low-ranking mums live life on perpetual high alert. They must watch as their offspring are confronted by dangerous group members, yet are powerless to do anything about it. As their innate warning system screams, their anxiety increases exponentially in the face of social inequality. This stress, detected in the hormones excreted in their faeces, is thought to lower their immune response and make mothers more vulnerable to disease. It can also manifest as depression and even infant abuse. Humans are not the only primates to suffer from post-natal depression.
