In 2003 about one-third of American babies between six months and two years old had watched a video from the Baby Einstein series, which promised exposure to culture, poetry, music, and foreign languages. A 2007 study reported that babies who watched the videos performed “10 percent lower on language skills” than babies who didn’t. Soon afterward, Disney spent about $100 million offering refunds to anyone who bought the videos between 2004 and 2009.

A 2006 University of Cambridge study found that meerkats teach pups how to hunt by first introducing them to dead prey, then to injured prey; when the pup is ready, the adults present them with live prey. “There were clear post-provisioning costs involved in feeding pups live prey,” the researchers wrote. If the prey escaped, the adults were able to recapture it only about 26 percent of the time. “On around 7 percent of occasions, helpers further modified the prey before returning it.”