Laughter May Outlive Humans—and Even Numbers

Chimps and orangutans agree: Humor is truly fundamental.

By Jim Holt|Friday, June 27, 2008

Futurologists envision a world a million years from now in which the entire solar system has been turned into computronium and nanobots transform our garbage into foie gras. But in my experience, the repeated sin of futurologists is that they often extrapolate from what is new rather than from what is old. Computers and nanotechnology, impressive though they are, are things of relatively recent origin. As such, they are unlikely to be around for very long.

To find something that will pretty certainly endure into the distant future, we are obliged, paradoxically enough, to go back much farther into the past. And if we could cast a look back several million years, we would see, among other things, laughter and numbers. So we can be pretty confident that laughter and numbers will survive long after most of what we’re familiar with is gone.

The insight that old things tend to last and new things tend to disappear flows from the Copernican principle. This principle says, in essence, “You’re not special.” Before Copernicus, we imagined that we occupied a very special place at the center of the universe. Now we know better: We are on an average planet in an average galaxy in an average cluster. But the Copernican principle applies to time as well as to space. If there is nothing special about our perspective, we are unlikely to be observing any given thing at the very beginning or the very end of its existence. And that rather obvious point can lead to some interesting predictions.

Consider the longevity of the human race. If there is nothing special about the moment at which we observe our species, then it is 95 percent certain that we are seeing Homo sapiens in the middle 95 percent of its existence—not the first fortieth (2½ percent) or the last fortieth (2½ percent). Humans have already been around for about 200,000 years. That means we can, with 95 percent confidence, expect the species to endure for at least another 5,100 years (1/39 x 200,000) but for no more than 7.8 million years (39 x 200,000).

It was Richard Gott III, an astrophysicist at Princeton University, who pioneered this sort of reasoning. In a paper published in Nature on May 27, 1993, “Implications of the Copernican Principle for Our Future Prospects,” Gott noted that the Copernican-based calculation gives H. sapiens an expected total longevity comparable to that of other hominid species (H. erectus lasted 1.6 million years) and of mammal species in general (whose average span is 2 million years). It also gives us a decent shot at being around a million years from now.

What else might be around in the Year Million? Consider something of recent origin, like the Internet. The Internet has existed for about 25 years now (as I learned by going on the Internet and looking at Wikipedia). By Copernican reasoning, this means we can be 95 percent certain that it will continue to be around for another seven-plus months but that it will disappear within 975 years. So in the Year Million, there will almost certainly be nothing recognizable as the Internet. (This is, perhaps, not a terribly surprising conclusion.) Ditto for baseball. Ditto for what we call industrial technology, which, having come into existence a little more than two centuries ago, is likely to be superseded by something strange and new in the next 10,000 years.

Laughter and numbers, on the other hand, are good bets to survive a million years because they are two of the oldest things that are part of our lives today. How do we know this? Because we share both laughter and a sense of number with other species, and therefore with common ancestors that existed millions of years ago.

Take laughter. Chimpanzees laugh. Charles Darwin, in The Expression of the Emotions in Man and Animals, noted that “if a young chimpanzee be tickled—the armpits are particularly sensitive to tickling, as in the case of our children—a more decided chuckling or laughing sound is uttered; though the laughter is sometimes noiseless.” Actually, what primatologists call chimp laughter is more like a breathy pant. It is evoked not only by tickling but also by rough-and-tumble play, games of chasing, and mock attacks—just as with children prior to the emergence of verbal joking at age 5 or 6.

The human and chimpanzee lineages split off from each other between 5 million and 7 million years ago. On the reasonable assumption that chimp and human laughter are homologous rather than independently evolved traits, laughter must be at least 5 million to 7 million years old. (It is probably much older; orangutans also laugh, and their lineage diverged from ours about 14 million years ago.) So, by the Copernican principle, laughter is quite likely to be around in the Year Million.

Now take numbers. Chimps can do elementary arithmetic, and they have even been trained to use symbols like numerals to reason about quantity. But the sense of number is not confined to primates. Animals as diverse as salamanders, pigeons, raccoons, dolphins, and parrots have the ability to perceive and represent numbers. A few years ago, researchers at MIT discovered that macaque monkeys had specialized “number neurons” in the brain region that corresponds to the human number module. Evidently the number sense has an even longer evolutionary history than laughter. So again, by the Copernican principle, we can be quite certain that numbers will be around in the Year Million.

But what will our descendants’ mathematics look like? And what will make them laugh? The first question might seem the easier to answer. Mathematics, after all, is supposed to be the most universal aspect of human civilization, the part we assume would extend even to intelligent life elsewhere in the cosmos. In Carl Sagan’s science fiction novel Contact, aliens in the vicinity of the star Vega beam a series of prime numbers toward Earth. The book’s heroine, who works for SETI (Search for Extraterrestrial Intelligence), realizes with a frisson that the prime-number pulses her radio telescope is picking up must be generated by some form of intelligent life. But if the aliens beamed their jokes at us instead, we probably wouldn’t be able to distinguish them from the background noise. Indeed, sometimes we can barely distinguish the jokes in a Shakespeare play from the background noise. Just as nothing is more timeless than number, nothing is more parochial and ephemeral than humor, the core of laughter—or so we imagine. We are confident that a civilization a million years more advanced than our own would find our concept of number intelligible (and we, theirs), but our jokes would have them scratching their heads in puzzlement.

That is how we see matters at the moment. In the Year Million, though, I think the perspective will be precisely the reverse. Humor will be esteemed as the most universal aspect of culture. And number will have lost its transcendental reputation and be looked upon as a local artifact, like a computer operating system or an accounting scheme. If I am right, then SETI scientists should not be listening for primes but for something quite different.

Prime numbers—the numbers that can’t be split up into smaller factors and are thus the atoms of arithmetic—have an almost holy status today. What makes them seem transhuman to us now is their sheer orneriness. There are infinitely many of them, and they seem to crop up almost at random among the rest of the numbers. “There is no apparent reason why one number is prime and another not,” the mathematician Don Zagier declared in his inaugural lecture at Bonn University in 1975. “To the contrary, upon looking at these numbers, one has the feeling of being in the presence of one of the inexplicable secrets of creation.”

But the prime numbers are not really as transcendental as all that. They do obey a law. We just don’t grasp the law—yet. In 1859 the German mathematician Bernhard Riemann put forward what is now almost universally regarded as the greatest unsolved problem in mathematics: the Riemann hypothesis. This hypothesis holds the key to the primes’ true pattern, and once its truth or falsity is resolved, prime numbers will be rendered transparent to our understanding. How long must we wait? Mathematicians great and not so great have been trying to crack this nut ever since Riemann put it out there. “It will be another million years at least,” the late number theorist Paul Erdös pronounced, “before we understand the primes.”

The Copernican principle yields a rather different estimate. The Riemann conjecture has been open since it was first posed 149 years ago. That means we can be 95 percent certain that it will survive as an open problem for at least another four years or so (1/39 x 149) but that it will be dispatched within the next six millennia ?(39 x 149), well short of the Year Million. When it is solved, the prime numbers will finally be stripped of their cosmic otherness. We will realize that, like the rest of mathematics, they are man-made, a terrestrial artifact. They will seem about as trivial as a game of tic-tac-toe.

And how about laughter? Perhaps the best way to gauge future humor is to look at other primates: What do chimps find funny? The Central Washington University researcher Roger Fouts reported that Washoe, a chimpanzee who was taught sign language, once urinated on him while riding on his shoulders. The chimp snorted and made the sign for “funny.” Washoe was also observed playfully wielding a toothbrush as if it were a hairbrush. Moja, another of Fouts’s signing chimps, called a purse a “shoe” and wore it on her foot. A signing gorilla trained by another researcher appeared to derive amusement from offering rocks to people as “food.” Such supposed instances of simian humor (similar to the jokes of preschool children) involve the deliberate misnaming or misuse of things. They thus fit nicely under one of the three classic theories of humor, the incongruity theory, which holds that mirth results when two things normally kept in separate compartments of the mind are abruptly and surprisingly yanked together.

But why should the perception of incongruity cause a spasm of noisy chest-heaving? Laughter has long been viewed as a so-called luxury reflex, one that serves no obvious evolutionary purpose. In recent years, though, practitioners of the art of evolutionary psychology have been more imaginative in coming up with Darwinian rationales. One of the more seductive comes from the neuroscientist V. S. Ramachandran of the University of California at San Diego, who has advanced what might be called the false-alarm theory of laughter. A seemingly threatening situation presents itself; you go into fight-or-flight mode; the threat proves spurious; you alert your (genetically close-knit) social group to the absence of actual danger by emitting a stereotyped vocalization —one that is amplified as it passes contagiously from member to member.

Once the mechanism of laughter was set in place by evolution, the theory goes, it could be hijacked for other purposes: the expression of contempt for out-groups (as the superiority theory of humor claims) or the ventilation of forbidden sexual impulses (the relief theory of humor). But at the core of the original false-alarm mechanism of laughter is incongruity: the incongruity of a grave threat revealing itself to be trivial—­or, as the philosopher Immanuel Kant (an advocate of the incongruity theory) put it, “the sudden transformation of a strained expectation into nothing.” Incongruity is arguably the primeval kernel of laughter. And therefore, by the Copernican principle, it is likely to be the kernel of laughter in the Year Million.

That is why I think humor and mathematics will ultimately switch places, so to speak. The transcendence that numbers seem to possess arises from mere kinks in our local understanding, kinks that will eventually get straightened out. But the essence of humor is the dialectic between something and nothing, the most universal categories of all.

And what will jokes look like in the Year Million? We will laugh when incongruity is resolved in a clever way, when a strange-seeming something is exposed as a trivial nothing—when a proof of the Riemann hypothesis dissolves the Platonic otherness of the primes into obvious tautology, and what is today regarded as the hardest problem ever conceived by the human mind becomes a somewhat broad joke, fit for schoolchildren. We might laugh even harder at the thought that the end of the universe—its disappearance in a Big Crunch or expansion into dilute nothingness—itself has the logical form of a joke.

Adapted from Jim Holt’s essay, “The Laughter of Copernicus,” in Year Million: Science at the Far Edge of Knowledge, edited by Damien Broderick (Atlas and Company, $16). Holt is also the author of Stop Me If You’ve Heard This: A History and Philosophy of Jokes (W. W. Norton and Company).

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