How Animals Communicate
Among the surprises that have come from biology in the last few decades is the finding that animals so often communicate with each other. The discovery that so many species have a sort of language has been one of the intellectual set-backs that our “gut feeling” of superiority has suffered since Copernicus showed that the Earth is not the center of the solar system and Darwin revealed that our physical ancestors were rather like apes. Until quite recently it has been generally assumed that human language is unique, and certainly our power of communication greatly exceeds that of all other animals in complexity and versatility. But it now becomes clear that communication is a fundamental property of all living things. The discovery of the mechanism of inheritance by nucleic acids (DNA) has shown that every cell of every organism is controlled by the operations of what can only be called a set of instructions embodied in an elaborate code. Through every moment of our lives these instructions are read and copied by processes that are justly called transcription and translation, and so used by the cells to help them to perform their daily duties by making the correct new proteins. These discoveries have compelled biochemists to think about such unfamiliar matters as the nature of codes and languages, while linguists must come to realize that what they thought was unique to man is a universal property of life.
Some people would like to evade such uncomfortable thoughts by holding that when we speak of the genetic code we are only using a metaphor or analogy. But how else could the phenomena be described? What is involved is the need for a complete reassessment of the meaning we intend to convey when we speak of signs and languages. The American philosopher Peirce was the first in modern times to realize this problem clearly when in 1906 he founded the science of semiotics—the study of signs and symbols. He realized even then that symbolism is an essential element in all life—an assertion whose meaning must seem far from evident at first hearing. But the depth of his insight has become clear with the discovery that the nucleic acids function as stores of information, using an alphabet of four letters to form the sixty-four words whose combinations provide the language that controls all living things.
Since Peirce the science of semiotics has shown a mighty growth in many directions, some of them bedeviled by a very elaborate and arcane terminology. The students of signs have indulged in an orgy of inventing new ones. Fortunately zoosemiotics, the study of animal language, has managed to keep clear of the more esoteric flights of classification. Thomas Sebeok of Indiana University, though he coined the word zoosemiotics in 1963, has had the good sense to call his large new book simply How Animals Communicate. In it he brings together writers about the subject in every single group of animals from amoeba to man, and indeed from plants as well. For every flower communicates with animals—by color or scent. It may seem farfetched to call this communication. Do the plants then speak with a language? This is a good example of the unavoidable difficulties that face us as we come to recognize that none of our powers is unique, we are truly and completely part of the whole living world.
The criterion of communication is the inherited capacity to send messages by means of code signals either between the parts of an organism (as by nerves) or from one living thing to another. Plants certainly have evolved particular capacities to do this. Each species competes by the signals it sends for the favors of pollinators or of animals that can eat its fruits and disperse its seeds. There is often close adaptation of flower design and color to the vision of the pollinators. Flowers pollinated by humming birds are red, those visited by bees often blue, yellow, and ultraviolet, which they can see though it is outside our visible spectrum. Some species allow entry only of one type of insect, which is thus assured of a good food supply, while the plant gets the transfer of the pollen that it needs. Some species of orchid emit an odor that attracts only one species of bee. Some flowers mimic the appearance and even the odor of a female bee, so that the males pollinate the orchids by trying to copulate with them.
Of course it is important to restrict the term communication for a clear-cut class of behavior. As Colin Cherry has observed, telling a man to jump off a bridge is communication; pushing him is not. Where is the difference? Surely the criterion is in the use of a specialized system of symbols to achieve some end. Often the symbols are quite arbitrary, as are most of the words of human language. There is nothing eatable about the word “food.” In this sense the colors and scents of the plants are clearly symbols, not themselves part of pollination and dispersal of seeds but evolved as signals to help to achieve these ends.
Don Griffin of Harvard draws attention in this book to the many different ways in which animals communicate. The language of the bees was the first to be recognized by the Austrian zoologist Karl von Frisch in 1923. Some people have argued that this is not true communication because the bees cannot deny each other’s statements. But Martin Lindauer has recently shown that scout bees go out to search for possible sites for a new colony and when they return act in a way that constitutes an argument about which site is best.
Almost any feature of animal structure and behavior may be used for symbolic communication. Bees do it by dancing, ants by touching each other with the antennae, and butterflies by smell. Grasshoppers call to each other by sounds, and fireflies flash to find their mates. The females answer the flashes of the males and there are even examples where carnivorous fireflies lure others to death by misleading communications. The females of one sort answer males of other species by mimicking the sequence of flashes usually given by their females. So the male meets death instead of a mate.
Each medium of communication has its own advantages and defects. Visual signals are difficult to exchange in the dark and both they and sounds are generally only transitory. Few animals leave visual trails. Their more lasting signs are mostly chemical. Thus limpets leave their “homes” at high tide to feed and return along the trail they have laid. Chemical signals are not only long lasting but can also be carried for great distances by wind or water currents. Humans make little use of chemical signals, and we are apt to think of them as a crude and inexact medium of communication. Indeed they have been little studied until advances in analytical chemistry have shown what minute concentrations can be detected by some animals. It is calculated that one molecule of a stimulating substance falling on the antenna may be sufficient to activate a male butterfly to search for a female. On the other hand chemical signals lack directional specificity. The male must search for his mate by moving upwind.
Chemical signals that stimulate particular responses of attraction or aggression in others have been called pheromones, which is a fancy name for the smell by which all the neighborhood dogs are attracted to a bitch in heat. Again we are apt to consider such signals as beneath us, but they may play a larger part than we think in human likes and dislikes.
Electrical signaling is a means of communication for which we have no “natural” capacity at all. It is curious that it has become our main method of exchanging messages over long distances, even into space. All animals produce electric fields as part of the daily operations of their nerves and muscles. Yet only a few fish have the power to find their prey by electrical detection. Sharks are said to be able in this way to find flatfish buried in the sand. Many fish of different types make use of electricity produced by their muscles or nerves for communication by signals, which may be quite elaborate electric courtship songs indicating their sex and position to others of the same species. The very fact of the rarity of electric fish may make these signals especially valuable. They are also used by species that live in turbid rivers or lakes. A few fish such as the electric eel of South America emit shocks of hundreds of volts which stun their prey. Others send out repeated pulses and use the reflection of these to locate objects, a system of echolocation evolved millions of years before radar.
But sound is the medium that we think of first as the carrier of messages. Animals communicate by the type of noise most suited to their purposes. The type of sound that travels furthest varies according to the surroundings. The pure tones of birds in the woods that we find so pleasing have just that pitch that carries best among trees. The loud cawing of the crow carries for longer distances in open country. Many fish communicate by growls and grunts, which they produce by special muscles and receive through the resonance of the swim bladder, transmitted to the ear by a system of tiny bones rather like our own ear ossicles.
Water carries sounds five times faster than air and for great distances, and the whales make excellent use of this, as the essay by David and Melba Caldwell in Sebeok’s collection makes clear. Humpback whales can communicate over hundreds of miles. They use very lowpitched sounds, uttered at a particular depth in the ocean where there is a “deep sound channel” that traps the energy of the sound waves, which would be lost if they reached the surface or the floor of the sea. Contrary to popular belief whales do not use sounds to “talk,” in the sense of exchanging ideas by means of particular words. What their songs do is to provide general information to the group and to convey states of emotion. Yet among dolphins each animal has its own characteristic whistle or “signature,” which is after all a sort of word. The information that he sends can be translated as “Attention! I am a dolphin you know (or don’t know). I am on your left and I am excited.” One of the chief uses they make of sound is for location of other whales or of prey. Also, unlike humans, they apparently find interest in the rumblings of the bellies of others, using them as a guide to where to find food for themselves.
Birds seem to be the communicators par excellence, by their plumage, their display, and their song, but the amount of information they convey is not very great. It usually consists of identifying the singer, saying where he is and whether he has or has not the intention, say, to fly or to attack. Some birds use a sequence of songs in regular order, which has been compared to human grammar, but none of the sounds are differentiated into separate classes that can be combined in many ways like our nouns and verbs.
This is the feature that seems to separate human language from all other forms of communication. Nothing that has been found out about animals really helps very much to explain how we have come to have this wonderful power. Apes have indeed considerable capacity for signaling by sounds and facial expressions. These are used to organize their social, territorial, and sexual interactions, but not to provide even a minimum of detailed information to each other about the world. Chimpanzees such as the famous Washoe have shown great powers of learning to use a vocabulary of as many as 130 of the hand symbols of American Sign Language (“Ameslan”). The researches reported by Peter Marler and Richard Tenaza in this book demonstrate that they are able to combine these symbols in new ways, but not to understand new combinations shown to them, as a human child would do. These Ameslan experiments and those using operant training with colored plastic objects show that the capacity for learning symbolic associations is high in these apes. In a few cases the chimps made genuinely new constructions, as when Lucy biting into a radish referred to it as “cry hurt food” or Washoe when shown a Brazil nut signed “rock berry.” Sometimes what seemed to be mistakes turned out to be especially interesting. Thus Promack’s chimpanzee Sarah when offered an apple often gave the sign for a banana, not in error, but because that was what she wanted. This was held to show that she truly understood the significance of the arbitrary symbols.
One may ask why if apes have such powers they do not use them in nature. Perhaps indeed they do, but it may be that in their types of society our sort of symbolic communication would be of less value to them than their own signs. Those who work with these animals believe that they show us the rudiments of human speech, but probably most linguists and zoologists feel that this is a gap that we have not yet succeeded in closing. But this is not to say that it will continue to be impossible to do so. The findings of anthropologists show more clearly every year that our progress from the apes was gradual and this must surely have been true also of language.
In a fascinating article in this book Philip Lieberman shows how it is possible to reconstruct the probable type of speech possessed by manlike creatures such as Australopithecus, a million years ago. He argues that they could not have used the essential vowel sounds in the way that we do, but might have had simple speech based on a single vowel. If this suggestion can be developed it may carry us one step further toward knowing what sort of matters were first discussed by our ancestors. This might even lead to an understanding of how we came to our fundamental characteristics of thought—perhaps even why we feel so concerned to talk about our precious minds and consciousness. But the study of animal communication cannot quite do that for us—yet.
Do Animals Communicate? June 15, 1978