New Evidence That Orangutans and Gorillas Can Match Images Based On Biological Categories

Sep. 10, 2013 — The ability to form a general concept that connects what we know about the members of a category allows humans to respond appropriately when they encounter a novel member of that category. At an early age, children form categories to, for example, differentiate animals from inanimate objects and to differentiate dogs from cats. New research shows that other apes may form similar categories to represent different types of animals.

There are at least two ways to visually identify an animal as being similar to any other: the animals may be within a species and therefore closely resemble each other (so called 'perceptual' differences) or the animals may be considered to meet the criteria for a broader mental concept (for example, "reptiles do not have fur, they have short legs or have no legs, and lay eggs -- these all seem like reptiles"). Concept formation in human children has been subjected to extensive experimental study, with much focus on the interplay between concept acquisition and language acquisition. It has been proposed that these broader concepts depend upon formal scientific training and/or the ability to form verbal labels for such concepts. If non-human animals represent such concepts, this finding would be evidence against such a view. It is surprising then that the existence of natural categories, such as classification of animals, has not been extensively studied in language-less non-human apes. Studies of concepts in animals have instead paid close attention to the perceptual features that are used by the animals to extract information about category membership but have not typically allowed animals to demonstrate that they can also form concepts at different levels of breadth simultaneously.

In this study, a young female gorilla and four orangutans of various ages were shown images of animals and asked to match them to an image from the same species or family (i.e. one with a perceptual similarity). In an alternate experiment, they were presented with images of animals belonging to different taxonomic classes (insects, reptiles, fish, birds, and mammals) and were asked to match these images to sample images of other members of that class.

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