<P> One theory to explain the evolution of traits like a peacock's tail is' runaway selection' . This requires two traits--a trait that exists, like the bright tail, and a prexisting bias in the female to select for that trait . Females prefer the more elaborate tails, and thus those males are able to mate successfully . Exploiting the psychology of the female, a positive feedback loop is enacted and the tail becomes bigger and brighter . Eventually, the evolution will level off because the survival costs to the male do not allow for the trait to be elaborated any further . Two theories exist to explain runaway selection . The first is the good genes hypothesis . This theory states that an elaborate display is an honest signal of fitness and truly is a better mate . The second is the handicap hypothesis . This explains that the peacock's tail is a handicap, requiring energy to keep and makes it more visible to predators . Thus, the signal is costly to maintain, and remains an honest indicator of the signaler's condition . Another assumption is that the signal is more costly for low quality males to produce than for higher quality males to produce . This is simply because the higher quality males have more energy reserves available to allocate to costly signaling . </P> <P> Ethologists and sociobiologists have characteristically analysed animal communication in terms of more or less automatic responses to stimuli, without raising the question of whether the animals concerned understand the meaning of the signals they emit and receive . That is a key question in animal cognition . There are some signalling systems that seem to demand a more advanced understanding . A much discussed example is the use of alarm calls by vervet monkeys . Robert Seyfarth and Dorothy Cheney showed that these animals emit different alarm calls in the presence of different predators (leopards, eagles, and snakes), and the monkeys that hear the calls respond appropriately--but that this ability develops over time, and also takes into account the experience of the individual emitting the call . Metacommunication, discussed above, also seems to require a more sophisticated cognitive process . </P> <P> It has been reported that bottlenose dolphins can recognize identity information from whistles even when otherwise stripped of the characteristics of the whistle; making dolphins the only animals other than humans that have been shown to transmit identity information independent of the caller's voice or location . The paper concludes that: </P> <P> The fact that signature whistle shape carries identity information independent from voice features presents the possibility to use these whistles as referential signals, either addressing individuals or referring to them, similar to the use of names in humans . Given the cognitive abilities of bottlenose dolphins, their vocal learning and copying skills, and their fission--fusion social structure, this possibility is an intriguing one that demands further investigation . </P>

Which animal whistles to communicate with its group