Snakes and spiders evoke fear and disgust in many people. Even in developed countries lots of people are frightened of these animals although hardly anybody comes into contact with them. Until now, there has been debate about whether this aversion is innate or learnt. Scientists at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in Leipzig and the Uppsala University have recently discovered that it is hereditary: Babies as young as six months old feel stressed when seeing these creatures—long before they could have learnt this reaction.