sciencehabit writes "To humans, all fire ants may look alike. But the tiny, red, stinging bugs known as Solenopsis invicta have two types of social organization, and these factions are as recognizable to the ants as rival football teams are to us. Researchers once thought that the groups' distinct physiological and behavioral profiles stemmed from a variant in a single gene. Now, a new study (abstract) provides the first evidence that the gene in question is bound up in a bundle of some 600 other genes, versions of which are all inherited together. This 'supergene' takes up a large chunk of what may be the first known social chromosome, analogous to the chromosomes that determine sex in humans."