Phantoms in the Brain: Probing the Mysteries of the Human Mind (36 page)

Twenty minutes later I heard an extremely loud, resounding "bang" and leapt out of bed. What was happening? A burglar perhaps? Naturally, with my limbic system activated, I "oriented," grabbed a flashlight and ran down the stairs. Nothing funny so far. Then, suddenly I noticed a large flower vase in pieces on the floor and a large tabby cat right next to it—the obvious culprit! In contrast to the airplane incident, this time I started laughing because I realized that the "anomaly" I had detected and the subsequent paradigm shift were of trivial consequence. All of the facts could now be explained in terms of the cat theory rather than the ominous burglar theory.

On the basis of this example, we can sharpen our definition of humor and laughter. When a person strolls along a garden path of expectation and there is a sudden twist at the end that entails a complete reinterpre−tation of the same facts
and
the new interpretation has trivial rather than terrifying implications, laughter ensues.

But why laughter? Why this explosive, repetitive sound? Freud's view that laughter discharges pent−up internal tension does not make much sense without recourse to an elaborate and far−fetched hydraulic 142

metaphor. He argued that water building up in a system of pipes will find its way out of the path of least resistance (the way a safety valve opens when too much pressure builds up in a system), and laughter might provide a similar safety valve to allow the escape of psychic energy (whatever that might mean). This "explanation" really doesn't work for me; it belongs to a class of explanations that Peter Medawar has called "analgesics" that "dull the ache of incomprehension without removing the cause."

To an ethologist, on the other hand, any stereotyped vocalization almost always implies that the organism is trying to
communicate
something to others in the social group. Now what might this be in the case of laughter? I suggest that the main purpose of laughter might be to allow the individual to alert others in the social group (usually kin) that the detected anomaly is trivial, nothing to worry about. The laughing person in effect announces her discovery that there has been a false alarm; that the rest of you chaps need not waste your precious energy and resources responding to a spurious threat.6 This also explains why laughter is so notoriously contagious, for the value of any such signal would be amplified as it spread through the social group.

This "false alarm theory" of humor may also explain slapstick. You watch a man—preferably one who is portly and self−important—walk down the street when suddenly he slips on a banana peel and falls down. If his head hit the pavement and his skull split open, you would not laugh as you saw blood spill out; you would rush to his aid or to the nearest telephone to call an ambulance. But if he got up casually, wiped the remains of the fruit from his face and continued walking, you would probably burst out laughing, thereby letting others standing nearby know that they need not rush to his aid. Of course, when watching Laurel and Hardy or Mr.

Bean, we are more willing to tolerate "real" harm or injury to the hapless victim because we are fully aware that it's only a movie.

Although this model accounts for the evolutionary origin of laughter, it by no means explains all the functions of humor among modern humans. Once the mechanism was in place, however, it could easily be exploited for other purposes. (This is common in evolution. Feathers evolved in birds originally to provide insulation but were later adapted for flying.) The ability to reinterpret events in the light of new information may have been refined through the generations to help people playfully juxtapose larger ideas or concepts—that is, to be creative. This capacity for seeing familiar ideas from novel vantage points (an essential element of humor) could be an antidote to conservative thinking and a catalyst to creativity. Laughter and humor may be a dress rehearsal for creativity, and if so, perhaps jokes, puns and other forms of humor should be introduced very early into our elementary schools as part of the formal curriculum.7

Although these suggestions may help explain the logical structure of humor, they do not explain why humor itself is sometimes used as a psychological defense mechanism. Is it a coincidence, for example, that a disproportionate number of jokes deal with potentially disturbing topics, such as death or sex? One possibility is that jokes are an attempt to trivialize genuinely disturbing anomalies by pretending they are of no consequence; you distract yourself from your anxiety by setting off your own false alarm mechanism. Thus a trait that evolved to appease others in a social group now becomes internalized to deal with truly stressful situations and may emerge as so−called nervous laughter. Thus even as mysterious a phenomenon as "nervous laughter" begins to make sense in the light of some of the evolutionary ideas discussed here.

The smile, too, may have similar evolutionary origins, as a "weaker" form of laughter. When one of your ancestral primates encountered another individual coming toward him from a distance, he may have initially bared his canines in a threatening grimace on the fair assumption that most strangers are potential enemies.

Upon recognizing the individual as "friend" or "kin," however, he might abort the grimace halfway, thereby producing a smile, which in turn may have evolved into a ritualized human greeting: "I know you pose no 143

threat and I reciprocate."8 Thus in my scheme, a smile is an
aborted
orienting response in the same way that laughter is.

The ideas we have explored so far help explain the biological functions and possible evolutionary origin of humor, laughter and smiling, but they still leave open the question of what the underlying neural mechanisms of laughter might be. What about Willy, who started giggling at his mother's funeral, and Ruth, who literally died laughing? Their strange behavior implies the existence of a laughter circuit found mainly in portions of the limbic system and its targets in the frontal lobes. Given the well−known role of the limbic system in producing an orienting response to a potenial threat or
alarm,
it is not altogether surprising, perhaps, that it is also involved in the aborted orienting reaction in response to a
false alarm
—laughter. Some parts of this circuit handle emotions—the feeling of merriment that accompanies laughter—whereas other parts are involved in the physical act itself, but at present we do not know which parts are doing what.

There is, however, another curious neurological disorder, called pain asymbolia, which offers additional hints about the neurological structures underlying laughter. Patients with this condition do not register pain when they are deliberately jabbed in the finger with a sharp needle. Instead of saying, "Ouch!" they say,

"Doctor, I can feel the pain but it doesn't hurt." Apparently they do not experience the aversive emotional impact of pain. And, mysteriously, I have noticed that many of them actually start giggling, as if they were being tickled and not stabbed. For instance, in a hospital in Madras, India, I recently examined a schoolteacher who told me that a pinprick I administered as part of a routine neurology workup felt incredibly funny—although she couldn't explain why.

I became interested in pain asymbolia mainly because it provides additional support for the evolutionary theory of laughter that I've proposed in this chapter. The syndrome is often seen when there is damage to a structure called the insular cortex—buried in the fold between the parietal and temporal lobes (and closely linked to the structures that were damaged in Willy and Ruth). This structure receives sensory input, including pain from the skin and internal organs, and sends its output to parts of the limbic system (such as the cingulate gyrus) so that one begins to experience the strong aversive reaction—the agony—of pain. Now imagine what would happen if the damage were to disconnect the insular cortex from the cingulate gyrus. One part of the person's brain (the insular cortex) tells him, "Here is something painful, a potential threat," while another part (the cingulate gyrus of the limbic system) says a fraction of a second later, "Oh, don't worry; this is no threat after all." Thus the two key ingredients—threat followed by deflation—are present, and the only way for the patient to resolve the paradox is to laugh, just as my theory would predict.

The same line of reasoning may help explain why people laugh when tickled.9 You approach a child, hand stretched out menacingly. The child wonders, "Will he hurt me or shake me or poke me?" But no, your fingers make light, intermittent contact with her belly. Again, the recipe—threat followed by deflation—is present and the child laughs, as if to inform other children, "He doesn't mean harm. He's only playing!" This, by the way, may help children practice the kind of mental play required for adult humor. In other words, what we call "sophisticated cognitive" humor has the same logical form as tickling and therefore piggybacks on the same neural circuits—the "threatening but harmless" detector that involves the insular cortex, cingulate gyrus and other parts of the limbic system. Such co−opting of mechanisms is the rule rather than the exception in the evolution of mental and physical traits (al−

though in this case, the co−opting occurs for a related, higher−level function rather than for a completely different function).

These ideas have some bearing on a heated debate that has been going on among evolutionary biologists in general and evolutionary psychologists in particular during the last ten years. I get the impression that there are two warring camps. One camp implies (with disclaimers) that every one of our mental traits—or at least 144

99 percent of them—is specifically selected for by natural selection. The other camp, represented by Stephen Jay Gould, calls members of the first camp "ultra−Darwinists" and argues that other factors must be kept in mind. (Some of the factors pertain to the actual selection process itself and others to the raw material that natural selection can act on. They complement rather than contradict the idea of natural selection.) Every biologist I know has strong views on what these factors might be. Here are some of my favorite examples:

• What you now observe may be a bonus or useful by−product of something else that was selected for a completely different purpose. For example, a nose evolved for smelling and warming and moistening air but can also be used for wearing spectacles. Hands evolved for grasping branches but can now be used for counting as well.

• A trait may represent a further refinement (through natural selection) of another trait that was originally selected for a completely different purpose. Feathers evolved from reptilian scales to keep birds warm but have since been co−opted and transformed into wing feathers for flying; this is called preadaptation.

• Natural selection can only select from what is available, and what is available is often a very limited repertoire, constrained by the organism's previous evolutionary history as well as certain developmental pathways that either are permanently closed or remain open.

I'd be very surprised if these three statements were not true to some extent regarding the many mental traits that constitute human nature. Indeed, there are many other principles of this sort (including plain old Lady Luck or contingency) that are not covered by the phrase "natural selection."10 Yet ultra−Darwinists steadfastly adhere to the view that almost all traits, other than those obviously learned, are specific products of natural selection. For them, preadaptation, contingency and the like play only a minor role in evolution; they are

"exceptions that prove the rule." Moreover, they believe that you can in principle reverse engineer various human mental traits by looking at environmental and social constraints. ("Reverse engineering" is the idea that you can best understand how something works by asking what environmental challenge it evolved
for.
And then, working backward, you consider plausible solutions to that challenge. It is an idea that is popular, not surprisingly, with engineers and computer programmers.) As a biologist, I am inclined to go with Gould; I believe that natural selection is certainly the single most important driving force of evolution, but I also believe that each case needs to be examined individually. In other words, it is an empirical question whether some mental or physical trait that you observe in an animal or person was selected for by natural selection. Furthermore, there are dozens of ways to solve an environmental problem, and unless you know the evolutionary history, taxonomy and paleontology of the animal you are looking at, you cannot figure out the exact route taken by a particular trait (like feathers, laughter or hearing) as it evolved into its present form.

This is technically referred to as the "trajectory" taken by the trait "through the fitness landscape."

My favorite example of this phenomenon involves the three little bones in our middle ear—the malleus, incus and stapes. Now used for hearing, two of these bones (the malleus and incus) were originally part of the lower jaw of our reptilian ancestors, who used them for chewing. Reptiles needed flexible, multielement, multihinged jaws so they could swallow giant prey, whereas mammals preferred a single strong bone (the dentary) for cracking nuts and chewing tough substances like grains. So as reptiles evolved into mammals, two of the jawbones were co−opted into the middle ear and used for amplifying sounds (partly because early mammals were nocturnal and relied largely on hearing for survival). This is such an ad hoc, bizarre solution that unless you know your comparative anatomy well or discovered fossil intermediates, you never could have deduced it from simply considering the functional needs of the organism. Contrary to the ultra−Darwinist view, reverse engineering doesn't always work in biology for the simple reason that God is not an engineer; he's a hacker.

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What has all this got to do with human traits like smiling? Everything. If my argument concerning the smile is correct, then even though it evolved through natural selection, not
every
feature of a smile is adaptive for its current demand. That is, the smile takes the particular form that it does not because of natural selection alone but because it evolved from
the very opposite
—the threat grimace! There is no way you could deduce this through reverse engineering (or figure out its particular trajectory through the fitness landscape) unless you also know about the existence of canine teeth, knew that nonhuman primates bare their canines as a mock threat or knew that mock threats in turn evolved from real threat displays. (Big canines are genuinely dangerous.)