Abstract
Drosophila form groups. I will discuss observations on genetic contributions to behaviour in groups. The data reveal two basic themes: 1) Groups affect individual behaviour and gene expression and 2) Individuals inherit elements of a mechanism that contributes to group structure, identity and the ability to discriminate members from non-members. Overall: The interplay between group – the social environment - and individuals – group members or not - sets the stage for maintaining boundaries between species.