Evidence has shown that only humans and great apes have self-recognition – the ability to recognise themselves in a mirror – a cognitive facility that has so far eluded the common monkey. This finding is supported by research spanning over 40 years and is rarely disputed. But how do you actually test which great apes or monkeys can recognise their own reflection? It is fairly easy to tell when a monkey cannot recognise themselves when obvious signs occur such as displays of aggression and intimidating behaviour towards their own reflection. However, confirming whether an ape has recognised their own reflection can be much more difficult. For all we know they may be perfectly aware of their reflection but just take no action. Researchers have tried to overcome this problem by placing small red dots on areas of particular interest to the apes, primarily on the face, ears and genitals (this is known as a ‘marks test’). The identification of these foreign marks and subsequent investigation of these areas of interest implies self-recognition. It had previously been hotly debated whether monkeys possessed these same self-recognition abilities. This debate arose from a group of rhesus monkeys who used a mirror to identify and investigate an acrylic block (taking neurophysiological measurements for another study) which had been implanted in their skull. However, these monkeys failed to show self-recognition on the traditional marks test and it was argued that the monkeys were just interested in the painful weight on their head (understandably) and that this investigation of the head just happened to coincide with an experiment in front of a mirror. So despite their best efforts, monkeys still seem to be playing cognitive second-fiddle to the great apes and their red-marked heads, ears and genitals.[/note]Anderson, J.R., Gallop, G.G, Jr. 2010. Which primates recognise themselves in mirrors? PLoS Biol 9(3) e1001024.[/note]