In the News
Rats Reveal a New Talent: "Stereo Smell"
Rats' nostrils are only 3 millimeters apart, but they appear to use
them independently, localizing the source of an odor much as humans
locate the source of a sound. Biologists in Bangalore trained rats
to respond to odors on their left or right by drinking from a
corresponding water spout. The rats required only 50
milliseconds—a single sniff—to make the decision, with
80 percent accuracy. When one nostril was covered, the localization
ability was lost, which implies that rats' brains normally compare
the signals from each nostril in order to create a spatial
understanding of the environment.
Bhalla, U. Rats smell in stereo. Science
311:666–670 (February 3).
Master Genes More Likely to Mutate in Humans than Chimps
The figure is familiar: A whopping 99 percent of human genes are the
same as those found in chimpanzees. Conspicuous diversities in the
face of all that genetic compatibility have puzzled geneticists for
as long as they have known the number. Now scientists have
determined that many of the genetic mutations that differentiate
people from chimps have occurred in master genes. These key genes
regulate arrays of other genes by switching them on and off,
resulting in lots of evolutionary bang for the buck. In liver tissue
taken from humans, chimps, orangutans and rhesus macaques, genetic
mutations among the regulatory genes were four times more likely to
occur in humans than in the other primates.
Gilad, Y., et al.Expression profiling in primates
reveals a rapid evolution of human transcription factors.
245 (March 9).
Otterlike Fossil Challenges Timetable of Mammal Evolution
A new Chinese fossil find lends support for a dramatic revision of
the evolution of early mammals. Paleontologists had believed that
only small shrewlike creatures had coexisted with the dinosaurs and
that larger mammals did not emerge until the giant reptiles died out
65 million years ago. But the remains of a foot-long fur-bearing
aquatic mammal, Castorocauda lutrasimilis, show that larger
mammals existed 164 million years ago. The new fossil, which had a
beaver's tail and a seal's teeth, was found in Inner Mongolia's
Ningcheng county, northeast of Beijing.
Ji, Q. A swimming mammaliaform from the middle Jurassic and
ecomorphological diversification of early mammals. Science
311:1123–1127 (February 24).
Ponder Unconsciously for the Best Decision
If you're faced with a complex decision, the best course may be to
focus on another task and let your unconscious work it out—or
even simply to follow your first impulse.
That's the conclusion of a new study that tried to uncover the
relationships among a decision's complexity, the amount of time
spent consciously deliberating about it and the subject's final
satisfaction. In choosing which of four hypothetical cars to buy,
students chose well when they consciously considered a list of four
attributes, such as leg room and mileage. When that list was
increased to 12 attributes, however, better decisions were reached
by a group of students who were asked to do distracting puzzles
instead of thinking about the choice.
Dijksterhuis, A. On making the right choice: The
deliberation-without-attention effect. Science
311:1005–1007 (February 17).
After Robins Fly South, Mosquitoes Spread West Nile Virus
Monitors of the West Nile virus in America should watch for the late
summer-early fall departure of the red-breasted robin. The robin is
the favorite food source of the Culex pipiens mosquito,
which carries the virus. In the birds' absence, the mosquitoes turn
to humans. A study has found that mosquitoes feed on people at a
rate seven times higher in the late summer than they do in the early
summer. In fact, the number of human cases of West Nile in the U.S.
is highest in the months of August and September.
Kilpatrick, A. M. West Nile virus epidemics in North America are
driven by shifts in mosquito feeding behavior. PLoS Biology
Geysers on Saturn's Moon Enceladus
Saturn's moon Enceladus contains geysers that spout icy crystals, a
strong suggestion that liquid water lurks in pools beneath the
surface. The phenomenon adds Enceladus to the solar system's really
short list of places that could conceivably host life. The geysers
turned up in images taken by NASA's Cassini spacecraft as it buzzed
by the moon's south pole. Astronomers had believed that Enceladus,
only 300 miles wide, was likely a frozen piece of rock. Instead, the
new observations show that it potentially possesses all of the
elements that life needs to exist—water, relative warmth and
Porco, C. Cassini observes the active south pole of
Enceladus. Science 311:1393–1401 (March 10).
Immunity Linked to Brain Growth
Scientists have found evidence that bolstering the immune system may
also shore up the brain against the onset of age-related learning
and memory problems. The culprit: T-lymphocytes, cells that course
through the blood stream attacking invaders. The cells were believed
to act the same way in the brain, but it turns out that they may
perceive a whole host of things they encounter in the brain as
infectious, including normal brain proteins. The study posits that
when T-lymphocytes misjudge these normal proteins, they begin to
produce microglia, cells that promote inflammation. In the
brain—particularly in the hippocampus, the seat of learning
and memory—the microglia have the added benefit of boosting
the development of new neurons.
Ziv, Y., et al. Immune cells contribute to the
maintenance of neurogenesis and spatial learning abilities in
adulthood. Nature Neuroscience 9:268
275 (February 1)