We take it for granted when we look in a mirror we see ourselves staring back but this actually requires quite a lot of brain power. Infants don't recognise themselves until they are around 18 months and only a few animals apart from humans are capable of it at all. This phenomenon struck me at Halloween when my 2 year old daughter was having her face painted and whilst she knows her own reflection the look of shock and bewilderment on her face when she looked in a mirror and saw a cat version of herself had us in hysterics.
Unfortunately the system of self recognition can go wrong in a variety of illnesses such as Alzheimers Disease, schizophrenia and following a brain injury or stroke. The inability to recognise yourself can lead to beliefs (delusions) that someone else exists within the mirror.
In animals it is obviously harder to test their ability to recognise themselves in mirrors. Researchers have found evidence for some aspects of self-recognition in chimpanzees, gorillas and bottlenosed dolpins amongst a few others. However the results are not clear cut and even in chimps the most studied only 75% of adults show a response.
So the next time you look in the mirror instead of pondering your own beauty give a thought to the complexity of the brain which allows you to pick that spot or apply that lipstick.