Researchers report that female monkeys are chattier than males, adding weight to the theory that human language evolved to strengthen social bonds. Scientists in the UK studied the vocal exchanges of a group of 16 female and 8 male macaques for 3 months to test the theory that language developed in humans as a less time-consuming way to maintain close bonds. After counting the grunts and coos between the macaques, the team found that the females made 13 times as many friendly noises as the males. This is the first time that sex differences in communication have been identified in non-human primates. [New Scientist ]