THEY evolved just once and have stayed much the same ever since. A study of the army ant鈥檚 DNA contradicts the view that they evolved their defining characteristics several times on different continents.
Army ants live in nomadic colonies of 50,000 individuals or more, making spectacular feeding raids en masse. Se谩n Brady at the University of California, Davis, compared nuclear and mitochondrial genes, and morphological characteristics, of 29 army ant species around the world. Brady estimates that each stems from a common ancestor living 100 million years ago on the huge supercontinent of Gondwana (Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1137809100).