New DNA studies by Cornell researcher Sean Brady have shown that army ant swarming behavior is so successful at ensuring them food that evolutionary pressures have not changed the army ant’s genetic makeup in over 100 million years. Brady studied the DNA of 30 army ant species and 20 possible ancestor species, divided between the New World (South American) species in Ecitoninae and the Old World (African/Australian) groups Aenictinae and Dorylinae. He specifically sought information from four different genes to uncover clues to their relationships. Combining this data, Brady found that all the species share some of the same genetic mutations. “If they share those mutations, we can infer they evolved from the same source,” he said. In other words, army ants evolved only once, sometime before breakup of the supercontinent Gondwana into Africa and South America about 100 million years ago, and essentially haven’t evolved since then. Brady’s paper, “Evolution of Army Ant Syndrome: The Unique Origin and Long-Term Evolutionary Stasis of a Novel Complex of Behavioral and Reproductive Adaptation,” will be published soon in PNAS and on the Web here.

“I didn’t think they’d be that old. … It’s kind of amazing that for tens of millions of years they were engaged in their hunting parties when dinosaurs were walking all over them,” Brady said.