In The Phantom Tollbooth, Norton Juster’s classic, pun-filled adventure tale, the young Milo and his faithful companions unexpectedly find themselves transported to a bleak, mysterious island. Encountering a man in a tweed jacket and beanie, Milo asks him where they are. The man replies by asking if they know who he is—the man is, apparently, confused on the subject. Milo and his friends confer, then ask if he can describe himself.
“Yes, indeed,” the man replied happily. “I’m as tall as can be”—and he grew straight up until all that could be seen of him were his shoes and stockings—“and I’m as short as can be”—and he shrank down to the size of a pebble. “I’m as generous as can be,” he said, handing each of them a large red apple, “and I’m as selfish as can be,” he snarled, grabbing them back again.
In short order, the companions learn that the man is as strong as can be, weak as can be, smart as can be, stupid as can be, graceful as can be, clumsy as—you get the picture. “Is that any help to you?” he asks. Again, Milo and his friends confer, and realize that the answer is actually quite simple:
“Without a doubt,” Milo concluded brightly, “you must be Canby.”
“Of course, yes, of course,” the man shouted. “Why didn’t I think of that? I’m as happy as can be.”
With Canby, Juster presumably meant to mock a certain kind of babyish, uncommitted man-child. But I can’t help thinking of poor old Canby as exemplifying one of humankind’s greatest attributes: behavioral plasticity. The term was coined in 1890 by the pioneering psychologist William James, who defined it as “the possession of a structure weak enough to yield to an influence, but strong enough not to yield all at once.” Behavioral plasticity, a defining feature of Homo sapiens’ big brain, means that humans can change their habits; almost as a matter of course, people change careers, quit smoking or take up vegetarianism, convert to new religions, and migrate to distant lands where they must learn strange languages. This plasticity, this Canby-hood, is the hallmark of our transformation from anatomically modern Homo sapiens to behaviorally modern Homo sapiens—and the reason, perhaps, we were able to survive when Toba reconfigured the landscape.