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Adapted from Why Is the Penis Shaped Like That? … And Other Reflections on Being Human, by Jesse Bering, by arrangement with Scientific American/Farrar, Straus and Giroux, LLC (North America), Transworld Ltd (UK), Jorge Zahara Editora Ltda (Brazil). Copyright © 2012 by Jesse Bering.
Once, while in a drowsy, altitude-induced delirium 35,000 feet somewhere over iceland, I groped mindlessly for the cozy blue blanket poking out beneath my seat, only to realize—to my unutterable horror—that I was in fact tugging soundly on a wriggling, sock-covered big toe. Now, with a temperament such as mine, life tends to be one awkward conversation after the next, so when I turned around, smiling, to apologize to the owner of this toe, my gaze was met by a very large man whose grunt suggested that he was having some difficulty in finding the humor in this incident.
Unpleasant, sure, but I now call this event serendipitous. As I rested my head back against that sanitation-paper-covered airline pillow, my midflight mind lit away to a much happier memory, one involving another big toe, yet this one belonging to a noticeably more good-humored animal than the one sitting behind me. This other toe—which felt every bit as much as its overstuffed human equivalent did, I should add—was attached to a 450-pound western lowland gorilla, with calcified gums, named King. When I was 20 and he was 27, I spent much of the summer of 1996 with my toothless friend King, listening to Frank Sinatra and the Three Tenors, playing chase from one side of his exhibit to the other, and tickling his toes. He'd lean back in his night house, stick out one huge ashen-gray foot through the bars of his cage and leave it dangling there in anticipation, erupting in shoulder-heaving guttural laughter as I'd grab hold of one of his toes and gently give it a palpable squeeze. He almost couldn't control himself when, one day, I leaned down to act as though I were going to bite on that plump digit. If you've never seen a gorilla in a fit of laughter, I'd recommend searching out such a sight before you pass from this world. It's something that would stir up cognitive dissonance in even the heartiest of creationists.
Do animals other than humans have a sense of humor? Perhaps in some ways, yes. But in other ways there are likely uniquely human properties to such emotions. Aside from anecdotes, we know very little about nonhuman primate laughter and humor, but some of the most significant findings to emerge in comparative science over the past decade have involved the unexpected discovery that rats—particularly juvenile rats—laugh. That's right: rats laugh. At least, that's the unflinching argument being made by researcher Jaak Panksepp, who published a remarkable, and rather heated, position paper on the subject in Behavioural Brain Research.
In particular, Panksepp's work has focused on “the possibility that our most commonly used animal subjects, laboratory rodents, may have social-joy type experiences during their playful activities and that an important communicative-affective component of that process, which invigorates social engagement, is a primordial form of laughter.” Now, before you go imagining some chortling along the lines of one rakish Stuart Little (or was he a mouse?), real rat laughter doesn't tend to sound very much like the human variety, which normally involves pulsating sound bursts starting with a vocalized inhalation and consisting of a series of short distinct saccades separated by almost equal time intervals. The stereotypical sound of human laughter is an aspirated h, followed by a vowel, usually a, and largely because of our larynx is rich in harmonics. In contrast, rat laughter comes in the form of high-frequency 50-kilohertz ultrasonic calls, or “chirps,” that are distinct from other vocal emissions in rats. Here's how Panksepp describes his discovery of the phenomenon: