Animal intelligenceAnimal intelligence has been a controversial subject for a long time. Many have taken animal behaviour to be a series of unthinking mechanical responses to stimuli that originate in the animal's internal or external environments. In this view, complex behaviour can always be reduced to a configuration of reflexes where thought plays no role. It was assumed that only humans are capable of thought and only they have the capacity to learn language. Recent investigations of nonhuman animal intelligence not only contradict these ideas, but also present fascinating riddles. The debate over animal intelligence touches on many more fundamental debates on animal rights, human intelligence, artificial intelligence, and the degree to which empathy or abstract problem-solving or capacity for language should be involved in our idea of what is "intelligent". Some intelligence quotient tests have been used to estimate Great Ape intelligence as comparable to that of a human child. This has fuelled debates about Great Ape personhood. However, these and other specific claims regarding the intelligence of horses, dogs, cats, dolphins and whales in constant contact with human beings are generally discredited as being biased: in general the testers are also handlers, and care for the animals they test. Estimates of animal intelligence may be made based on construction of artifacts and tools by animals for food and other activities. The complexity of the communication process provides an estimate of the intelligence of the animal. Specific experiments have been designed to measure physiological correlates of thinking and symbolic communication, and examine deception and manipulation by animals. They are careful studies on the intelligence of pigeons. In these tests the bird must peck at a slide based on its contents that are related to the experimenter's hypothesis. It has been found that they can do tasks of generalization that are way beyond the capabilities of computers. The reasons for our concern with animal intelligence include the philosophical, ethical, and scientific. The philosophical question is related to the general question of other minds and how to define and quantify consciousness. The ethical significance of this research stems from the widespread belief that causing pain and suffering is morally wrong. If it were concluded that animals were persons like individuals, would we be able to slaughter them for food? The scientific importance is in our wish to explore all behavioral aspects of a specific animal.