One of the most effective ways to teach children to do anything is a process we refer to as ‘modelling’. As a species, we are especially good at copying others, and children, with their spongelike brains, take in all sorts of behaviour and information in this way.
From dance crazes to sayings and from hairstyles to how they sit at the dinner table, our children are watching and learning. It is not a conscious process for them, it is without thought; they take in what they are seeing and hearing and regurgitate it as their own. The facial expression that you thought was hereditary is not, it is learnt. Yes, nature does play a part in some things, but nurture is a very powerful process in children learning.