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Communication refers to the transmission of information, and it is unsurprisingly ubiquitous amongst organisms, fulfilling many specific functions. An exchange of information can either occur between individuals of the same species (intraspecific) or members of different species (interspecific). When competing for resources such as food or territories, animals need to signal their superiority to rivals of the same species, while they demonstrate their suitability to potential mates in courtship. Animals also rely on communication to indicate a territory, the presence of a predator or the detection of a rich food source. Intraspecific communication is particularly important for co-operative hunting, a feeding strategy that is key to the success of lions and several species of canids, but has also evolved independently in some birds, fish and spiders. While the majority of communication is intraspecific, there are also numerous instances of communication between prey and its potential predator (e.g. mimicry, which represents an excellent example of evolutionary convergence in itself) or between the partners in a symbiosis.
When communicating with each other, animals can use a variety of signal types, either chemical, visual or vocal in nature. Each present remarkable examples of convergence. Chemical? Think of pheromones. Visual? Think of colour vision. Vocal? Think of song or ultrasound. Some animals, namely the electric fish (which are themselves convergent), have even evolved electrocommunication, where electrical signals can convey information about the sender's identity.
On the most basic level, cells communicate with each other via chemical signals. Signalling can occur within a multi-cellular organism but also between unicellular organisms, such as bacteria. Bacteria provide specific instances of convergence in terms of sociality and "intelligence", in which they show some striking similarities to eukaryotes. Another example of chemical communication is the pheromones, aerially wafted molecules that play a key role in the lives of many animals, notably the sexual life of insects such as moths. Not surprisingly this is a rich area of insights into evolutionary convergence because if an animal, such as a spider, can independently evolve the pheromone then a sexual lure is turned into a metaphorical honey trap. So too plants produce volatile substances to attract insects for pollination or just as ingeniously to attract parasitoid wasps that will attack caterpillars feeding on the plant.
Vocal communication can be found in many different groups of animals. The songs of birds are probably most loved by humans and also an excellent example of evolutionary convergence. Not only has song evolved three times independently within the birds, but there are also links to the songs of whales (notably humpback whales) and yes, music. In addition, some vocalisations of male mice show striking similarity to bird song but are at ultrasonic ranges and thus inaudible to us. The ability to communicate ultrasonically is rampantly convergent and occurs in other mammalian groups much more familiar than rodents, most famously in the bats but also cetaceans (whales and dolphins). Remarkably, ultrasonic communication has also evolved in one species of Chinese frog. At the other end of the frequency spectrum are very low frequency sounds that can travel over considerable distances, partly through air and partly through the ground as vibrations. The ability to detect and use such ground-borne sounds, referred to as seismic communication, has independently evolved in a number of animal groups, among them subterranean mammals, elephants, a few birds, some Puerto Rican frogs, insects and other arthropods (particularly spiders).
Although human language may be unique on earth, some elements of it can be found in animals as well. Some scientists would argue that this is true of the communication in the form of the highly complex dance of bees. Studies of dolphins, bonobos and perhaps African grey parrots indicate that they have converged on a level of cognitive complexity that enables them to understand a simple rule-based system of communication, and in some cases this includes elementary recognition of numbers. Bees, for example, can count to 4. The processes of vocal learning in young dolphins furthermore show interesting parallels to bird song and also human speech, including a "babbling" phase. These instances of convergence are particularly fascinating due to their complexity, whereas others are of interest because they are widely spread across very different organisms. One example of this is quorum sensing, a decision-making process used by groups and intensely studied in e.g. bacteria and social insects such as termites.