A Brigham Young University study indicates that 5-month-old babies can distinguish upbeat tunes from sad compositions and that by nine months they can pick out a bummer song from a set of happy pieces. BYU psychology professor Ross Flom says:

One of the first things babies understand communicatively is emotion, so for them the melody is the message.

Flom's study is fascinating, but I can see academic challenges to his data — mainly because the researchers used classical music, songs like "Ode to Joy" from Beethoven's Ninth Symphony to test the happy reflex, against downers like Beethoven's Seventh Symphony.

It's only reasonable to assume that some of the babies — even at BYU — are undeveloped headbangers who would prefer to rock out to, say, AC/DC's upbeat "Highway to Hell" or old-school tots who would lock in on Chuck Berry's emotionally ambiguous "Maybellene."