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In the News

This roundup summarizes some notable recent items about scientific research, selected from news reports compiled in Sigma Xi’s free electronic newsletters Science in the News Daily and Science in the News Weekly. Online: and

Altruism on the Brain

People with heightened altruistic tendencies probably have a greater-than-normal ability to perceive purposeful action in others and to empathize with them. Because perception of such “agency” in others is known to correlate with activation of the posterior superior temporal cortex, two investigators hypothesized that functional MRI would reveal especially large amounts of activity in this part of the brain when an altruist perceives the actions of another agent. Two experimental trials, each involving about two dozen subjects, confirmed the prediction, at least in general terms.

Tankersley, D., C. J. Stowe and S. A. Huettel. Altruism is associated with an increased neural response to agency. Nature Neuroscience 10:150–151 (February)

Piscine Pecking Order

Male fish of the species Astatotilapia burtoni regularly fight with one another as rivals for territory. Those that lose in such bouts descend the social ladder, losing their normally bright coloration and becoming reproductively dormant. To test whether such fish could demonstrate a form of reasoning known as transitive inference, investigators from Stanford University placed one fish in the central compartment of an all-glass tank and allowed it to view pairwise clashes between a total of five rivals. The experiment was manipulated so that the five fish on display won or lost their battles according to a prescribed pecking order, with fish A beating fish B, who in turn conquered fish C, who dominated fish D, who could rough up fish E. What these investigators found was that a spectator fish could use its observations to discern the overall ranking. They determined that such reasoning was going on, because when they put the spectator in a tank that contained two other fish, the spectator would consistently gravitate toward the weaker one, even when it had not seen those particular two rivals in battle together. That is, it could not draw on its memory of past bouts to determine which of the two others it would be best to steer clear of. Instead, the fish had to determine that using transitive inference, an ability that animal behaviorists formerly believed that only primates, rats and birds could boast.

Grosenick, L., T. S. Clement and R. D. Fernald. Fish can infer social rank by observation alone. Nature 445:429–432 (January 25)

Arms and the Chimp

Investigators studying wild chimpanzees have long observed these animals using tools for various purposes: stones to pound open nuts, say, or thin stalks of grass to lure termites out of their mound. But two anthropologists have now discovered that chimps also make and use tools for hunting—an ability that was formerly thought to be uniquely human. The epiphany came from their observation of Senegalese chimps that fashioned branches into crude spears, removing the smaller side branches, leaves and sometimes the bark, and then sharpening the tips with their teeth. The chimps then forcibly jabbed these weapons into hollow branches and trunks in an effort to skewer anything that might be hiding inside. The investigators observed this behavior 22 times and in one instance saw how it served to immobilize the chimp’s prey, a bush baby (a small noctural primate), which the hunter then extracted and ate.

Pruetz, J. D., and P. Bertolani. Savannah chimpanzees, Pan troglodytes verus, hunt with tools. Current Biology 17:1–6 (March 6)

Clouds of Rock?

Astronomers have succeeded in probing the atmosphere of a very distant world, extra-solar planet HD 209458b. They did so by aiming the Spitzer Space Telescope on the planet as it was passing in front of its parent star (which this “hot Jupiter” orbits closely) and also while the planet was out of view behind the star. Then, by subtracting the second set of measurements from the first, they were able to generate a spectrum that was representative of the planet’s searing atmosphere. One spectral peak delineated in this way suggests that HD 209458b may be covered in clouds of silicate material—that is, the stuff of rocks. Another spectral feature, the astronomers tentatively suggest, may signal the presence of polycyclic aromatic hydrocarbons.

Richardson, L. J., D. Deming, K. Horning, S. Seager  and J. Harrington. A spectrum of an extrasolar planet. Nature 445:892–895 (February 22)

Rebel with a Cause: Allopregnanolone

Although popular wisdom attributes the mood swings of teenagers to raging sex hormones and the stressful psychological changes of puberty, neuroscientists are now offering a new explanation: a brain chemical called allopregnanolone. In adults, this stress hormone reduces anxiety by targeting certain receptors on brain cells, but experiments with mice suggest that it may act quite differently in adolescents, increasing brain activity to produce a state of heightened anxiety.

Shen, H., Q. H. Gong, C. Aoki, M. Yuan, Y. Ruderman, M. Dattilo, K. Williams and S. S. Smith. Reversal of neurosteroid effects at σ4β2δ GABAA receptors triggers anxiety at puberty. Nature Neuroscience (Published online March 11)

Ancient-Bird Biplane

A recent study of Microraptor gui, a 1-kilogram dromaeosaur, helps to answer the question of how birds evolved their ability to fly. This feathered creature lacked a structure called the supracoracoideus pulley and thus could not elevate its wings. So it probably could not take off from the ground and must have used its wings only for gliding. What’s remarkable is that its wings were staggered, with those attached to the feet positioned lower and somewhat farther back, much like the arrangement found in a typical biplane.

Chatterjee, S., and R. J. Templin. Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui. Proceedings of the National Academy of Sciences of the U.S.A. 104:1576–1580 (January 30)

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