Animal intelligence

The term animal intelligence is currently used in three distinct but overlapping ways:
 * as a synonym for animal cognition,
 * to refer to general or scientific discussion regarding relative differences of intelligence in different animal species
 * to pose the question “are animals intelligent?”

Cognition in animals
"Animal intelligence" may simply denote the study of cognition in animals. This was the earliest use of the term, and it is what George Romanes had in mind when he entitled a book Animal Intelligence. The modern name for this subject of study is animal cognition. Discussion of particular kinds of intelligence in animals can be found in that article or in articles linked from it.

Raising the question "Are animals intelligent?"
The phrase "animal intelligence" may introduce a discussion about whether it is meaningful to speak of animals as "intelligent" at all, or whether animal behaviour should instead be thought of as a series of unthinking mechanical responses to stimuli that originate in the animal's internal or external environments, with only humans being capable of conscious thought and flexible responding. This debate is now largely obsolete. On the one hand, it has been superseded by a more empirically-driven discussion about whether the research program of animal cognition, which assumes that animals have cognitive processes similar to those of humans, is or is not successful. On the other hand, it has been made obsolete by any of a number of more modern approaches to human intelligence. The radical behaviourists would see no place for cognition in the explanation even of human behaviour, while the study of artificial intelligence shows that much of what were once thought to be uniquely human mental capacities can be mimicked by an essentially mechanical system. Nonetheless, the question is unlikely to go away completely. The reasons for its persistence are philosophical and ethical as well as (perhaps more than) scientific. The philosophical question is the issue of the animal mind, which 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 conscious persons like human individuals, would we be able to slaughter them for food? And if so what makes cannibalism immoral?

Relative intelligence of different animal species
There are people who have viewed some animals as more intelligent than others: in European cultures, dogs, horses, great apes and (more recently) dolphins and parrots are seen as intelligent in ways that other animals are not. Crows have been attributed with humanlike intelligence by almost every culture that has encountered them. A number of recent survey studies have demonstrated the consistency of these rankings between people in a given culture. A common image is the scala naturae, the ladder of nature on which animals of different species occupy successively higher rungs, with humans typically at the top. Comparative psychologists have sought in vain for ways of providing an objective underpinning for these essentially subjective and anthropocentric judgements. Part of the difficulty is the lack of agreement about what we mean by intelligence even in humans (it obviously makes a big difference whether language is considered as essential for intelligence, for example). But in any case, different animals (including humans) seem to have different kinds of cognitive processes, which are better understood in terms of the ways in which they are cognitively adapted to their different ecological niches, than by positing any kind of hierarchy. One question that can be asked coherently is how far different species are intelligent in the same ways as humans are, i.e. are their cognitive processes similar to ours. Not surprisingly, our closest biological relatives, the great apes, tend to do best on such an assessment. It is less clear that the species traditionally held to be intelligent do unusually well against this standard, though among the birds, corvids and parrots typically are found to outperform other groups, and among the carnivores, dogs generally show better performance than cats. Despite ambitious claims, evidence of unusually high human-like intelligence among cetaceans is patchy, partly because the cost and difficulty of carrying out research with marine mammals mean that experiments frequently suffer from small sample sizes and inadequate controls and replication. Octopuses also exhibit many seemingly higher-level problem-solving skills.

List of animals considered 'intelligent'

 * Great apes (Humans, chimpanzees, gorillas, orangutans)
 * New World monkeys
 * Cetaceans (dolphins and whales)
 * Canines
 * Felines
 * Pigs
 * Octopuses
 * Corvids (ravens and crows)
 * Horses
 * Elephants
 * Parrots

Plant intelligence
Whether plants have intelligence in any sense humans can recognise is debatable; indeed, some victims of brain damage are often described as being in a 'persistive vegetative state'.