OVERVIEW

Sociobiology has come a long way. We now have a solid base of evolutionary theory supported by a myriad of empirical tests. It is perhaps less appreciated, however, that first discussions of social behaviour and evolution in Darwin's day drew upon single-celled organisms. Since then, microbes have received short shrift, and their full spectrum of sociality has only recently come to light. Almost everything that a microorganism does has social consequences; simply dividing can consume another's resources. Microbes also secrete a wide range of products that affect others, including digestive enzymes, toxins, molecules for communication and DNA that allows genes to mix both within and among species. Many species do all of this in surface-attached communities, known as biofilms, in which the diversity of species and interactions reaches bewildering heights. Grouping can even involve differentiation and development, as in the spectacular multicellular escape responses of slime moulds and myxobacteria. Like any society, however, microbes face conflict, and most groups will involve instances of both cooperation and competition among their members. And, as in any society, microbial conflicts are mediated by three key processes: constraints on rebellion, coercion that enforces compliance, and kinship whereby cells direct altruistic aid towards clone-mates.