The Recurring Question - Human Evolution

The Recursive Mind: The Origins of Human Language, Thought, and Civilization - Michael C. Corballis 2014


The Recurring Question
Human Evolution

Whether or not recursion holds the key to the human mind, the question remains how we came to be the way we are—at once so dominant over the other apes in terms of behavior and yet so similar in genetic terms. In chapter 10, I set the problem in terms of the classic debate between Cartesian discontinuity and Darwinian continuity, and then consider some of the steps that made us the way we are. In modern-day science, it is difficult to avoid the conclusion that the human mind evolved through natural selection, although as we have seen, some recent authors, including Chomsky, still appeal to events that smack of the miraculous—a mutation, perhaps, that suddenly created the capacity for grammatical language. This is the “big bang” theory of language evolution, referred to in chapter 4. But of course we do have to deal with the seemingly vast psychological distance between ourselves and our closest relatives, the chimpanzees and bonobos.

In chapter 11 I consider the possible steps by which we became human. The most critical period was probably the Pleistocene, dating from some 2.6 million years ago until around 12,000 years ago. Evolutionary psychologists have supposed that this was the epoch during which the human mind took shape, largely as a consequence of the shift from an arboreal existence to a more terrestrial existence as hunter-gatherers. But as I explain, we were lucky to make it through, since of the 20 or so hominin species so far identified through fossil remains, only one remains.

That species is Homo sapiens, who emerged in Africa late in the Pleistocene, some time within the past 200,000 years. That species seems to have been endowed with sufficient qualities to ensure survival, and this is the topic of chapter 12. Some have argued that it was language that made all the difference, as though we talked the Neandertals out of existence, but this view is not in keeping with the Darwinian assumptions of this book. In chapter 12 I suggest that it was not language itself that made the difference. Now read on.

The Recurring Question

What a piece of work is a man! how noble in reason! how infinite in faculty! in form and moving how express and admirable! in action how like an angel! in apprehension how like a god! the beauty of the world! the paragon of animals!

—Shakespeare’s Hamlet II.2

So spoke Hamlet. Admiration of our own species is certainly one of our characteristics, although not all authors have been so fulsome. Blaise Pascal, the seventeenth-century French mathematician, had a more jaundiced view:

What a chimera, then, is man! what a novelty, what a monster, what a chaos, what a subject of contradiction, what a prodigy! A judge of all things, feeble worm of the earth, depositary of the truth, cloaca of uncertainty and error, the glory and the shame of the universe!1

Glory or shame, we cannot but marvel at our human achievements, although they may ultimately strangle us into extinction on our hitherto benevolent planet. The variety and ingenuity of human invention seemingly knows no bounds, ranging from jelly beans to jumbo jets, hamburgers to Hamlet, spears to space probes, internal combustion to the Internet, Beethoven to the Beatles—and cell phones.

All of this is in marked contrast to the exploits of our nearest relatives, the African apes, who are restricted to ever more confined regions of Africa, in conditions that by human standards are starkly primitive. If they survive at all, it will probably be due only to the benevolence of humans, and that certainly cannot be guaranteed. The forests of West Africa are the last stronghold of the African apes in the wild, but mechanized logging means that the numbers of apes (gorillas and chimpanzees) fell by more than half between 1983 and 2002, and there is no end in sight—no end to logging, that is, since the end of the line for the wild chimpanzee seems all too clearly in view. To compound the problem, ebola haemorrhagic fever continues to run unchecked through the chimpanzee population, and hunting for so-called bushmeat has changed from a subsistence activity to a commercial enterprise with the rise of forestry.2 And yet we share a common ancestry with chimpanzees that goes back only about six or seven million years—an eyeblink on the evolutionary time-scale—and their genetic makeup is something over 98 percent identical to our own.

It is no wonder then that we humans have been tempted to bestow on ourselves some extra quality, perhaps of a nonmaterial sort, that allows us to rise above our ape cousins, closer to angels than to apes. Here is how the Eighth Psalm put it:

What is man, that thou art mindful of him …? For thou hast made him a little lower than the angels, and has crowned him with glory and honour. Thou hast made him to have dominion over the works of thy hands; Thou hast put all things under his feet; All sheep and oxen, yea, and the beasts of the field; The fowl of the air, and the fish of the sea.

Yea indeed. By hovering between ape and angel, we can then indulge in self-glorification for our elevation above the animals, or in self-flagellation for our inability to achieve sainthood, an uneasy equilibrium exploited by religious authorities. In Paradise Lost, John Milton wrote:

The mind is its own place, and in itself

Can make a Heav’n of Hell, and a Hell of Heav’n.

But even if the path to heaven is an arduous one, are we really justified in supposing that our minds have somehow managed to transcend the physical laws of the universe?

Descartes’s Legacy

The idea that we might be possessed of a spiritual transcendence was given scientific and religious respectability by René Descartes, sometimes considered the founder of modern philosophy. He was intrigued by mechanical toys, popular at the time, and this led him to wonder whether animals might be reduced to mere machines, whose behaviors could be explained by mechanical principles. He argued that this was indeed true of animals, and for the most part of humans as well, at least with respect to bodily functions and reflexive behavior.

But we humans were unique, he thought, in possessing a flexibility of thought and action that could not be reduced to mechanical principles. This was most evident in language, whose unboundedness defied any attempt to reduce it to deterministic laws, but more generally in free will. We seem to be able to choose what action to take independently of the forces around us. Descartes argued that these freedoms must have arisen from some nonphysical influence that entered the brain through the pineal gland, an organ conveniently located near the middle of the brain so that the incoming signals could be most effectively distributed. That influence could be attributed to God. Because it allowed for free will, it also gave us the opportunity to sin.

Descartes’s happy compromise established what is known as mind-body dualism, in which the nonmaterial influence that we call mind is separate from the mechanical influences that govern the body, and indeed much of the brain. This was a smart move by Descartes, since it allowed for both the continuation of religion and the development of neuroscience. Yet there is some doubt about whether Descartes was entirely objective in his views, or whether he was simply anxious not to offend the church. Certainly, there were those who disagreed with him. Perhaps the most notable of these was Princess Elizabeth of Palatine, granddaughter of James I of England and niece of Charles I, who challenged the idea that the human mind did not operate according to mechanical laws. Elizabeth, a devout but tolerant Calvinist, maintained a friendly correspondence with Descartes, but would not allow her letters to him to be published at the time. More than 200 years later her letters were found, and they were eventually published in 1879.

Whatever Elizabeth thought, I suspect that today most people, even in nontraditional societies with no knowledge of Western philosophical thought, would agree with Descartes. Somehow, we don’t feel as though we are mere machines. We may well believe that animals are, and this belief may make us feel more comfortable about slaughtering animals for food, or exploiting them for labor or amusement—although we may draw the line at some species, such as family pets, and we may see in the soulful eyes of the chimpanzee a close kindred spirit. In the Spectator onetime editor Frank Johnson complained of “boffins” who would reduce humans to robots, proudly declaring his belief in an immortal soul. “Human beings,” he wrote, “will always top the earthly hierarchy.”3

Johnson probably echoes a widespread reluctance to believe that the mind can be reduced to a machine, despite the extraordinary progress of neuroscience and ubiquitous pizza-like images of activity in the brain corresponding to our thoughts and emotions. In the last week of February 2004, the Reader’s Digest published a survey which revealed that eight out of 10 Australians believe that some people possess psychic powers, and seven out of 10 believe in the afterlife. A majority of people also believe that it is possible to communicate with the dead, and that extraterrestrials have visited the planet. In that same week, Americans voted Australia to be the country with the best image on the planet.4

But we shouldn’t single out the Australians, since similar statistics could no doubt be compiled from most other societies. One survey shows that about 90 percent of people in the United States believe in God, about 70 percent believe in heaven and the afterlife, and about 58 percent believe in hell.5 Indeed, a prominent cognitive scientist at Yale University, Paul Bloom, has argued in his recent book Descartes’ Baby that dualism itself is innate.6 We have, in other words, a natural-born disposition to believe that mind and body are distinct. Of course, this is not to say that they are distinct, but simply that we have been born with the instinct to believe them so. If dualism is wired into our brains, no wonder we have such difficulty accepting a mechanistic view of ourselves. It is an ironic thought, though, that the mechanical functioning of the brain might be what causes it to believe that it is not mechanical.

We should also not judge religion too harshly, since there are sound reasons to suppose that religious belief may itself have been a product of natural selection—not directly, perhaps, but as a consequence of selection for the survival of groups. We humans are fundamentally social creatures, and religion provided one mechanisms for ensuring group cohesion. Religion does pose problems for the theory of evolution, as we shall see below, and the ultimate irony may be that the explanation for religion lies in evolution itself.

Darwin’s Heresy

Although Descartes’ dualism had had its critics, the most serious challenge came from Darwin’s theory of evolution by natural selection, which recognizes no fundamental difference between humans and other species. Not surprisingly, there was antagonism from religious and educational authorities, which continues to this day, a century and a half after the publication of On the Origin of Species by Means of Natural Selection. Not for nothing has evolution been dubbed “Darwin’s dangerous idea.”7 Darwin himself delayed publication of his book because he knew it would cause trouble. He had been warned, in fact, by the opprobrium that greeted an earlier anonymous publication entitled Vestiges of the Natural History of Creation, published in 1844, which dared to suggest that humans might have evolved from primates without divine intervention. Darwin was eventually persuaded to publish only because Alfred Russel Wallace had independently reached similar conclusions, and might publish before he did. Although Darwin had little to say on human evolution until his 1871 book, The Descent of Man, the implications were clear. As he correctly surmised, we are descended from the African apes, and we now know with reasonable certainty that we share a common ancestor with the chimpanzee dating from around six or seven million years ago.

Darwin’s theory of natural selection is one of the truly major insights in the history of science. The eminent biologist Theodosius Dobzhansky famously wrote that “nothing in biology makes sense except in the light of evolution,”8 and Darwinian theory is almost universally accepted among biologists, although they may quibble about some of the details. Nevertheless it continues to cause controversy and opposition, especially in parts of the United States. Early in 2004 it was noted that the proposed curriculum in science and math drafted by the Georgia State Board of Education does not include the word “evolution,” to the consternation of scientists.9 There has been persistent pressure, especially in the United States, to introduce an alternative to Darwinian evolutionary theory known as “intelligent design,” which is thinly disguised religious doctrine dressed up to look like science.10

Intelligent design is explained in an increasingly influential book called Of Pandas and People, by Percival Davis and Dean Kenyon. As of August 2005 this book, then in its fifth edition, had sold more than 20,000 copies.11 Davis and Kenyon write: “Intelligent design means that various forms of life began abruptly through an intelligent agency, with their distinctive features already intact—fish with fins and scales, birds with feathers, beaks and wings, etc.”12 A classic case is the eye, said to be too complex to have evolved incrementally through natural selection. Actually, the eye is not an outstanding example of design, since the retina is installed back to front, and light has to filter through a network of nerve fibers before it reaches the light-sensitive rods and cones, and as a consequence there is a “blind spot” where these fibers gather to leave the eyeball in the optic nerve. It makes you itch to take the thing apart and redesign it.13

But it is of course human evolution with which advocates of intelligent design are most concerned. We are so advanced relative to other animals, the argument goes, that we could not possibly have made the journey millimeter by millimeter, through the selection of incremental changes that proved adaptive. Darwinian theory is caricatured as implying that the human condition is the result of random variation, as plausible as the possibility that an ape, given a typewriter, might adventitiously produce the plays of Shakespeare. Of course the theory of natural selection does depend on random variation, but selection of those variations that lead to increased biological fitness leads to systematic progression toward more adaptive forms. The trick is that evolution is a cumulative process, leading incrementally and inexorably toward greater fitness. One end product was a Shakespeare who did write all those plays.14 The real problem with intelligent design, though, is that it needs an intelligent designer, and its advocates provide no information on where that designer is to be found, or how to approach her to fix up that little problem with the eye. Merely to postulate an all-knowing, all-encompassing intelligent designer is bad science, since it does not explain anything, and there seems no way to refute it.

Not all religions accept intelligent design. Writing in the 18 January 2005 issue of L’Osservatore Romano, the official Vatican paper, Fiorenzo Facchini argued that intelligent design belongs to the realms of philosophy and religion, but not of science. He stated that “it is not correct from a methodological point of view to stray away from the field of science while pretending to do science.” The Vatican has for many years tolerated the teaching of evolutionary theories, and in 1950 a papal encyclical officially permitted Catholics to discuss Darwin’s theory of evolution. In another development, on 20 December 2005 federal district court judge John Jones III ordered the schools in Dover, Pennsylvania, to remove references to intelligent design from the science curriculum, on the grounds that it is not science.

Part of the reason for resisting Darwinian theory is that it seems to dislodge humans from the pedestal of superiority. We should not be too complacent, though. Human society is witness to extraordinary accomplishments, but most individual humans have little understanding of the miracles that surround them. Most of us would be utterly helpless if transported back to the African savanna of a million years ago. Without matches, we would probably have difficulty lighting a fire to keep predators at bay, let alone constructing a helicopter to get us out of there. There are probably only a handful of people who really understand the general theory of relativity, or the recent proof of Fermat’s last theorem. Alfred Russel Wallace, Darwin’s rival, was so taken with the difference between educated Europeans and primitive “savages” that he was prompted to invoke divine intervention to explain the difference—he wrote that “natural evolution could only have endowed the savage with a brain a little superior to that of an ape.”15 Darwin himself was appalled, and wrote to Wallace, “I hope you have not murdered too completely your own child and mine.”16

In contrast to the theory of intelligent design, the theory of evolution by natural selection is genuine science in that it is open to refutation, as Darwin himself realized. In the sixth edition of The Origin of Species, published in 1872, he wrote: “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.” Descartes had suggested the pineal gland as the organ that might account for human uniqueness, but this turned out to be without foundation, although some parapsychologists still believe that it may be responsible for telepathy and other extrasensory powers. The nineteenth-century anatomist Richard Owen maintained that a brain structure known as the hippocampus minor was unique to humans, but Darwin’s friend and protagonist Thomas Henry Huxley disproved this by showing that all apes possess this structure. The role of the hippocampus minor was ridiculed, albeit in a befuddled way, by Charles Kingsley in his 1886 book The Water Babies:

You may think that there are other more important differences between you and an ape, such as being able to speak, and make machines, and know right from wrong, and say your prayers, and other little matters of that kind; but that is a child’s fancy, my dear. Nothing is to be depended on but the great hippopotamus test.

But what exactly is the hippocampus minor? Neuroscientists are familiar with the hippocampus, a structure in the brain that plays an important role in memory, and others may identify the hippocampus with that lovely undulating creature, the sea horse, whose feminist principles have ensured that it is the male who carries the unborn young. In the nineteenth century, the hippocampus minor was identified as a ridge in the floor of the rearward horn of the lateral ventricle, and was clearly distinguished from the hippocampus itself, then called the hippocampus major. Owen’s idea that the hippocampus minor might be important probably owes something to the famed second-century anatomist Galen, who thought that the faculties of the mind resided not in the matter of the brain itself, but rather in the ventricles, which are the fluid-filled spaces in the brain. In any event, after the spat between Owen and Huxley, the term “hippocampus minor” disappeared, and was replaced by its original name, “calcar avis,” meaning cock’s spur. It now lives only in the most obscure corners of anatomy texts, and probably doesn’t do much for us at all.17

Of course if we do discover some complex organ that exists in humans but is not present in the other apes, this would indeed pose problems for Darwinian theory. Such a discovery seems unlikely. There can no longer be any serious doubt that we share our most recent common ancestry with the chimpanzee and bonobo, and slightly earlier ancestry with other great apes. Going further back we share ancestry, albeit ever diminishing, with monkeys, mammals, and ultimately all living creatures. Indeed molecular analysis tells us that we are biologically closer to the chimpanzee than the chimp is to the gorilla, outward appearances notwithstanding. Any uniqueness we may claim has come about, not through the magical insertion of some new organ, or through divine intervention, but rather through evolutionary tinkering. This no doubt involved the modification of growth patterns, and the handy trick of using organs that evolved for one purpose to achieve quite different ends. Just as the nose was modified to become the elephant’s trunk, and the forelimbs to become the wings of birds, so nature has taken the body and brain of an ape and turned it into a human. Just another ape, really, albeit one with some interesting properties.

Many of those properties have to do with what we are pleased to call mind. It is sometimes claimed that only humans have minds, or consciousness, but this is surely wrong. Other primates are clearly able to think. So indeed are other mammals, cetaceans, and birds. But it is probably true that we humans have evolved ways of thinking that are unique, although derived from mental structures that were already present in our forebears. Moreover, our minds are not the phantoms of Cartesian dualism. Modern neuroscience is relentless in showing us that what we think of as mind and consciousness are due to the workings of the physical brain. Of course, we do not yet understand how consciousness itself comes about, although there is much speculation, so the identity of mind and brain must still be considered a working hypothesis. From a scientific viewpoint, the only real contender for the seat of the mind, or even the soul, is the brain.

So how do our minds—or brains—differ from those of other species?

Is Recursion the Answer?

In this book, I have argued that recursion might provide the key. Recursion might be said to capture several other properties previous claimed as unique to humans—language, episodic memory, mental time travel, and theory of mind. It also permits a degree of continuity, since each of those properties has precursors identifiable in nonhuman species. Language no doubt grew out of animal communication (pace Chomsky), perhaps more directly from gestural than from vocal communication, as I argued in chapter 4. Episodic memory and mental time travel might be considered refinements of memory capacities already evident in other species. And apes do show at least some glimmerings of a theory of mind.

Some have argued that it was not language per se that gave rise to the distinctive character of the human mind, but rather the ability to think in symbols. This was the theme of Terrence Deacon’s (1997) book The Symbolic Species, and more recently of an article by Derek C. Penn, Keith J. Holyoak, and Daniel J Povinelli, mentioned in chapter 8. The use of abstract symbols does of course characterize human language, especially speech. I argued in chapter 4, though, that the use of abstract symbols in language was more a matter of expedience than a distinctive component of the human mind. Chimpanzees and bonobos can be taught to use abstract symbols. Use of symbols has of course been exploited in mathematics and engineering, leading to the development of science and complex manufacture. But these are the accomplishments of Western civilization, and are generally foreign to indigenous peoples. In origin, at least, language is perhaps more a question of embodiment than of symbolic manipulation,18 and if it evolved from manual gestures, and indeed can persist in that form, we should look to processes not involving abstract symbols as the key to the human mind. That is why I suggest recursion as a possibility.

But is recursion truly a magic bullet, turning preexisting processes from cramped stereotypy to the soaring creativity we see in stories, poetry, art, music, and dance, not to mention the more oppressive dominance of machines and skyscrapers? The evidence reviewed in chapters 8 and 9 that great apes may have a limited ability to read the minds of others, whether expressed in acts of deception or in communicative pointing, or even in scrub jays’ apparent ability to prepare for a future event. We will need further careful analyses to determine whether such cases truly reflect a recursive ability, or whether they can be explained more simply in terms of association. One possibility, suggested in the previous two chapters, is that recursive processing can be discerned in some animal behaviors, but does not extend beyond a single level of embedding. Humans have the ability to share, to tell stories within stories, to develop devious social strategies, to play chess or poker, even to do mathematics and write computer programs that call recursively on other programs—all of these suggest runaway recursion that goes beyond first-order intentionality to perhaps as high as fifth or sixth order.

All of this need not imply a profound discontinuity, or threaten Darwinian principles. An appropriate biological analogy might be flight. Kangaroos can hop, dolphins can leap out of the water, even humans can create a meter or two of distance between themselves and the earth—although we now do rather better since we have constructed flying machines, inelegant though they are. But the evolution of wings created a profound discontinuity from incremental changes to limbs initially adapted to terrestrial movement. One small hop for animals became a giant leap for birds.19

From Descartes to Chomsky, the case for a discontinuity between us flightless humans and other species has been based primarily on the supposed uniqueness of language. Although Chomsky himself has made no claims about the human soul, he is in other respects a self-confessed Cartesian,20 and has long argued that language is uniquely human, primarily because of its recursive properties. We saw in chapter 2, though, that some languages, such as that of the Pirahã, may not make use of recursion. The prior significance of recursion may therefore lie, not in language itself, but rather in the nature of human thought that guides language and supplies much of its content. I argued in chapter 5 that the act of mentally reliving past events is a recursive process, analogous to calling a subroutine into a main routine. We can do this beyond the level of first-order recursion when we imagine imagining yesterday what we had planned to do today. In chapter 6 I extended this notion to the imagining of future events, or the construction of stories, and in chapter 7 I argued that these properties underlie at least some of the characteristics of language. The recursive tangle of human relationships also supplies the material for gossip, one of our favorite pastimes. The recursive structure of at least some languages, then, owes something to the recursive manner in which we construct episodic scenarios.

In chapter 8 I discussed yet another recursive function critical to the human condition. The capacity to know what others are thinking is recursive in that the mental processes of others are called into our own thoughts, and guide our social interactions. Rudimentary theory of mind can perhaps be inferred from the behavior of other species, but in humans goes beyond first-order recursion. The knowledge that we not only know what others are thinking, but also know that they know what we are thinking, may underlie what is perhaps the most fundamental human trait, the capacity to share. In chapter 9 I pointed out that language is just one manifestation of this. Language provides for the sharing of knowledge.

In the next two chapters, I try to set these recursive functions into human evolution itself.