Random Samples

Science  06 Apr 2007:
Vol. 316, Issue 5821, pp. 27


    Two-thirds of all cities with populations exceeding 5 million are “especially vulnerable to risks resulting from climate change,” according to a study from Columbia University and the International Institute for Environment and Development in London. A team of geographers defined danger zones as areas within 10 meters above sea level, the places most vulnerable to weather oscillations combined with the 25- to 60-cm sea-level rise forecast by 2100. China (see map) is in the lead, with 144 million people, or 11% of its population, at or below the 10-meter level. The world's poor are the most imperiled, with some 247 million at risk in least developed nations. Numbers will climb with continued urbanization, note the authors, who say nations should develop policies to encourage inland growth.

  2. NETWATCH: Ins and Outs of Carbon

    Some parts of the world pump more carbon dioxide into the atmosphere than they remove, whereas other regions are net absorbers. A new site for charting the ups and downs of the greenhouse gas is CarbonTracker from the U.S. National Oceanic and Atmospheric Administration in Boulder, Colorado.

    CarbonTracker incorporates CO2 measurements from some 60 locations around the world to provide a broad picture of carbon uptake and release for North America, the globe, and the oceans between 2000 and 2005. Visitors can also check out the “carbon weather” to see how storms alter levels of the gas. The researchers hope other labs will contribute data that could help make CarbonTracker an objective tool for gauging whether carbon emission targets are being met.



    Before and after. CREDIT: T. BROMAGE

    Homo rudolfensis, a 1.9-million-year-old skull from Kenya, may not be a Homo after all, says a scientist who has done a computer reconstruction of the skull.

    The skull fragments—found in 1972 near Lake Turkana and put together by Richard Leakey—have sparked much debate, because their owner seemed to have had a much larger brain than other hominids of similar age.

    Now Timothy Bromage, a paleoanthropologist and expert on facial bone development at New York University, claims to have sorted out the puzzle. In a virtual reconstruction, he followed a rule that he says applies to all primates: The angle created by drawing a line from the eye socket to the ear and then to the top back molar is always 45°. Shifting the skull bones to conform to the rule pushes out the lower face and leads to a much smaller brain: about 575 cubic centimeters instead of the 752 found by Columbia University anthropologist Ralph Holloway. That downsizing along with the newly prognathous profile just about edge the skull out of the Homo ballpark, Bromage told a meeting of the International Association for Dental Research last week in New Orleans, Louisiana.

    Holloway says he's sticking to his own estimate. “I sincerely doubt that these fragments can be so radically reconstructed,” he says. “Maybe with a computer, but not by a trained anatomist's hand.” But paleoneurologist Dean Falk of Florida State University in Tallahassee says she thinks Bromage's method for hafting faces onto crania is “really exciting. … We're exploring applying it ourselves.”



    Toxoplasma gondii is a parasite that requires two hosts. It's born in a cat's intestines, develops in another animal—such as a rat—and must return to a cat to reproduce. To boost its chances of making that return trip, researchers at Oxford University have shown, Toxoplasma makes rodents less afraid of cats. Now a Stanford University team led by Ajai Vyas has found that rats carrying the parasite don't mellow out across the board; they just lose their fear of the smell of cats.

    In the lab, infected rats showed much less aversion than normal ones to bobcat urine. But they reacted normally when the researchers probed other types of fear responses. That means Toxoplasma has a “remarkably specific” behavioral effect, says co-author Robert Sapolsky. He says most parasites control behavior in much cruder ways—for example, by destroying muscle metabolism so an organism can't evade a predator. In the 2 April online Proceedings of the National Academy of Sciences, the scientists report that Toxoplasma cysts form preferentially on the rat amygdala, which Sapolsky calls “ground zero” for fear in the brain.

    “I always found it incredible that the parasite would be able to alter a response, cat aversion, that is so ingrained in the rat's psyche,” says Oxford veterinary scientist Manuel Berdoy, an author of the earlier work. He says the new research shows that the parasite may have the “astonishing” ability to zero in on the neural pathways for processing cat odors.