Can an army of babies and dogs rescue psychology from its reproducibility crisis?

Baby Zoe sits on her mother’s lap and watches a puppet show featuring three shapes with googly eyes. A red circle struggles to climb a steep hill until a blue square helps it with a push. A yellow triangle blocks the way and shoves the red circle down the hill. When the show is over, Zoe is offered a choice of puppets. She doesn’t hesitate: she ignores the unkind yellow triangle and makes a grab for the helpful blue square. The scene, from a Netflix documentary series released in 2020, recreates a highly cited 2007 study 1 , which found that babies as young as six months old overwhelmingly prefer characters who help, rather than hinder, others. On the basis of these findings, developmental psychologist Kiley Hamlin, now at the University of British Columbia in Vancouver, Canada, concluded that the ability to evaluate others’ behaviour develops before speech, and could be a biological adaptation. Over the next decade or so, researchers performed dozens of versions of Hamlin’s experiment. But many of them failed to find the same preference for helpers — or suggested that other factors could explain the choice. Hamlin became frustrated at the resulting confused picture, so, in 2017, she assembled a collaboration of 37 research groups in 18 countries to repeat the experiment with more than 1,000 babies. That, she thought, should settle the matter once and for all. …