POSTNATAL depression, which brings untold anguish to thousands of homes every year, may be a relic from the days when humans lived in caves, scientists have discovered. Researchers at Edinburgh University believe hormonal imbalances responsible for the devastating condition may have been responsible for increasing aggression in new mothers. Dr Simone Meddle, a lecturer in veterinary science, claims that in prehistoric times the change in behaviour would help to prepare mothers for protecting their young from predators. But as human life has become safer, these strong maternal instincts have become redundant. Instead, she says, the hormones may be building up...