Meerkat Group (IMAGE) Duke University Caption New research finds that testosterone-fueled aggression by the matriarch is a crucial part in the evolution of cooperation in meerkat societies Credit Charli Davies Usage Restrictions Please credit Charli Davies License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.