SCIENCE

Notebook

Babies Grasp Concepts

Five-month-old babies can comprehend concepts for which they have not yet learned words, suggesting that some types of thinking precede language, researchers have found.

A simple experiment probed what has become one of the most complex questions in psychology -- the role of language in learning. Some scholars believe language directs the ways people think, so that learning one language produces a different conceptual view of the world than learning another language.

Susan J. Hespos at Vanderbilt University and Elizabeth S. Spelke at Harvard University found that 5-month-old babies being reared in English-speaking homes were able to grasp the difference between a loose fit and a tight fit -- putting a pencil into a plastic cup, for instance, versus stacking a second cup inside the first.

That difference is emphasized by Korean but not by English. By showing that babies growing up in English-speaking homes are sensitive to the distinction, the researchers demonstrated that some forms of thinking do precede language.

Babies can learn any language but eventually lose the ability to detect foreign sounds -- this is partly why it is difficult to learn a second language at an older age. The same idea may apply to concepts, said psychologist Paul Bloom at Yale University, in an editorial published along with the new research in last week's issue of the journal Nature -- babies in different cultures acquire meaning that is of most relevance to their contexts.

There is one crucial difference, however: Adult English speakers can tell the difference between a loose fit and a tight fit. Unlike sounds, Bloom concluded, humans do not lose the ability to learn distinctions in meaning.

-- Shankar Vedantam

Surviving Amid the Glaciers

Over the last 2 million years, glaciers have advanced and retreated over parts of North America more than 20 times. The classic sequence of events has animal species migrating south as the ice advances, sojourning in temperate regions for thousands of years and repopulating the scoured land when the ice retreats.

A team of biologists from Illinois and Michigan now has evidence that some mammals survived the last glacial onslaught 18,000 years ago in place. They were not, of course, under the ice but in rare, ice-free patches known as "driftless regions."

Evidence for this scenario resides in the genes of a species of chipmunk, Tamias striatus.

Kevin C. Rowe of the University of Illinois in Urbana and his collaborators collected 244 animals from 25 sites in Wisconsin, Illinois, Indiana and Michigan. They clipped a bit of ear skin from each animal for genetic tests.

Chipmunks in Wisconsin had a distinctive genetic profile and had very close relatives to the south and east in Illinois and Indiana. Sprinkled throughout the latter area, however, were numerous other populations of T. striatus, both different from each other and from the Wisconsin animals.

Using the genetic differences as a "molecular clock," the researchers showed that the Wisconsin chipmunks and their "wisconsinoid" relatives to the south and east shared a common ancestor less than 50,000 years ago -- about the time of the last Ice Age. However, those animals and the other T. striatus chipmunks in the region had not shared a common ancestor for at least 130,000 years -- from the time of an earlier Ice Age.

This and other observations suggest the Wisconsin chipmunks spent the last Ice Age on their ancestral ground. When it was over, they sent descendants south to colonize open land that was simultaneously being filled by more distant cousins moving north.