"Twin pregnancies offer 'the unique opportunity to explore social behavior before birth,' wrote researchers led by psychologist Umberto Castiello of Italy’s University of Padova. 'Newborns come into the world wired to socially interact. Is a propensity to socially oriented action already present before birth?' The researchers used ultrasound recorders to make three-dimensional videos of five pairs of twins, once at 14 weeks and again at 18 weeks. By the 14th week, they were already reaching for each other. This was even more pronounced by the 18th week, when fetuses touched each other more often than themselves."