We humans like to think that we have capacities that make us not only distinct from all other creatures on the planet, but also superior to them. What other species, you might ask, has measured the speed of light, figured out how the universe began, invented the laptop computer, or painted a portrait? Our species has even succeeded in escaping from the planet altogether, even if only fleetingly. You might also ask, I suppose, why any other species would care to do these things, and we do need to be wary of our comfortable assumption that we are at the top of the earthly hierarchy, since it provides a too-easy justification of the appalling way we treat other animals. Let’s face it: We eat them, kill them for sport, drink their milk, wear their skins, ride on their backs, ridicule them, house them in zoos, and breed them to our own specifications.
By the same token, though, it cannot be denied that our species has dominated the earth like no other. Not only do we subjugate other creatures to our needs and whims, but we also mold the physical environment to our specifications, to the point that our success may prove to be our undoing. Unless we make better use of our vaunted intelligence, we run the risk of succumbing to pollution, global warming, or weapons of mass destruction—or, to think recursively, of weapons for the mass destruction of weapons of mass destruction. And yet we are biologically almost indistinguishable from the other great apes, and share a common ancestor with the chimpanzee and bonobo dating from only about six or seven million years ago—a mere eye-blink in evolutionary time. In marked contrast to human triumphalism, the great apes have been forced into ever-diminishing habitats, and they too are threatened with extinction.
Many have conjectured about why our species is so dominant on the planet. Assuredly, the reason is mental rather than physical—any number of animals out there can easily beat us in physical combat. Descartes argued that only humans are capable of free will. Aristotle suggested that man is the only political animal, and history suggests that he should have included women. Thomas Willis thought that only humans were capable of laughter, while Martin Luther argued that it was the possession of property that distinguished us. Benjamin Franklin attributed human uniqueness to tool-making, and the Greek philosopher Anaxagoras said it was the human hand that made us the wisest of species. Steven Mithen recently suggested that music may have started it all. Some years ago, in my book The Lopsided Ape, I argued that the asymmetry of the human brain was what made us what we are. There is probably some truth to at least some of these assertions, but readers may observe that lopsidedness receives very little mention in this book.
The one characteristic that has received most attention is language. “In the beginning,” said St. John, “was the Word, and the Word was with God, and the Word was God” (John 1:1). In the seventeenth century, René Descartes argued that language, as an expression of free will, was so unconstrained that it could not be explained in terms of mechanical principles, and must therefore have been a gift from God. In the following century, another French philosopher, Abbé Étienne Bonnot de Condillac, speculated about how language evolved, but as an ordained priest he was fearful of offending the church, and disguised his theory in the form of a fable—as we shall see in chapter 4. In 1866, the Linguistic Society of Paris banned all discussion of the origins of language.
In the twentieth century the linguist Noam Chomsky, himself a self-styled Cartesian, also argued that language could not have evolved through natural selection. His reasoning was based not on religion, but rather on a view of how language works. Basically, he argued that external language, as spoken or signed, must have arisen from an internal language—essentially the “language of thought”—that has no direct reference to the outside world, and so could not have been subjected to the pressures of adaptation to the environment. Chomsky therefore argued that internal language emerged from some single and singular event causing a rewiring, perhaps a fortuitous mutation, of the brain. He argued further that this event occurred late in the evolution of our species, perhaps even within the past 100,000 years. This account, although not driven by religious doctrine, does smack of the miraculous.
Chomsky is nevertheless one of the heroes of this book. He has long recognized the open-ended nature of language, and suggested that the key to this open-endedness is recursion. By applying principles in recursive fashion, we can create utterances, whether spoken or signed, of essentially infinite variability. Where I part from Chomsky, though, is in his view that thought itself is fundamentally linguistic. I argue instead that the modes of thought that made language possible were nonlinguistic, but were nonetheless possessed of recursive properties to which language adapted. Where Chomsky views thought through the lens of language, I prefer to view language through the lens of thought. This change of view provides the main stimulus for this book, since it not only leads to a better understanding of how we humans think, but it also leads to a radically different perspective on language itself, as well as on how it evolved.
I focus on two modes of thought that are recursive, and probably distinctively human. One is mental time travel, the ability to call past episodes to mind and also to imagine future episodes. This can be a recursive operation in that imagined episodes can be inserted into present consciousness, and imagined episodes can even be inserted into other imagined episodes. Mental time travel also blends into fiction, whereby we imagine events that have never occurred, or are not necessarily planned for the future. Imagined events can have all of the complexity and variability of language itself. Indeed I suggest that language emerged precisely to convey this complexity, so that we can share our memories, plans, and fictions.
The second aspect of thought is what has been called theory of mind, the ability to understand what is going on in the minds of others. This too is recursive. I may know not only what you are thinking, but I may also know that you know what I am thinking. As we shall see, most language, at least in the form of conversation, is utterly dependent on this capacity. No conversation is possible unless the participants share a common mind-set. Indeed, most conversation is fairly minimal, since the thread of conversation is largely assumed. I heard a student coming out of a lecture saying to her friend, “That was really cool.” She assumed, probably rightly, that her friend knew exactly what “that” was, and what she meant by “cool.”
That, then, is the theme of the book, but there are many excursions—into such questions as whether animals have language, whether human language evolved from manual gestures, whether all languages share common principles, why fiction is adaptive. Given the view that human thought and language evolved gradually, I sketch the likely evolution of our distinctive characteristics over the past 6 million or so years, and not, as Chomsky would have it, over the past 100,000 years. And if you don’t understand what recursion is, I hope this book will give you a better idea.
Many people have inspired my thinking scientifically and philosophically, and of course many of them, perhaps most of them, will disagree with at least some of my conclusions. They include Donna Rose Addis, John Andreae, Michael Arbib, Giovanni Berlucchi, Brian Boyd, Noam Chomsky, Nicola Clayton, Erica Cosentino, Karen Emmorey, Nicholas Evans, Francesco Ferretti, Tecumseh Fitch, Maurizio Gentilucci, Russell Gray, Nicholas Humphrey, Jim Hurford, Steven Pinker, Giacomo Rizzolatti, Michael Studdert-Kennedy, Thomas Suddendorf, Endel Tulving, and Faraneh Vargha-Khadem. I especially thank my wife, Barbara, for putting up with the hours I spent over the computer; at least she had her golf. My sons Tim and Paul—the latter claimed to a friend that he taught me everything I know—have often corrected me on points of psychology and philosophy.
I also owe a special debt of thanks to Eric Schwartz, Beth Clevenger, Richard Isomaki, and Jeffrey Weiss of Princeton University Press, and to my agent Peter Tallack, for their invaluable help in putting some shape into the book.