This is still not completely solved issue. Besides the experiments that involved marking faces, others were devised in which the animal was urged to do something with its hand, which was hidden behind a screen, while being shown a television picture of its hand in reverse. Chimps learn to manage the task by looking at the screen and moving their hand in a trial and error strategy guided by visual feedback. Other tasks investigated whether the animal recognised itself in a video tape image, a photograph, or even its own shadow. Of course , all these experiments are behavioural tasks which cannot access the mind states of these animals directly and prove if they really do recognise themselves.
Some researchers are therefore still sceptical.
Macaques and other less intelligent primates have not yet displayed the self-recognition abilities of apes and humans. And apes that grow up with very limited social contact seem to fail too. Furthermore, developmental psychologists found evidence that self-recognition correlates with empathy. It is possible that both abilities emerge together. By the way, human babies normally learn to recognise themselves in the mirror at an age of between 12 and 20 months.