Editors' Choice

Science  23 Oct 2009:
Vol. 326, Issue 5952, pp. 503
  1. Evolution

    Not So Useless

    1. Caroline Ash

    For humans, the value of having an appendix seems to be negligible and, given the prevalence of appendicitis, having an appendix can even be dangerous. This gut attachment has long been thought to be a remnant of the time when hominids ate a high proportion of plant matter that needed fermentation before digestion. More recently, the appendix has been proposed to play a role in the immune-mediated maintenance of symbiotic bacteria in the gut. On the basis of comparative anatomical and phylogenetic approaches, Smith et al. now contend that the appendix is a specialized organ for harboring symbiotic bacteria essential for health. Diarrhea was a common hazard during hominid evolution. Because the opening to the appendix is constricted, it may escape colonization by bacterial pathogens. Bacterial symbiont reconstitution after diarrhea can be achieved rapidly from the populations harbored in the appendix. Thus, far from being useless, positive selection may well have acted to maintain the appendix.

    J. Evol. Biol. 22, 1984 (2009).

  2. Physics

    A Cloudy Thermometer

    1. Jelena Stajic

    Some of the coldest places on our planet are created in physics laboratories, where dilute alkali gases are coaxed into showing their quantum character. To prepare the samples, experimenters employ irreversible methods such as evaporative and sympathetic cooling. It is often hard to measure the final temperature of the gases, however, particularly in contexts where they are loaded into optical lattices to simulate condensed-matter systems such as Mott insulators and superconductors. Catani et al. address this challenge by tracking entropy, rather than temperature (which, technically speaking, is a measure of how much a system's entropy changes on incremental energy input). Specifically, they load two distinguishable Bose gases into the same magnetic trap and then apply an additional optical trap that affects only one of them, the target gas. By slowly increasing the strength of the trap, they achieve an exact entropy transfer from the target gas (41K) to the auxiliary gas (87Rb), condensing the K and maintaining the temperature equilibrium between the two gases. Through cycles of compression and decompression, they observe oscillation of the K ensemble between condensed and uncondensed states. When the target gas is then loaded into a one-dimensional optical lattice, its temperature is directly reflected in the auxiliary gas cloud size after expansion.

    Phys. Rev. Lett. 103, 140401 (2009).

  3. Neuroscience

    Memories of MAP Kinase Activation

    1. L. Bryan Ray

    We all know from experience that nothing beats repetition to help us store memories. New studies in the fruit fly of a gene associated with Noonan syndrome, which in humans causes abnormal development and learning disabilities, have implicated a role for signaling through the mitogen-activated protein kinase (MAPK) pathway in the consolidation of long-term memories in the brain. Mutations that cause Noonan syndrome are clustered in components of the MAPK signaling pathway, in particular, the gene encoding the protein tyrosine phosphatase PTPN11. Pagani et al. characterized the effects of the Drosophila ortholog of PTPN11, called corkscrew (CSW), that promotes MAPK signaling. In a learning task in which repetition of exposure to a stimulus was required to produce long-term memory and in which the time between training events was also critical, genetic or pharmacological inhibition of CSW specifically inhibited long-term memory formation. Overexpression of CSW in brain neurons altered the intervals required between trials. Successful generation of long-term memories was correlated with conditions that allowed a transient peak in MAPK activity after each training trial. Thus, waves of MAPK signaling may be part of the molecular mechanism through which properly spaced repetitions of a task produce long-term memories.

    Cell 139, 186 (2009).

  4. Climate Science

    Dates in a Cave

    1. H. Jesse Smith

    Stalagmites—one type of a class of secondary mineral deposits, or speleothems, formed in caves—can provide precisely datable records of climate if they formed under the right conditions. Their datability is in fact almost unparalleled in most paleoclimate proxies. Fleitmann et al. present a record of climate, derived from stalagmites found in northern Turkey, which covers the past 50,000 years, including the 13 most recent Greenland interstadial (cold) events. The record closely resembles the Greenland ice core record of these episodes. The stalagmites can be dated much more precisely than the ice cores, however, and thus should generate a better ice chronology than those that exist now. Moreover, the improved age scale for the Greenland interstadial events does not support the idea (based on age models derived from ice cores) that the events occurred with an irregular periodicity of 1500 years, suggesting instead that the events were more likely to be stochastic in origin.

    Geophys. Res. Lett. 36, L19707 (2009).

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