We are interested in understanding the genetic basis of heritable behavioral variation. In the current age, it has become cheap and easy to catalog the set of genetic differences between two individuals. But which genetic differences are responsible for generating differences in innate behaviors, including liability to neurological diseases such as autism, bipolar disease, and schizophrenia? How do these causative genetic variants modify a nervous system? Besides their role in disease, genetic variation is the substrate for natural selection. To understand how behavior evolves, we must understand how it varies.