages, but there is no conclusive evidence that variable irradiance can be the cause of abrupt fluctuations in climate on time-scales as short as 1,000 years. We propose that such abrupt millennial changes, seen in ice and sedimentary core records, were produced in part by well characterized, almost periodic variations in the strength of the global oceanic tide-raising forces caused by resonances in the periodic motions of the earth and moon.

    A well defined 1,800-year tidal cycle is associated with gradually shifting lunar declination from one episode of maximum tidal forcing on the centennial time-scale to the next. An amplitude modulation of this cycle occurs with an average period of about 5,000 years, associated with gradually shifting separation-intervals between perihelion and syzygy at maxima of the 1,800-year cycle. We propose that strong tidal forcing causes cooling at the sea surface by increasing vertical mixing in the oceans. On the millennial time-scale, this tidal hypothesis is supported by findings, from sedimentary records of ice-rafting debris, that ocean waters cooled close to the times predicted for strong tidal forcing.

  10. Cheating Bacteria, Nature Next Article Bookmark and Share

    Cheating seems to be a universal property of complex adaptive systems: As soon as collective behavior and self-organization of subsystem takes place, some of the subsystems take advantage of the super-structure and thereby gain evolutionary advantage. This parasitic behavior only can be sustained as long as the fraction of cheaters is small. The bacterium Myxococcus xanthus -a prokaryote- exhibits several social behaviours, including aggregation of cells into spore-producing fruiting bodies during starvation. This is quite similar to the behavior of one of the standard examples of biological self-organization the eukaryotic slime mould Dictyostelium discoideum.

    It is known that both creatures (or some cells of it) cheat in the sense that they develop mutant cells that sporulate much more efficiently than wild type at low initial frequencies.

    "Two features of the myxobacteria suggest they do not exclude cheaters by single-spore dispersal. First, M. xanthus spores adhere tightly to one another and require vigorous sonication to separate them in the laboratory. Thus, new colonies in nature are probably founded by multiple clumped spores. Second, myxobacteria are highly motile, promoting migration that opposes the homogenizing effect of single-spore colonization. Barring some unknown policing mechanism that represses cheater genotypes, we therefore predict that cheaters are common in natural populations of M. xanthus ."


  11. 'The Climate Symphony' Performance, Announcement Next Article Bookmark and Share

    Durham, NH Scientists at the Climate Change Research Center at the University of New Hampshire and computer scientist and musician Marty Quinn of Design Rhythmics Sonification Research Lab have collaborated to create a uniquely entertaining and enlightening live concert of 110,000 years of earths climate history. On April 21 at the American Museum of Natural History in NY, Marty Quinn will perform his original "Climate Symphony", along with discussion from mathematician and professor Dr. Dave Meeker. Dr. Meeker is responsible for the analysis of the 'forcing frequencies of nature' found in the ice core data and from which the music is generated. The ice sheet movements down and up over the earths surface and the volcanic data will be performed live on specially made ice core drums by Marty, while the rest of the data music will be triggered from the drum playing. Other climate elements include the elliptical orbit of the earth, the intensity of the sun, the ocean circulation, the precessions and the wobble of the earths axis. A simulated ice core extraction room sets the stage.

    The data for this event was gathered between 1989 and 1993 by the US Greenland Ice Sheet Project 2 (GISP2) and the European Greenland Ice Core Program (GRIP). The music was featured last year at the American Museum of Natural History in a talk by Dr. Paul Mayewski, Director of the Climate Change Research Center and GISP2-Science Management Office, on rapid climate change events detected in the research. Mayewski, Quinn and Meeker have been working over the past three years to create a musical analog so that the public would have another way to experience these research results through the powerful and familiar mechanism of music. The concert performance will be available to tour schools and museums throughout the country.

    Marty Quinn is a professional musician and computer scientist. He founded the Design Rhythmics Sonification Research Lab in 1992 for the purpose of representing data in highly musical forms. His work includes musical, rhythmic and geometric representations of data including ice core, El Níno, DNA, seismic and textual data. He is currently exploring the transformation of radar data into music and intelligent alarms for the US International Trans-Antarctic Scientific Expedition (ITASE) project.

    Since 1991, Dr. Loren David Meeker PhD has been a research mathematician at the Climate Change Research Center at the University of New Hampshire's Institute for the Study of Earth, Oceans, and Space in its effort to determine, describe and understand the mechanisms of natural climate change from the records of atmospheric chemistry deposited in glaciers around the world. He has published over 80 papers.


  12. Links & Snippets Next Article Bookmark and Share


    1. Robots That Imitate Life, Science Next Article Bookmark and Share

      Excerpt: "Robot-building collaborations are often sprawling and involve unlikely partners: computer scientists, mathematicians, electrical and mechanical engineers, as well as biologists and zoologists. At Case Western, for instance, the program started with Randall Beer, a computer scientist who was frustrated by the slow progress in artificial intelligence and thought guidance might be found in the nervous systems of simple insects. Beer began collaborating with Case Western biologists Roy Ritzman and Hillel Chiel, and created a computer simulation of a walking insect. "

    2. Iridium Global Satellite System Terminated, Responses Bookmark and Share

      Excerpts from an e-mail discussion about ways to rescue the Iridium satellites (see ComDig 2000.10.9)

      (...)

      (5) The key is if the satellite can be used for narrow-band (and preferably for broadband) Internet -- e.g., for our Global University System with global broadband Internet -- see; <http://www.friends-partners.org/GLOSAS/Global_University/Global%20University%20System/Synopsis_11-5-99.html>, and also; <http://www.friends-partners.org/GLOSAS/Tampere_Conference/Global_Broadband_Internet/Global_Broadband_Internet.html>

      (6) Your Warn and Recovery Net (WARN)" system has already been using a couple of LEO satellites for humanitarian purposes - <http://www.informatics.org/clarke/projects.html>.

      (…)

      (9) If this will succeed, the satellites could be a part of our proposed Global Service Trust Fund (GSTF) -- see; <http://www.informatics.org/clarke/projects.html>, and <http://www.friends-partners.org/GLOSAS/Tampere_Conference/GSTF/Synopsis_2-15-00.html>.


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