While the term "animal languages" is widely used, most researchers agree that they are not as complex or expressive as the human language. They argue that there are significant differences separating human language from animal communication even at its most complex, and that the underlying principles are not related.

Other researchers argue that an evolutionary continuum exists between the communication methods these animals use and human language. There is a general consensus that human language is more complex than communication between animals. For more on communication among non-human animals, see The Animal Communication Project. http://acp.eugraph.com

These are the properties of human language that are argued to separate it from animal communication:

• 'Arbitrariness:' There is no relationship between a sound or sign and its meaning.
• 'Cultural transmission:' Language is passed from one language user to the next, consciously or unconsciously.
• 'Discreteness:' Language is composed of discrete units that are used in combination to create meaning.
• 'Displacement:' Languages can be used to communicate ideas about things that are not in the immediate vicinity either spatially or temporally.
• 'Duality:' Language works on two levels at once, a surface level and a semantic (meaningful) level.
• 'Metalinguistics:' Ability to discuss language itself.
• 'Productivity:' A finite number of units can be used to create an infinite number of ideas.(some say this doesn't happen in human language)

Research with apes, such as the research Francine Patterson has done with Koko, suggests apes are capable of using language that meets some of these requirements. Koko's achievements were with a human language that she was taught, so her example only shows that apes are capable of using "language," but not that they are necessarily capable of inventing one on their own.

Arbitrariness has been noted in meerkat calls; bee dances show elements of spatial displacement; and cultural transmission has occurred with the offspring of many of the great apes who have been taught sign languages, the celebrated bonobos, Kanzi and Panbanisha, being examples. However, these single features alone do not qualify such instances of communication as being true language.

The most studied examples of animal languages are:

• Bee dance - used to comunicate direction of food source in many species of bees
• Bird songs - songbirds can be very articulate. African Grey Parrots are famous for their ability to mimic human language, and certain specimens can even understand basic commands.
• Whale songs - it is still a mystery what these very social and intelligent animals really communicate - although very different from the human languages, whale songs can not be easily dismissed as not being complex or expressive enough.