Unlike chimpanzees, orang-utans and gorillas, apes do not recognise their own face in a mirror, a new study has found.
According to scientists, the lack of self-recognition in gibbons and other lesser apes indicates that the mental capacity emerged 14 to 18 million years ago when their evolutionary lineage split from great apes, reports New Scientist.
"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.
Earlier studies 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 said.
To put an end to the speculation, he and colleague Emma Collier-Baker studied 17 different captive gibbons belonging to three out of the four existing genera.
The research 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.
One ape discovered the mark while scratching, but paid no more attention to it after he returned to the mirror.
According to Suddendorf, apes didn't seem to have an idea that there is what looks like icing on their own face.
"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.
The study has been published in Proceedings of the Royal Society B.