In 1970, psychologist Gordon Gallup Jr. developed the mirror test, a measure of self-awareness. He based it in part on Charles Darwin observations. During Darwin’s visit in a zoo, he let an orangutan looked into a mirror and recorded the animal’s series of facial expressions. He noted that the significance of the expressions was uncertain. Its reactions could either mean that it could be another animal or just playing with a new toy.
To assess the animal’s self-awareness, Gallup created a test by determining whether an animal can recognize its own reflection in a mirror as an image of itself. An experiment was conducted by furtively painting the animal with two odorless dye spots. A test spot is on the part of the animal that would be visible if he faces the mirror. The other one or the control spot is in the hidden part of the body. The animal shows that it is aware that the test dye is in its own body and ignores the control dye. Observations in the absence of mirror revealed that they rarely touched the marks.
Animals that see themselves in the mirror for the first have the reaction like that of the orangutan studied by Darwin. Even people who restored their sight from blindness since birth react as if their reflection in the mirror was another person.
Orangutans, great apes, chimpanzees, gorillas, bottlenose dolphins, elephants and European Magpies some of the animals that passed the mirror test. At first gorillas were thought to have failed the test, but many studies show that they passed. Dogs, cats, and human babies all fail the test. Humans have what they call as the “mirror stage”, wherein they tend to fail the test until they are about 18 months old. Pigs also passed a variation of the test. Seven of the eight pigs were able to find the bowl hidden behind a wall using a mirror.