“What is individuality” debates continue, but the scales have been tipped away from genetics somewhat by a study published this week in Science. Genetically identical mice were placed in the same complex enclosure for three months. Individual mice that explored the environment more broadly grew more new neurons than less adventurous mice. The results suggest a link between experience and brain plasticity, and that exploratory behavior may promote individuality even among genetically identical animals. “To out knowledge, it’s the first example of a direct link between individual behavior and individual brain plasticity,” said one of the researchers on the team. Not all differences are environmental, he cautions, as some mice were more prone to explore at the outset. Still, he added, “the environment amplified that difference”. Studies like this could help explain how much human individuality is based on genetic predisposition and how much is shaped by actual life experiences.