Traditional thinking that babies are irrational and have essentially blank minds is being challenged by several recent studies that show they can make choices based on probabilities.

Last year, Fei Xu and Vashti Garcia at the University of British Columbia proved that babies could understand probabilities. Eight-month-old babies were shown a box full of mixed-up Ping-Pong balls: mostly white but with some red ones mixed in. The babies were more surprised, and looked longer and more intently at the experimenter when four red balls and one white ball out of the box — a possible, yet improbable outcome — than when four white balls and a red one were produced.