Birth of the beat

Music’s roots may lie in melodic exchanges between mothers and babies

At scientific meetings, psycho-biologist Colwyn Trevarthen often plays a video of a 5-month-old Swedish girl giving her mother a musical surprise. Blind from birth, the girl reaches for a bottle and laughs appreciatively as her mother launches into a familiar song about feeding blueberries to a bear. As in baby songs everywhere, Trevarthen says, each line of the Swedish tune runs about four seconds and each stanza lasts about 20.