An alternative theory is that we have evolved just to be good at distinguishing changing facial expressions (and body language), especially within our own socia

An alternative theory is that we have evolved just to be good at distinguishing changing facial expressions (and body language), especially within our own social groups. Using this skill to match people's expressions with their behavior over time would give us a tool for making good predictions. But if we then met a complete stranger or tribe whose face at rest, say purely through random variation of bone structure, happened to look more aggressive or happier or more sneaky than the resting faces of our friends, it would lead us to make biased and unjustified predictions.