Babies as young as eight months old prefer it when people who commit or condone antisocial acts are mistreated, a new study led by a University of British Columbia psychologist finds.

While previous research shows that babies uniformly prefer kind acts, the new study published Nov. 28 in the Proceedings of the National Academy of Sciences suggests that eight month-old infants support negative behavior if it is directed at those who act antisocially -- and dislike those who are nice to bad guys.

"We find that, by eight months, babies have developed nuanced views of reciprocity and can conduct these complex social evaluations much earlier than previously thought," says lead author Prof. Kiley Hamlin, UBC Dept of Psychology, who co-authored the study with colleagues from Yale University and Temple University.

"This study helps to answer questions that have puzzled evolutionary psychologists for decades," says Hamlin. "Namely, how have we survived as intensely social creatures if our sociability makes us vulnerable to being cheated and exploited? These findings suggest that, from as early as eight months, we are watching for people who might put us in danger and prefer to see antisocial behavior regulated."

For the study, researchers presented four scenarios to 100 babies using animal hand puppets. After watching puppets act negatively or positively towards other characters, the babies were shown puppets either giving or taking toys from these "good" or "bad" puppets. When prompted to choose their favorite characters, babies preferred puppets that mistreated the bad characters from the original scene, compared to those that treated them nicely.

The researchers also examined how older infants would themselves treat good and bad puppets. They tested 64 babies aged 21 months, who were asked to give a treat to, or take a treat away from one of two puppets -- one who had previously helped another puppet, and another who had harmed the other puppet. These older babies physically took treats away from the "bad" puppets, and gave treats to the "good" ones.

Hamlin, who conducted the research with Karen Wynn and Paul Bloom of Yale University's Dept. of Psychology, and Neha Mahajan of Temple University, says the findings provide new insights into the protective mechanisms humans use to choose social alliances, which she says are rooted in self-preservation.

Hamlin says the infant responses may be early forms of the complex behaviors and emotions that get expressed later in life, such as when school children tattle on kids who break the rules, the rush people feel when movie villains get their due, and the phenomenon of people cheering at public executions.

Hamlin says while such tendencies surely have many learned components, the fact that they are present so early in life suggests that they may be based in part on an innate foundation of liking those who give others their "just desserts."