The trouble with language is its apparent altruism. Most speech, except for commands and questions, appears to transfer potentially useful information from speaker to listener. Speaking costs the speaker time and energy, and brings information benefits to the listener, so it looks altruistic. But, as we saw in the last chapter, evolution tends to avoid altruistic behavior.
Fifty years ago, altruistic communication did not seem such a problem. The animal behavior researcher Konrad Lorenz supposed that communication was for the good of the species. Animals could save their species lots of time and energy by evolving signals that reveal their intentions and motivations, especially in combat and courtship. This would reduce the deaths from combat and the confusions of courtship. Ritualized threats such as a dog's growling were supposed to convey accurate information about the dog's level of aggression and willingness to fight over a resource. If a growly dog meets a non-growly dog, the non-growly dog should back down, saving the species a wasteful dogfight. For several decades, the biologists' dogma was that animal signaling meant communication, communication revealed emotions and intentions, and communication evolved to make a species work more efficiently.
The rise of selfish-gene thinking in the 1970s shattered this idyllic view of animal signaling. Traits did not evolve for the good of the species. In their seminal 1978 paper, Richard Dawkins and John Krebs argued that animals should evolve to produce signals only when signaling gives them a net fitness benefit that helps their own genes replicate at the expense of other genes. Evolution cannot favor altruistic information-sharing any more than it can favor altruistic food-sharing. Therefore, most animals' signals must have evolved to manipulate the behavior of another animal for the signaler's own benefit. Dogs growl because it was easier for them to intimidate a rival than to fight. Smaller dogs could be intimidated by deep growls because a deep growler is probably a larger dog that would beat them in a fight anyway. Both the growl and the growl-sensitive ears evolved for selfish reasons.
The modern theory of animal signaling grew from this insight. Signals don't usually convey information about the world, because signalers have so many reasons to lie about the world. The theory suggests that animals usually evolve to ignore the signals from other animals that may be attempting to manipulate them. There are only a few exceptions. Predators listen to signals from prey that reliably say "You can't catch me," or "I'm poisonous." (Animals hiding from predators also evolve camouflage, the purpose of which is to hide signals of existence rather than to broadcast them.) Relatives listen to signals from other relatives that reliably say "Watch out for that predator!" Animals competing for a resource listen to signals that reliably say "I could kill you." And animals looking for a good mate listen to signals that say "I have good genes." Basically, that's it. Except for the warning signals about poison and predators, these signals are all fitness indicators. Any other kind of signal that evolved in nature would probably be pure manipulation, making the listener vulnerable to lies, sweet talk, and propaganda.
The handicap principle can make fitness indicators reliable. It can do so because the signal's cost is in the same currency—the currency of biological fitness—as the signal's information. This can work not only for fitness indicators that advertise good condition to potential mates, but for signals of desperation that advertise poor condition to relatives. For example, the handicap principle may also account for the effectiveness of a baby bird's gaping-mouth hunger display. Desperation signals also work with the currency of fitness: the animal reliably shows how much a desired resource would improve its fitness. Basically, fitness indicators advertise good condition and desperation indicators advertise poor condition. Signals between unrelated animals can convey information only about the signaler's own condition, broadly construed. There are no credible models showing that evolution can favor signals that carry any other kind of information, as long as there are incentives for deception.
This is a crippling problem for almost every existing theory of language evolution, but the problem is not widely understood. The handicap principle is not a magic wand that makes all communication truthful just because a speaker has paid a fitness cost. It cannot guarantee that a sentence conveys valid information. For example, just because someone accepted the pain and risk of infection necessary to get a tattoo does not make the tattoo's message valid. It just implies that the tattooed person is stoical and healthy.
Anthropologist Chris Knight has emphasized that human language is especially vulnerable to deception because it depends so much on "displaced reference"—referring to things that are distant in time or space. To a person dying of thirst, we can say, "There's a river over that hill." But displaced reference is hard to verify. We might be lying about the river, and the thirsty person might die if he goes over the hill expecting to reach a river and finds a desert instead. In fact, there are no theories of animal signaling in which reliable displaced reference could evolve, given significant conflicts of interest between signaler and receiver. Bee dances use displaced reference to indicate the direction and distance of food, but the bees are sisters from the same hive, so they have common interests. Between our Pleistocene ancestors there were always conflicts of interest, so it is very hard to see how reliable displaced reference could have evolved. If displaced reference was not reliable, listeners would not have bothered to listen, so speakers would not have bothered to speak.
This brings us back to the altruism problem. At first it sounds plausible to suggest that "language evolved to convey proposi-tional information from one mind to another." But that raises the
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