Macaques show their ‘human’ side

“There are known knowns; there are things we know we know.

We also know there are known unknowns; that is to say we know there are some things we do not know.

But there are also unknown unknowns — the ones we don’t know we don’t know”

SO declared former US Secretary for Defence Donald Rumsfeld at a press briefing in February 2002. Being aware of one’s ignorance has always been seen as a defining human trait, but researchers in America claim that macaques also have ‘known unknowns’.

Experiments there throw new light on the evolution of ‘mind’.

Macaques are ‘Old World’ monkeys. There are 22 species, including Europe’s only non-human primate, the Barbary macaque. This famous resident of the Rock of Gibraltar is sometimes called the ‘Barbary ape’ but, although they have short tails, macaques are not apes.

Professor David Smith of State University New York and Michael Beran of Georgia State University trained macaques to play a computer game.

The animals were shown ‘pixel boxes’ on a screen. Boxes could have lots of pixels or only a few. Some were about half full. A monkey, presented with a box, could move a cursor to ‘d’ for ‘dense’ or ‘s’ for ‘sparse’. If it made the right choice it received a tasty morsel. There was no punishment for getting the answer wrong, but the appearance of the next box was delayed for several seconds.

There was, however, a Mastermind-style ‘pass’ option; a ‘don’t know’ button. If the macaque chose this, the system would present a new question without delay. A monkey in doubt, would press this in the hope of answering the next question correctly and obtaining a quick reward. Opting to ‘pass’, the researchers claim, means that the animal is aware that it can’t answer the question, a ‘known unknown’.

The ability to reflect on one’s knowledge is ‘one of the most important facets of humans’ reflective minds, central to every aspect of our comprehension and ‘learning’, David Smith told the BBC after presenting his team’s results at a recent meeting of American Association for the Advancement of Science. “These results ... could help explain why self-awareness is such an important part of our cognitive makeup and whence it came.”

We used to think that only humans were self-aware; we seemed to be the only creatures able to reflect on their own thoughts.

Then researchers forced us to admit chimps gorillas and orang-utans to the self-consciousness club.

The suggestion that macaques might be eligible for inclusion is a bit of a bombshell. We shared a common ancestor with chimps about six million years ago. The gorilla line broke away about a million years earlier. However, the Old World monkeys, to which the macaques belong, are far more distant cousins.

Their branch of the evolutionary family tree, and the one which led to the great apes, diverged around 25 million years ago.

Self-awareness, therefore, must have evolved before this split. If so, do even older monkey families also possess reflective minds?

The great division of the monkey world is between ‘Old World’ and ‘New World’ ones. The Spanish conquistadors, invading South America, came on monkeys which, they thought, looked like Capuchin friars.

These little brown primates turned out to be the most intelligent wild creatures of the New World, able not only to use tools, but to make them. Experiments in 2005 suggested that they could even grasp the concept of money. Of all the American monkey groups, the capuchins are the most likely to be able to reflect on their mental states.

However, when confronted with computer screens and pixel boxes, they never mastered the ‘don’t know’ option; there is no evidence that they have ‘known unknowns’.

The Old and New World monkey lines diverged around 40 million years ago. If self-awareness evolved only once, it probably did so sometime between then and the 25m year point and only in the Old World branch of the primate tree.

The ability was inherited by the great apes which diverged from monkeys 18m years ago, eventually leading to us. The alternative hypothesis is that consciousness evolved independently in several Old World lines but not in New World ones, which seems implausible.

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