Diversity from development When given a line to follow, some fruit flies do so carefully and others weave. Linneweber et al. now show that these behaviors are stable for an individual but diverse in an isogenic population. Key to generating individual diversity in the population is the inherent chaos of normal development. A set of neurons in the visual system is wired up in a variable manner, resulting in brain circuit asymmetry unique to each fly that guides its line-walking behavior. With more asymmetry in its brain circuit, a fly is better able to orient to the line. Science , this issue p. 1112