Are kids born kind or do we need to teach them kindness? This nature versus nurture debate is an old one, but new findings published last month in the journal PLoS ONE may provide some novel insights.

The study, by Lara Aknin and her colleagues in the psychology department at the University of British Columbia, builds on the idea that if altruism is a deeply rooted part of human behavior, serving an evolutionary purpose, we’d find kind, helpful—or “prosocial”—acts intrinsically rewarding from the earliest stages of life, even when these acts come at a personal cost. In other words, performing selfless acts would make kids happy—even before they’ve been socialized to fully appreciate the cultural value placed on kindness.

Encouraged by the results of a preliminary study they ran, which showed that toddlers who shared a toy with someone else appeared happier than toddlers who simply played with the toy, the researchers developed a more elaborate experiment. Twenty toddlers, all a month or two shy of their second birthday, were introduced to a monkey puppet who, they were told, “liked treats.” Soon afterward, an experimenter “found” eight treats—either Teddy Grahams or Goldfish crackers—and gave them to the toddler, saying all the treats belonged to that child

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