:: By Megan Lisagor

:: Photography by Susan Kidwell

Investigations ::

Shell power

The shell still has pride of place among paleontologists and evolutionary biologists. Putting its fossil record to the test, Susan Kidwell, the William Rainey Harper professor of geophysical sciences, examined marine bivalves, a group of shellfish that includes scallops, oysters, and mussels. Differences in composition among lineages, Kidwell found, have not caused distortions in the bivalve record, as some researchers had predicted. Thus, she reports in the February 11 Science, it continues to offer a reliable picture of evolutionary history.

Graduation inflation

Only about half of Chicago public high-school students graduate in four years, a study released in February revealed. Although the rate has improved since the early 1990s, it remains well below the 71 percent city officials had earlier claimed. In fact, only 54 percent of freshmen entering in 1999 earned diplomas in 2004, reports Elaine Allensworth, associate director of the Consortium on Chicago School Research. Allensworth, who attributes the government’s numbers in large part to ignoring transfer students who drop out, found that African American boys fare the worst—only 39 percent graduate by age 19, compared with 51 percent for Latinos, 58 percent for whites, and 76 percent for Asians.

Steal-estate agent

As some homeowners may have suspected, real-estate agents sometimes push clients to close a deal too quickly to speed up earning their commissions, Steven Levitt, the Alvin Baum professor of economics, and assistant professor Chad Syverson report in a study released in January. Agents earn only a shred of any incremental profit, so there’s little financial incentive to prolong the selling process. How do they get away with it? Their clients don’t know any better. Levitt and Syverson recommend hiring an appraiser before signing on the dotted line. After all, the economists found, agents keep their own digs on the market about 9.5 days longer and sell them for about 3.7 percent more.

Handy math

Instruction + gesture = math comprehension. That’s according to an analysis of 160 elementary-school students by Susan Goldin-Meadow, the Irving B. Harris professor of psychology, and Melissa Singer, AM’97, PhD’04. Given arithmetic problems to solve, the kids learned better when the teacher provided a verbal explanation and used hand motions, Goldin-Meadow and Singer report in the February Psychology Science. Oddly enough, the effect was greatest when the instruction and gesturing weren’t coordinated.

Get active

An enriched environment may help prevent Alzheimer’s disease, a team led by Sangram Sisodia, director of the Center for Molecular Neurobiology, confirms in the March 11 Cell. The researchers studied mice genetically predisposed to the disorder, raising some in deluxe accommodations—large cages complete with running wheels, tunnels, and toys—and others in basic quarters. After five months, they found, the mice with the perks had lower levels of the peptides characteristic of the disease in their brains and blood. Mental and physical activity, the team concluded, are key to thwarting its onset.