Most behaviors do not occur in isolation, but rather are the result of interactions between members of a species or between members of different species. The topics of signaling and communication include behaviors from simple scent marking to complex courtship displays that involve multiple individuals. The distinction between signaling and communication is not entirely clear. Generally, signaling involves a stimulus that is not intended by the individual to send a message to a receiver, while communication is a deliberate act in which the exchange of information is mutually beneficial.
Some signals begin as behaviors with entirely different purposes but become exaggerated or ritualized as they become recognized for conferring information in a beneficial way. These signals are then acted on by natural selection to minimize risk to the signaler. A danger signal will become very exaggerated whereas cooperative signals will be minimized to reduce the conspicuousness of the signaler. Zahavi's handicap principle states that an honest signal must be costly to the signaler, meaning that only fit individuals can signal honestly. This principle is especially important in activities such as mate selection, in which finding a truly fit individual is extremely important. There are many types of signals, each with its own advantages and disadvantages. Among these are: chemical signaling, such as scent marking; visual signaling, which while limited to individuals in a direct line of site can be much more dynamic than other types of signaling; and acoustic signals, which are often among the most wide-reaching signals. Acoustic signals such as bird and whale songs have both genetically pre-determined and learned components and can be used to distinguish individuals or living groups.