Whenever we decide to throw a party, invite in-laws to dinner or embark on a cruise, we are driven by the most basic component of social behavior: The desire to hang out with other humans. Considering that the drive to form groups with members of one’s own species has been conserved throughout evolution, it’s evident that social behavior is governed by genes, at least to some degree. But our parents and teachers help us hone our social graces, so teasing apart the effects of nature and nurture on this behavior is hard, if not impossible. By studying zebrafish, Weizmann Institute of Science researchers, in collaboration with scientists in Portugal, have managed to solve part of the riddle of how social behavior is hardwired into the developing brain.