Communication
Language shapes human thinking and fosters complex cultures. There can be little doubt that language has played a critical role in human biological and cultural evolution. But communication is widespread among animals. Communication is achieved whenever a stimulus (the message) generated by one animal (the sender) has some behavioral influence on another animal (the receiver). Perhaps due to their active nature, animals seem to be prone to extract information from almost any stimulus. The preeminence of conununication is illustrated by cases in which senders have evolved traits that mask or enhance their presence. In
Figure 8.10 Addition in the chimpanzee Sheba. The setting included three locations that Sheba was trained to search before choosing a card. In the initial tests, two of the three locations had different numbers of oranges and the correct response was to point to the Arabic number that equaled the sum of oranges. In the situation represented in this figure, plastic cards with Arabic numbers replaced the oranges and Sheba was asked to add the numbers and point to the appropriate card. Sheba performed above chance in both tasks from the first session.
Source: Boysen and Berntson (1989); reproduced with permission from the American Psychological Association.
crypticity, animals that blend with the background minimize detection. For example, angler fish are sit-and-wait predators that catch prey by matching the appearance of an innocuous sponge. In aposematic coloration, animals advertise their presence by displaying bright colors and clear patterns. Caterpillars of the monarch butterfly Danaus plexippus feed on toxic substances that make them distasteful to predators, even as adult butterflies. Because predators (usually birds) tend to use vision to search for food, caterpillars have evolved bright colors to facilitate aversive learning by the predator. Predatory pressures are so intense that aposematic coloration tends to be convergent among unrelated species of insects, a phenomenon called Miillerian mimicry. Moreover, aposematic coloration occurs in species that are perfectly edible but benefit from predator avoidance, a phenomenon called Batesian mimicry.
In the previous examples, the message is conveyed by morphological traits, such as coloration. In other cases, the message is transmitted behaviorally. For example, Belding’s ground squirrels (Spermophilus beldingi), ringtailed lemurs (Lemur cattd), and vervet monkeys (Cer-copithecus aethiops) emit calls with different acoustic properties depending on the type of predator they detected. Such referential calls, like human spoken words, have specific meaning. Vervets have distinctive calls for leopards, eagles, and snakes, common predators in the Amboseli National Park of Kenya, where this behavior has been studied using call playbacks (Figure 8.11). Monkeys tended to move up a tree when hearing a playback of a “Leopard Call” but move down a tree when hearing an “Eagle Call.” A “Snake Call” induced a
Figure 8.11 Referential calls by vervet monkeys induced by different predators. The behavior of other monkeys is appropriate to the type of predator advertised by the call.
Source: Seyfarth, Cheney, and Marler (1980); reproduced with permission from Elsevier. Photo from Creative Commons, https://search.creativecommons.org, by richardrichard, license CC BY-ND 2.0.
looking-down behavior, and ifvervets were on the ground, they would adopt a bipedal posture while looking around them (Price, Wadewitz, Cheney, Seyfarth, Hammerschmidt, & Fischer, 2015).
Behavior is shaped by so many factors that its use to convey messages guarantees superior flexibility to that afforded by morphology. Flexible conununication is associated with complex social behavior by animals living in stable social groups and having evolved the capacity for social reinforcement. For example, chimpanzees engage in social interactions when solving problems and, at least in some locations, hunt CoIobus monkeys in groups. The degree of coordination required for effective group hunting suggests the presence of complex sets of signals.
Human language differs from these examples of conununication in the assembling of series of symbols within specific grammatical constraints. A person sending the same message that a vervet monkey produces with a single alarm call would say something like “There is a snake on your left!” Moreover, human language is less constrained by the situation in which it is used. In addition to alerting a friend about the snake, a similar interaction could occur later, when the two friends remember the episode. Such flexibility appears to be unique to human language. With these caveats in mind, let us consider whether nonhuman animals can acquire some of the properties of human language.
