Martha (right), an extinct passenger pigeon, at the Smithsonian's Natural history Museum in Washington. The passenger pigeon was once the world's most plentiful bird. Sept. 1 is the centenary of the bird's extinction. Susan Walsh/AP hide caption

itoggle caption Susan Walsh/AP

Lindolfo Carballo, an immigrant from El Salvador, meets his son Raynel outside school. In El Salvador, he says, families often "teach their boys one thing and their girls differently." He's trying to set a different example for his children. Sarah Tilotta for NPR hide caption

itoggle caption Sarah Tilotta for NPR

A recent study found a brief delay in peak growth spurt among boys who took ADHD stimulants for at least three years, but no significant effect on their ultimate height. iStockphoto hide caption

itoggle caption iStockphoto

The Ricketts family poses on the Chicago Cubs field in 2010, a year after they bought the team. From left, Laura Ricketts, Joe Ricketts, Marlene Ricketts, Todd Ricketts, Tom Ricketts and Pete Ricketts. Nam Y. Huh/AP hide caption

itoggle caption Nam Y. Huh/AP

Third-year medical student Allie Tetreault, left, talks with Gabrielle Nuki, 16, at Maine Medical Center in Portland, Maine. Gabrielle helps med students practice patient care. Patti Wight/MPBN hide caption

itoggle caption Patti Wight/MPBN

Tony Stewart, driver of the #14 Bass Pro Shops / Mobil 1 Chevrolet, hits the wall on the backstretch during the NASCAR Sprint Cup Series Oral-B USA 500 at Atlanta Motor Speedway on Sunday in Hampton, Ga. Jamie Squire/Getty Images hide caption

itoggle caption Jamie Squire/Getty Images

Long time employees Denise Miller, facing camera, and Gloria Panameno hug as they leave the Showboat Casino Hotel on Sunday. Owner Caesars Entertainment closed the still-profitable Showboat to reduce the number of casinos in Atlantic City, which has been struggling with plunging revenue. Mel Evans/AP hide caption

itoggle caption Mel Evans/AP