Meerkats, like wolves, live in communities in which only the dominant animals reproduce, but all members of the group help rear offspring. Exactly how the dominant animals achieve this reproductive monopoly has eluded explanation, but now scientists have found evidence that the dominant females use aggression to suppress their subordinates' reproductive systems. Researchers report that when pregnant, dominant meerkat females selectively chase and attack individuals who pose the greatest reproductive threat (older, pregnant or distantly-related females), driving them from the group for an average of three weeks at a time. The evicted subordinates exhibit a marked increase in stress hormones, which leads to reduced conception rates and increased abortion rates. The research, published in this week's Proceedings of the National Academy of Sciences, is the first clear evidence to date of stress-related reproductive suppression in cooperatively breeding animals.