The Accidental Species: Misunderstandings of Human Evolution

by Henry Gee

  What we see of the world around us is far from a detailed panorama in which everything is in focus, up and down, and from side to side, as if our eyes were cameras. We pay attention only to a small area at any time. If this seems counterintuitive, go take a look at any landscape by the photographer Ansel Adams, and ask yourself why, for all its realism, it looks weird and dreamlike. The reason is that everything is in focus, from the rocks in the foreground to the mountaintops in the distance. We don’t actually see the world like that.

  Color is likewise tricky. Is there a fundamental quality of, say, “red” that’s “out there” in the world? Why do we interpret electromagnetic radiation in a particular range of frequencies as “red”? When you imagine a red sports car, how “red” is it in your mental picture of a sports car? If I hadn’t asked you to imagine it, would you have seen it as “red” or—perhaps—as a label you might find in a paint-by-numbers kit, that stands for “red” but isn’t actually “red” itself? If this “label” isn’t “red,” what color is it? Does it have any color at all? If it does, would you have ascribed a color to it had I not inquired about it?

  Dennett argues that there isn’t any objective reality to “red,” in the same way that there isn’t a central command unit of the mind. What is there, instead, is a reaction that’s been honed by natural selection in which the visual system pays especial attention to the electromagnetic radiation in the particular frequency range that is characteristic of ripe fruit when seen against a background of green leaves,10 or, as it may be—and not uncoincidentally—the swollen genitalia of potentially receptive mates. Whether we call it “red,” “borogove,” or “manxome” is immaterial, because the explanation does not require the postulation of any kind of self-conscious inner life.

  Sentience, then, is a slippery customer. One might be tempted—I am so tempted—to say that it doesn’t exist—not, at least, as a discrete quality.

  But if that is the case, how can we interpret the behavior of Clayton’s scrub jays, or indeed of any human or animal that shows a “theory of mind” or various degrees of what Robin Dunbar calls “intentionality”?

  I think that whereas such behavior appears to show that creatures have a sense of what is going on in the minds of others, that appearance is illusory, conditioned by our own preconceptions about sentience—that it is discrete, and, moreover, that it happens in a Cartesian theater. To put it another way, we interpret the scrub jays’ behavior for what it is because we recognize that behavior in ourselves, and we attribute that behavior to a “theory of mind.” We therefore project that theory into the heads of jays, rather in the way that our minds make sense, retrospectively, of things that go bump in the night.

  What the scrub jays are actually doing is exhibiting a behavior that is selectively advantageous in a social situation. Once that is realized, the necessity for a quality called “sentience” becomes moot, for natural selection does all sorts of wonderful things, produces all sorts of exquisite adaptations that, when studied casually, have all the appearance of intention and design, yet we know that nothing of the kind has taken place. In this light we can perhaps see the idea of sentience as the last great conceit of that linear view of evolutionary progress that has humanity marching at its head, rather than of Darwin’s original concept of a tangled bank upon which circumstances changed from one instant to the next with no end in view, no purpose to attain. The tangled bank might, indeed, make a better metaphor for the workings of the mind than the Cartesian theater—so clean, so tidy, and so wrong.

  If there is no Cartesian theater, what becomes of the “self” that both watches and takes part? Does the “self” really exist? If there is no “self,” you might ask, whose arthritis is this? In my view the self is as illusory as sentience and the Cartesian theater. To reprise that old limerick:

  There was a faith-healer of Deal

  Who said, “I know that pain isn’t real:

  But when I sit on a pin

  And it punctures my skin,

  I dislike what I fancy I feel.”

  The idea of a “self” is not only illusory—it’s unnecessary. There need be no “inner life” if such traits can be judged in the context of externals, of observable behavior and social interaction. There is an area of research into animal behavior in which it is shown that animals of the same species may have measurably different “personalities.”11 The idea of “personality” in this context is deliberately quite narrow. A “personality” means a self-consistent set of responses that makes a discrete behavioral repertoire or “syndrome.” For example, some animals tend to be more outgoing than others—bolder and more risk taking than their fellows, who might be shyer and more risk averse. Anecdotally, anyone who owns a dog will be aware that pets have personalities. My golden retriever, Heidi, is phlegmatic and laid-back, whereas my Jack Russell terrier, Saffron, is excitable, a real live wire. Domestic dogs belonging to distinct breeds are, however, highly inbred, and their temperaments are to some degree breed-specific. Some dog breeds are prone to behavior that parallels various psychiatric problems in humans, such as anxiety or obsessive-compulsive disorder: the fact that dogs are inbred compared with humans is allowing researchers to get a fix on the genetic roots, if any, of such traits, in the hope that the human cognates of such genes might be identified.12

  None of this bears on whether dogs are sentient. Strictly, animal personalities reflect consistent behavioral differences of possible selective value13—researchers in this field scrupulously avoid the philosophical quagmires of sentience and theories of mind. In which case, it is perfectly possible to view the behavior of apparently sentient creatures such as crows and people in this same dispassionate manner—as it is the behavior of creatures that have little or nothing in the way of brains at all.

  Aha, I hear you cry—there is an observable way to discern whether an animal has a sense of “self,” and that’s by mirror self-recognition. That is, whether an animal can look at its reflection in a mirror and recognize it as a representation of itself rather than another animal, or nothing at all. Cats and dogs don’t have this sense. When they look in a mirror, they definitely see something, and by the aggressive attitude they sometimes adopt, it is likely to be another cat or dog. It doesn’t see its “self” in its reflection.

  The classic test for mirror self-recognition is the “mark test.” The experimenter marks an animal in such a way that it cannot see the mark except in its reflection. If, on seeing the reflected mark, the animal looks for it on its own body, it is therefore able to recognize its reflection as itself rather than another animal or anything else. Humans are able to do this from a very early age,14 and the mark test has been passed by the great apes, elephants, dolphins, and—you’ll not be surprised to learn—at least one member of the crow family.15

  By now you’ll have spotted the trapdoor lurking underneath such research. If you haven’t, it’s this—as with theories of mind, the results of such tests are biased by our own capabilities and expectations. Being, as we are, visual creatures, who recognize one another largely by visual inspection, we tend to judge other creatures by the same yardstick, and unconsciously rank them according to the age-old ladder of creation in which humans are at the top. We have no idea whether creatures are able to recognize themselves using other senses, such as smell. Given our ignorance of the olfactory universe of dogs, for example, we simply don’t know whether dogs can identify their own smells. However, observing one’s dogs as they sniff lampposts and one another’s bottoms, one suspects that at the very least dogs are able to recognize and distinguish between other dogs, and possibly between different humans.

  Is there any experimental evidence for self-nonself recognition that is not based on vision? Yes—plenty of it. For example, it is known that quite a few animals are able to distinguish between kin and nonkin,16 presumably through olfactory cues in urine. In mammals, at least, this recognition is based on a region of the genome called the major histocompatibility complex,
or MHC. Breakdown products of MHC proteins are excreted in the urine and can be detected by creatures of sufficiently sensitive sniffage. The MHC is part of the immune system—it produces a set of molecular markers of incredible variety that identify any matter in the bloodstream that comes from another organism, such as an infectious agent. It is this system that makes matching organ donors with recipients so difficult. The same system is exploited by animals, including social animals, to tell the difference between close relations and nonkin, perhaps as a way to avoid inbreeding. The MHC is really just a riff on a very basic self-nonself recognition system seen in many creatures, even some quite lowly ones.

  The ability to recognize oneself in a mirror is, therefore, a somewhat contrived special case of a much more general ability to distinguish between oneself and other creatures, based on senses that aren’t necessarily visual. If one thinks of mirror self-recognition as a good marker of sentience, try this thought experiment. Would we humans, with our notoriously poor sense of smell, be able to distinguish between ourselves and other humans on the basis of smell—from urine samples, body odor, or sniffing or licking one another’s’ bottoms or genitalia—with the same reliability as we can tell the difference between people by sight?

  If not, why should we expect other creatures, perhaps with visual capabilities that aren’t as good as ours, to recognize one another by sight alone?

  Sentience, that seemingly quintessential human characteristic, is an artifact maintained by human exceptionalism—and has given up with hardly a whimper.

  Afterword: The Tangled Bank

  Several people who read excerpts of the draft of this book have, understandably, been distressed that I should walk away from this extended dustup without leaving even one tiny crumb of comfort. What people want, I guess, is the conventional Hollywood happy ending. In the movies, the aliens never destroy the earth and disappear, leaving a charred ruin. No, the human underdogs fight back against overwhelming odds, employing well-known heroic virtues such as motherhood and apple pie, and drive the alien insectoid scum to destruction.1 It’s a tale as old as time, to coin a phrase: as old as David vs. Goliath, Frodo vs. Sauron, Luke vs. Vader, Harry vs. Voldemort.

  We human beings do like to tell stories, and the conventional picture of evolution as a stately and predictable procession with humanity at its head is just that—a story. As such, it speaks both to a profound misreading of Darwinian evolution, and to assumptions based on the fossil record that it cannot support, and never will.2

  Appeals to various human traits sometimes regarded as qualitatively “special” likewise fail. This is because the various traits expressed by organisms, human beings included, don’t represent way stations between Ape and Angel, or even one species and another, but contingent, makeshift compromises made in response to a number of different factors, some reinforcing one another, others acting in opposition. Because of this, such traits cannot be treated in isolation. Organisms don’t evolve first one trait and then another, hauling themselves up the ladder of creation at each step, but in an integrated way, as you’d expect for creatures living on the tangled bank of Darwin’s imagination.

  Bipedalism, for example, didn’t evolve, on its own, “in order that” we might free our hands to make tools, share food, or any other purpose conferred after the fact. To be sure, such factors might have been involved in the transition, along with sexual selection, the evolution of a social life, the invention of cookery, the growth of the brain, the dependency of infants, the further growth of social groups, the invention of technology, the evolution of the menopause, the evolution of language, the telling of tales, and so on. Bipedalism required a wholesale change in hominin anatomy, yet, considered as a whole, was just one change among many that happened in the hominin lineage, a change that facilitated (or impeded) changes elsewhere in the body, and was in turn influenced by these changes.

  Even after the foregoing, one might argue that humans aren’t qualitatively special for what they are, nor even for how they got that way, but for what they’ve achieved. One might well ask, for example, whether humans are unique in that they have a conception of the divine, the numinous. It’s impossible to know. The gospels of crows, the dreams of dolphins, and the speculations of anthills might be forever beyond our grasp.

  Books of this kind usually end by looking forward to humanity’s glorious future in space (if optimistic), humanity’s capacity for destructive warfare (if pessimistic), or humanity’s destruction of the environment (ditto). Humans aren’t unique in any of these achievements, either. Bacteria can survive exposure to space,3 even without space suits, and there seems no good reason why, if living organisms can withstand hard radiation, they cannot survive routinely in the uppermost atmosphere. Ants are accomplished warriors. And any effects we might have on the environment, while regrettable in themselves, are puny compared with the effects of the bacteria that, billions of years ago, invented a nifty scheme for harvesting sunlight to drive a process in which plentiful carbon dioxide and water were made into food. This process, oxygenic photosynthesis, changed the world utterly, not least because its by-product, molecular oxygen, was and is both toxic and corrosive. The emission of large amounts of oxygen into the atmosphere drove much of the then-existing biosphere to the brink of extinction and rotted the very bones of the earth. We are the by-products of the terrific selective forces for creatures that could withstand this assault, and even use it to their advantage.

  All such scenarios, though, are told as stories—we cannot help it. They demand narrative, characterization, and a moral payoff, even if the action happened billions of years ago and the protagonists were bacteria. Stories are something we humans can’t live without. They fuel our most disposable gossip and inform our deepest speculations. Perhaps, then, the capacity to tell and appreciate stories is the one thing that marks human beings from the crowd.

  And they all lived happily ever after.

  Or did they?

  Notes

  PREFACE

  1 J. L. Franzen et al., “Complete primate skeleton from the Middle Eocene of Messel in Germany: Morphology and paleobiology,” PLOS One 4 (2009): e5723, doi:10.1371/journal.pone.0005723.

  2 See my essay “Aspirational thinking,” Nature 420 (2002): 611.

  3 H. Gee, “How humans behaved before they behaved like humans,” London Review of Books, 21 October 1996, 36–37. For the record, the books I reviewed were C. Stringer and R. McKie, African Exodus: The Origins of Modern Humanity (London: Cape, 1996); R. Foley, Humans before Humanity (London: Blackwell, 1995); C. Tudge, The Day before Yesterday: Five Million Years of Human History (London: Cape, 1996); A. Walker and P. Shipman, The Wisdom of Bones: In Search of Human Origins (London: Weidenfeld, 1996); and J. Shreeve, The Neanderthal Enigma: Solving the Mystery of Modern Human Origins (London: Viking, 1996). But wait, there’s more—two years earlier in the same magazine I’d reviewed three others (H. Gee, “What’s our line?,” London Review of Books, 27 January 1994, 19), and they were E. Trinkaus and P. Shipman, The Neandertals: Changing the Image of Mankind (London: Cape, 1993); C. Stringer and C. Gamble, In Search of the Neanderthals: Solving the Puzzle of Human Origins (London: Thames and Hudson, 1993); and J. Kingdon, Self-Made Man and His Undoing (New York: Simon and Schuster, 1993).

  4 J. Maddox, What Remains to Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race (New York: Touchstone, 1998).

  5 P. Pearson, book review, Palaeontology Newsletter 44 (2000): 36–38.

  6 “When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things.” 1 Corinthians 13:11.

  CHAPTER 1

  1 H. Gee, “UK nuclear operators unhappy with radiation dose advice,” Nature 330 (1987): 596.

  2 F. Gibson et al., “A type VII myosin encoded by the mouse deafness gene shaker-1,” Nature 374 (1995): 62–64.

  3 R. A. Lutz and J. R. Voight, “Close encounter
in the deep,” Nature 371 (1994): 563.

  4 P. Brown et al., “A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia,” Nature 432 (2004): 1055–1061.

  5 See for example S. O’Connor, “New evidence from East Timor contributes to our understanding of earliest modern human colonization east of the Sunda Shelf,” Antiquity 81 (2007): 523–535; and B. David et al., “Sediment mixing at Nonda Rock: Investigations of stratigraphic integrity at an early archaeological site in northern Australia and implications for human colonization of the continent,” Journal of Quaternary Science 22 (2007): 449–479.

  6 A. Brumm et al., “Hominins on Flores, Indonesia, by one million years ago,” Nature 464 (2010): 748–752.

  7 The term “hominin” might be unfamiliar and deserves a note of explanation. It means any species, living or extinct, that is more closely related to modern humans (Homo sapiens) than to our closest living relatives, the chimpanzees (Pan troglodytes and Pan paniscus). Importantly, this designation does not demand or imply direct ancestry, although it does not rule it out. The most we can say of any hominin other than Homo sapiens is that we are related to it, at the very least as cousins. I discuss this concept of relatedness and much else besides in my book In Search of Deep Time.

  8 M. J. Morwood et al., “Archaeology and age of a new hominin from Flores in eastern Indonesia,” Nature 431 (2004): 1087–1091.

  9 M. R. Palombo, “Endemic elephants of the Mediterranean islands: Knowledge, problems and perspectives,” in G. Cavarretta, ed., The World of Elephants—International Congress (Rome: CNR, 2001), 486–491.

  10 E. M. Northcote, “Size, form and habit of the extinct Maltese swan Cygnus falconeri,” Ibis 124 (1982): 148–158.