New research suggests macaques experience self-doubt and uncertainty when making decisions.
Scientists taught the macaques to play a 'fuzzy logic' game in which they had to decide whether the pixel density on a screen was sparse or dense, moving a joystick to either the letter S or D. They received a treat each time they got the right answer, but the game paused for a few seconds for each wrong answer.
However, a third option was possible. The macaques could select a question mark, moving them onto the next round without the pause. The macaques would select this when they were apparently unsure of the correct choice. This behaviour is similar to how humans behave when faced with the task. It seems the macaques are self-aware of when they are likely to make an error.
The results do not apply to all species of monkey: capuchin monkeys trained to play the same game never selected the question mark.
This finding has important implications for primate evolution. Macaques are from a lineage called old world primates, which leads to great apes and ultimately humans, whereas capuchins are from the new world primate lineage. The research raises the question of whether this self-doubting behaviour has only emerged once in primate evolution.
The research was presented last month at the American Association for the Advancement of Science (AAAS) annual meeting in Vancouver, Canada.
Watch a video of macaques playing the game here.