Is mental time travel what makes us human?

Barbara J. King

Michael C. Corballis 
THE RECURSIVE MIND 
The origins of human language, thought, and civilization 
291pp. Princeton University Press. £20.95 (US $29.95). 
978 0 691 14547 1

Published: 26 October 2011

Astonishing animals show up everywhere these days. Cooperative apes, grief-stricken elephants, empathetic cats and dogs crowd our bookshop shelves. It’s all the rage to plumb the cognitive and emotional depths of the animal world, rejecting sceptics’ sneers of “anthropomorphism” to insist that we’re finally coming to see animals for who they really are: not so different from us.

Pushing against this tide of animal awe is a competing cultural trope, the relentless seeking of human superiority. It’s from this second camp that Michael C. Corballis, a professor emeritus of psychology from New Zealand, has written The Recursive Mind: The origins of human language, thought, and civilization. Mental time travel and theory of mind, Corballis believes, are two uniquely human ways of thinking that propelled our species to heights above all others, thanks to what is called recursion.

The concept of recursion became an evolutionists’ darling largely on the heels of a paper written in 2002 by Marc Hauser, Tecumseh Fitch and Noam Chomsky. That paper, propelled to international notice by the participation of its famous third author, claimed that it’s a unique human trick to communicate by embedding structures within other structures, as when one noun phrase in a sentence is made to contain another. An example of such linguistic recursion is furnished by Corballis. The non-recursive sentences “Jane loves John” and “Jane flies aeroplanes” may be combined to produce the recursive sentence “Jane, who flies aeroplanes, loves John”. Less interested in language than the mind itself, Corballis states flatly that recursion is “the primary characteristic that distinguishes the human mind from that of other animals”.

Here is where mental time travel and theory of mind come in, because both are recursive ways of thinking. During mental time travel, an experience that we’ve had in the past or that we imagine for ourselves in the future is “inserted into [our] present consciousness”. Similarly, in theory of mind, we insert what we believe to be someone else’s state of mind into our own.

Corballis is right; we are indeed recursive thinkers. Day by day, if not hour by hour, our kind of animal may soar in memory-flight back in time, or imagine times far ahead. Picture a woman who stares at a summer evening’s starry sky, recalling the days long ago when her parents lovingly taught her the names of the constellations. She drifts into a reverie about the years ahead when her children may share star-learning sessions with her, and wonders if her daughter, already addicted to video games, will take to it as readily as her nature-delighted son.

Whether as elaborated as set forth in this hypothetical example or much simpler in content, the human mind’s recursive thinking makes us unique in the animal kingdom – or such is Corballis’s view. It’s a view only as valid as the accompanying comparative analysis of how other species think, and here Corballis falls short.

It is reasonable enough to note, as Corballis does, that recursion developed from “precursors identifiable in nonhuman species”. A distinctive quality, after all, can still be rooted in evolutionary antecedents (as religiosity may have deep roots in animal empathy). At one point, Corballis even allows that recursion “was not so much a new faculty as an extension of existing faculties”. But familiarity with the primary animal-behaviour literature leads to an alternative conclusion: some non-human animals are conscious selves who plan ahead and who carry out theory of mind thinking in a recursive way.

In 2009, writing in the journal Current Biology, Mathias Osvath described the actions of a male chimpanzee at a Swedish zoo in a way that made international news. In the morning, before visitors were allowed into the zoo, this animal would calmly pile up stones in small caches. He did this only in certain locations of his enclosure, facing the public area, and never when visitors were absent. Several hours after creating a cache, the chimpanzee hurled the stones in an aroused display aimed at the visitors. Osvath concluded that in accumulating the stones, the ape was planning for a future event (that is, the ape inserted an imagined future into its present consciousness).

Yet there is no need to hang the existence of recursion in chimpanzee thinking on a single ape living in captivity. Scientific reports of behaviour by wild chimpanzees include abundant instances of mental time travel and theory of mind. Consider the hunting behaviour described in The Chimpanzees of the Tai Forest by Christophe Boesch and Hedwige Boesch-Achermann (2000). In Ivory Coast, chimpanzees hunt colobus monkeys with true cooperation (rather than through fortuitous timing), and in a significant portion of cases they do so with anticipation. “The hunter”, Boesch and Boesch-Achermann write,

“not only has to anticipate the direction in which the prey will flee (recorded as a half anticipation), but also the speed of the prey so as to synchronize his movements to reach the correct height in the tree before the prey enters it (recorded as a full anticipation) . . . . We also recorded a double anticipation when a hunter not only anticipates the actions of the prey, but also the effect the action of other chimpanzees will have on the future movements of the colobus, that is he does not anticipate what he sees (the escaping colobus), but how a future chimpanzee tactic will further influence the escaping monkeys.”

Chimpanzee hunting skills in this arena develop gradually in individuals over a twenty-year period of learning. Boesch and Achermann-Boesch discuss these complex behaviours – as well as others, such as the chimpanzees’ calculated choice of attack strategies in intergroup encounters – in direct relationship to future planning and theory of mind.

And it is not only the big-brained apes who behave in this way. I wonder if, after viewing the documentary film A Murder of Crows, Corballis would still refuse to credit corvids – ravens and crows – with the recursive skills already outlined. In one striking scene, a New Caledonian crow (a bird admired by Corballis, though he thinks it incapable of recursive thinking) solves a complex experimental three-part tool-using problem, totally novel to this crow or any other. The bird thinks “three chess moves into the future”, as another observer has put it, by problem-solving to find one tool that is used to get another tool that then is finally used to procure food. It is an astonishing performance to watch.

Of course, humans are not crows – or chimpanzees. Scientists should indeed try to understand how the human lineage departed in the past from others and why. It’s greatly to Corballis’s credit that he rejects theories that purport to explain these events by heavy reliance on genetic mutations or innate brain modules in favour of some degree of mental continuity across species. Corballis even exhibits, now and again, slight unease at his own sharp distinction between the human and non-human. About theory of mind, he allows that “chimpanzees may indeed have some capacity to discern what other individuals can feel, see, and perhaps know”. But this is only “first-order” recursion, we are then informed – a surprise move given Corballis’s earlier claim that recursion is an absolute species boundary marker. To rescue the principle of human uniqueness, Corballis brings in “higher-order recursion”: we alone have “knowledge that another individual knows what I can see, know or feel, or even that the other knows that I know what she’s thinking”. This shift from recursion to higher-order recursion involves a sleight of hand and undermines the reader’s trust.

The situation is not helped by further inaccuracies. Corballis equates a “hunter-gatherer style of living” with “relatively undeveloped technologies”. Not necessarily so. Consider the site of Gobekli Tepe in ancient Turkey, a hilltop gathering centre and maybe the world’s first temple, constructed from monumental 50-ton blocks covered with animal carvings. This sophisticated structure was created by people with no settlements or domesticated animals or crops – that is, by hunter-gatherers.

Corballis assigns “the development of science and complex manufacture” to “the accomplishments of Western civilization”, “generally foreign to indigenous peoples”. The long distinguished history of science in the Muslim tradition – and much more besides – is crassly obliterated with this statement. Corballis refers to monkeys and mammals, and then cetaceans and mammals, though monkeys and cetaceans are of course mammals themselves. I cannot fathom the reason behind the statement, “If [wild chimpanzees] survive at all, it will probably be due only to the benevolence of humans”, especially given the logging and poaching horrors that Corballis himself mentions in the same paragraph.

Humanity’s recursive ways of thinking are more elaborate than those of other animals, but some other animals do think recursively as well. Can the degree of difference explain the origins of human thought, language and civilization? In order to chart a course through this territory, we will require a sharper navigator than Michael Corballis.

Barbara J. King is an anthropologist at the College of William and Mary. She is the author, most recently, of Being With Animals, 2010, and writes the Friday Animal Blog (www.barbarajking.com).