Every mother knows that newborns are social creatures just hours after birth. They prefer to look at faces over objects, and they even imitate facial expressions. Now a study sug­gests that the propensity for social interactions exists in the womb. Twins begin interacting as early as the 14th week of gestation.

Researchers at the University of Turin and the University of Parma in Italy used ultrasonography, a technique for imaging internal body structures, to track the motion of five pairs of twin fetuses in daily 20-minute sessions. As published in the October PLoS ONE, the scientists found that fetuses begin reaching toward their neighbors by the 14th week of gestation. Over the following weeks they reduced the num­ber of movements toward themselves and instead reached more frequently toward their counterparts. By the 18th week they spent more time contacting their partners than themselves or the walls of the uterus. Almost 30 percent of their movements were directed toward their prenatal companions. These movements, such as stroking the head or back, lasted longer and were more accurate than self-directed actions, such as touching their own eyes or mouth.

The results suggest that twin fetuses are aware of their counterparts in the womb, that they prefer to interact with them, and that they respond to them in special ways. Contact between them appeared to be planned—not an accidental outcome of spatial proximity, says study co-author Cristina Becchio of Turin. “These findings force us to predate the emergence of social behavior,” she says.