The tags, which are frequently methyl groups, control gene expression, which in turn affects how an organism behaves. Both the chemical tags and the behavior they induce appear to be reversible, says Arizona State University biologist Gro Amdam. Foraging bees, for instance, could become nurses if the hive requires it. Humans also carry epigenetic tags that may affect their behavior. Scientists found methyl groups attached to a stress-hormone-receptor gene in child-abuse victims who committed suicide. If these chemical cues can be changed in bees, scientists may find new treatments for people with psychological trauma, mood disorders, and learning disabilities too.