Babies as young as six months can tell the difference between good and bad behaviour, according to a study at Yale University in which infants appeared to warm to helpful characters.
Babies were placed in front of a display showing a hill on which wooden characters were moved up and down. One character, the "climber", was either helped to the top by a triangular-shaped "helper", or hindered by a square one called "bad".
All 12 of the six-month-old babies preferred the "helper" character and 14 of the 16 ten-month-olds chose the helper.
The American scientists, writing in the journal Nature, said: "The presence of social evaluation so early in infancy suggests that assessing individuals by the nature of their interactions with others is central to processing the social world, both evolutionarily and developmentally."