© Emma Collier-BakerA gibbon seems to be interested in itself, but none tried to get at icing on their own faces.
Never accuse a gibbon of vanity. The apes do not recognise their own face in a mirror, a study claims.
This stands in contrast to chimpanzees, orang-utans and perhaps gorillas, which all show a glimmer of recognition when confronted with their visage.
While primatologists may bicker over the significance of such observations, the lack of self-recognition in gibbons and other lesser apes indicates that this mental capacity emerged 14 to 18 million years ago when their evolutionary lineage split from great apes.
"We can reason about the mind of an ancestor without even laying eyes on the fossil," says Thomas Suddendorf, a psychologist at the University of Queensland, Australia, who led the study.
By comparing the anatomy, physiology and genetics of self-recognising primates with animals such as gibbons and monkeys, researchers may uncover the basis for such cognitive capacities.
Previous work had suggested that gibbons don't recognise their own mug, but those studies examined only a handful of animals of just one species of gibbon, Suddendorf says.
To make a more conclusive case for or against, he and colleague Emma Collier-Baker studied 17 different captive gibbons belonging to three out of the four existing genera.
Suddendorf's team tested self-recognition by first letting the gibbons lick tasty cake icing off their own limbs. They then painted a stripe of the same colour down the apes' faces.
With at least five hours in front of a large mirror in their enclosure, gibbons did examine the reflection and touch the glass, yet none used it to inspect whether the stripe might offer a further treat. Sometimes they even tried to reach around the mirror as if to touch a gibbon on the other side.
© Emma Collier-BakerThe gibbons sometimes tried to reach around the mirror to get at the ape on the other side.
One ape discovered the mark while scratching, but paid no more attention to it after he returned to the mirror.
They seem to have absolutely no idea that there is what looks like icing on their own face, Suddendorf says.Hot debate
"This is a nice, very detailed study, but confirms what we thought already, which is that these animals don't have mirror self-recognition," says Frans de Waal, a primatologist at Yerkes Primates Center and Emory University in Atlanta, US.
Other studies have suggested that dolphins, elephants and magpies recognise themselves.
However, Gordon Gallup, a primatologist at the State University of New York in Albany, notes that those experiments have not been replicated. Mirror self recogntion by great apes might indicate self-awareness and an acknowledgement of a personal mental state, he says.
"Creatures that are self-aware can use their experience to make inferences about comparable experiences in others," Gallup says. "Humans routinely make inferences about what other people want to know or intend to do."
Other researchers take a dimmer view of mirror self-recogntion in animals, likening it to the capacity to avoid bumping into a wall. For his part, Suddenforf thinks the signifinace of primate mirror recognition lies somewhere between those extremes, indicating an ability to entertain two models of the world - what we believe and what we observe.
Journal reference: Proceedings of the Royal Society B