The first proof that non-human primates (gorillas and orangutans) can distinguish and categorize other species like humans can was presented in the Sept. 10, 2013, edition of the journal PeerJ by Dr. Jennifer Vonk with Oakland University in Rochester, Michigan.
The capacity to categorize other species or objects based on physical attributes and similarity was previously considered to be a trait specific to humans only.
The researchers tested a young female gorilla and four orangutans in two separate experiments. The animals were shown photographs of other animal species and were required to attempt to match the images to images of the same species or family of animals. The second experiment presented photographs of a variety of animal species and required the test primates to designate the photographs as being similar to photographs of the same species.
The trials were designed to test the existence of perceptual similarity and categorization as displayed in humans.
The primates were not as facile as humans in matching images correctly using only perceptual strategies but produced equivalent facility as humans with practice. Categorization was more readily apparent in orangutans than gorillas.
The researchers postulate that the ability to categorize objects in humans may be an evolutionary development from primates. The research indicates that education about other species is not a requirement for recognition or categorization in non-human primates but it is in humans.