Science  27 May 2011:
Vol. 332, Issue 6033, pp. 1017

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  1. A Remarkable Recovery

    A college athlete paralyzed in a hit and run accident has regained the ability to stand for a few minutes and to perform some voluntary movements, thanks to electrodes doctors fixed onto his spinal cord.

    After his injury, Rob Summers couldn't move his trunk or legs, even after 2 years of intensive physical therapy. In December 2009, surgeons at the University of Louisville in Kentucky placed a strip of electrodes on top of his spinal cord. Following a few therapy sessions in which researchers pulsed electric current through the electrodes, Summers was able to maintain a standing position with some assistance. Seven months later, he was able to stand unassisted for several minutes and could move his toes, feet, and legs on command while lying in bed. He also reports improved bladder control and sexual function, according to a 20 May case report in The Lancet.

    Other researchers say Summers's recovery is remarkable, perhaps even unprecedented. But they caution that the procedure is far from a complete cure and may not work as well for patients who are older or whose injuries are more severe.

  2. Long-Lost Tree Rat Reappears


    A rare arboreal rat wandered up to an eco-lodge in Colombia earlier this month, dumb-founding researchers who had previously searched for it in vain. “It's almost Disney-esque,” says conservation biologist Paul Salaman of the World Land Trust-US, which had conducted the search. “It found us.”

    The red-crested tree rat (Santamartamys rufodorsalis) was last seen in 1898, when a collector shot one in northern Colombia near what is now the El Dorado Nature Reserve. Six years ago, mammalogist Louise Emmons of the Smithsonian Institution's National Museum of Natural History studied the two known specimens and concluded that they represented a new genus. That inspired Salaman and others to mount a search in 2007 for the species in the reserve. They had no luck. But on the evening of 4 May, two volunteer field assistants were climbing the stairs to the reserve's ecolodge when a juvenile tree rat hopped onto the hand rail, where it curled up for 2 hours. The volunteers sent photographs to Salaman, who immediately identified it.

    Lost species of mammals are rediscovered every decade or so in South America, says Emmons. Salaman worries that feral cats may find such a tame animal an easy meal; he is sending traps to help remove the predators from the 809-hectare reserve.

  3. A Home for Curiosity?


    Scientists who next year will be searching for signs of ancient life on Mars using NASA's Curiosity rover (a.k.a. Mars Science Laboratory) spent last week in a 3-day-long huddle near the Jet Propulsion Laboratory in Pasadena, California, trying to decide where to land their rover. The workshop of about 120 scientists ended 19 May without producing a clear favorite, but NASA Associate Administrator Edward Weiler, with advice from Curiosity project leaders, will make a final decision by early July. One of four finalists is Gale Crater, constructed here from Mars imaging and other data. The target in Gale would be its 5-kilometer-high pile of sediments—or rather the bottom layers, laden with both clays and sulfates that may record the loss of an early, life-friendly environment on Mars. For images of the three other potential landing spots, visit

  4. Raising a Planetary Runt


    With a mass 11% that of Earth, Mars is decidedly undersized. But planetary dynamicists following their standard recipes for making planets have always cooked up a Mars the size of Earth or Venus. Now it appears Mars failed to grow into an Earth-size planet because it escaped prematurely from its nurturing womb of dust and rubble.

    This week in Nature, geochemists Nicolas Dauphas of the University of Chicago and his former postdoc Ali Pourmand report that Mars reached its current size lightning fast compared to our planet. Based on the steady decay of radioactive hafnium to tungsten recorded in martian meteorites, Mars stopped growing after only 2 million to 4 million years, not the tens of millions of years that Earth would have taken to agglomerate from moon- to Mars-size planetary “embryos.”

    So why did Mars grow no further? Two studies presented at March's Lunar and Planetary Science Conference in Houston, Texas, suggest that the best way to arrest Mars's development was to starve it of building material. One has Mars popping out of its rock-filled birthing grounds into such thinly populated space that it stopped growing. The other proposes that Jupiter drifted inward, carving out a gap where Mars starved, then drifted back out.

  5. From Humble Beginnings

    Llama wool and meat have long been staples among people of the central Andes. A new study suggests that a much humbler llama byproduct—dung—may have helped maize farming in the region take off, fueling the rise of ancient Andean society.

    Paleoecologist Alex Chepstow-Lusty of the Institut Français d'Études Andines in Lima took sediment cores from a lakebed some 65 kilometers northwest of Cuzco. While he was radiocarbon-dating the core's organic material and analyzing pollen trapped in the layers, he noticed the remains of small, soil-dwelling invertebrates. They were oribatid mites, which dine on dung and other detritus.

    Maize pollen first appeared in the core some 2700 years ago, at the same point that mite numbers began spiking, indicating that growing numbers of llamas and possibly alpacas were supplying manure that could be used to fertilize maize fields, Chepstow-Lusty says. As they expanded their cornfields with the help of fertilizer, the people in the Cuzco Basin amassed greater surpluses of food, allowing them to feed a large standing army and work on infrastructure such as new road networks.

    “Maize soon strips the fertility from the soils and this needs to be replenished by fertilizers,” says Chepstow-Lusty. Dung was an obvious choice to keep the farms running, he notes, and maybe that in turn helped make a more complex society possible.

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