The Gap, страница 1
THE SCIENCE OF WHAT
SEPARATES US FROM
A Member of the Perseus Books Group
Copyright © 2013 by Thomas Suddendorf
Published by Basic Books,
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Designed by Pauline Brown
Library of Congress Cataloging-in-Publication Data
The gap : the science of what separates us from other animals / Thomas Suddendorf.
Includes bibliographical references and index.
ISBN 978-0-465-06984-2 (e-book)1.Psychology, Comparative. 2.Psychology.I.Title.
10 9 8 7 6 5 4 3 2 1
For Nina, Timo, and Chris
ONE: The Last Humans
TWO: Remaining Relatives
THREE: Minds Comparing Minds
FOUR: Talking Apes
FIVE: Time Travelers
SIX: Mind Readers
SEVEN: Smarter Apes
EIGHT: A New Heritage
NINE: Right and Wrong
TEN: Mind the Gap
ELEVEN: The Real Middle Earth
TWELVE: Quo Vadis?
The Last Humans
THIS BOOK IS ABOUT YOU, what you are, and how you got here.
Biology puts beyond doubt that you are an organism. Like all living organisms, humans metabolize and reproduce. Your genome uses the same dictionary as a tulip and overlaps considerably with the genetic makeup of yeast, bananas, and mice. You are an animal. Like all animals, you have to eat other organisms—whether plant, fungus, or animal—for sustenance. You tend to approach things you want to eat while avoiding things that want to eat you, just as spiders do. You are a vertebrate. Like all vertebrates, your body has a spinal cord that leads up to the brain. Your skeleton is based on the same blueprint—four limbs and five digits—as that of a crocodile. You are a mammal. Like all placental mammals, you grew inside your mother and after birth received her milk (or someone else’s). Your body features the same terminal hair as a poodle. You are a primate. Like other primates, you have an immensely useful opposable thumb. Your view of the world is based on the same color vision as that of a baboon. You are a hominid. Like all hominids, you have shoulders that allow your arms to fully rotate. Your closest living animal relative is a chimpanzee. Yet it would be prudent of me to call you an ape only from a safe distance.
Humans tend to think of themselves as better than, or at least separate from, all other species on this planet. But every species is unique, and in that sense humans are no different. In the tree of life each species is a distinct branch with characteristics that set it apart from others. Humans differ from chimpanzees and other primates in some notable respects. We can lock our knees straight, have longer legs than arms, and habitually walk upright, freeing our hands to do things other than carry our weight. We have a chin. Our body surface is covered in sweat glands that provide a more effective cooling system than those of other primates. We have lost our canines and much of our protective fur, leaving males with the apparently pointless, but persistent, growth of beards. The iris of our eyes is relatively small and surrounded by white rather than dark sclera, making it easy for us to identify the direction of another’s gaze. Human females show no outward markers of their fertile phase, and human males lack a penis bone.
These are not exactly groundbreaking traits, compared to, say, the emergence of wings in birds, which predictably catapulted their bearers into a new sphere of possibility. Yet despite the paltry list of distinct physical attributes, we have managed to seize control of much of the planet. That is because our extraordinary powers do not derive from our muscles and bones but from our minds.
It is our mental capacities that have allowed us to tame fire and invent the wheel. They enable us to construct tools that make us stronger, fiercer, faster, and more precise, resilient, and versatile than any beast. We build machines that speed us from one place to the other, even to outer space. We investigate nature and rapidly accumulate and share knowledge. We create complex artificial worlds in which we wield unheralded power—power to shape the future and power to destroy and annihilate. We reflect on and argue about our present situation, our history, and our destiny. We envision wonderful, harmonious worlds as easily as we do dreadful tyrannies. Our powers are used for good as they are for bad, and we incessantly debate which is which. Our minds have spawned civilizations and technologies that have changed the face of the Earth, while our closest living animal relatives sit unobtrusively in their remaining forests. There appears to be a tremendous gap between human and animal minds, the nature and origin of which is the topic of this book.
WE HAVE BECOME SO SUCCESSFUL that many of us think a god singled our species out to run the world. Jewish, Christian, and Islamic traditions, for example, all share the fundamental belief that a universal god created humanity in his image, that only we are imbued with a soul, and that a glorious afterlife awaits those who follow a set of divine prescriptions. Nonhuman animals in these plots are cast as extras, and humans are given express rights to exploit them.
However, a couple of hundred years ago a range of inconvenient facts emerged to paint a very different picture of our place in nature. None were probably more profound than the extraterrestrial observations of Wilhelm Herschel. After moving from Germany to England, Herschel started to construct telescopes and study the night sky. His first breakthrough was the discovery of a new planet in our solar system, Uranus, in 1781. With the help of his sister Caroline and the royal support of King George III (before the madness), Herschel changed our view of the centrality of our Earth well beyond what Copernicus had done, cataloguing thousands of new star clusters and nebulae, and discovering the dynamic nature of the universe. He recognized that our solar system is traveling through space and that astronomical objects are born, change, and eventually die—a fate also in store for our own sun. He realized that starlight travels such enormous distances that some stars we see today have in fact already long died. The world turned out to be bigger, older, and more dynamic than anyone had anticipated.
Astronomy has demonstrated that we sit on a tiny speck in one of the billions of solar systems of the Milky Way, itself a galaxy among billions of others. This puts humanity, and all our troubles, in a radically new perspective—as Monty Python’s “Galaxy Song” urges us to recognize, while memorably summarizing some of the key discoveries about our place in the cosmos:
Just remember that you’re standing on a planet that’s evolving and revolving at 900 miles an hour
That’s orbiting at 19 miles a second, so it’s reckoned, a sun that is the source of all our power
The sun and you and me, and all the stars that we can see ar
In an outer spiral arm, at 40,000 miles an hour, of the galaxy we call the Milky Way.1
Herschel’s work gave humans a first glimpse at the really big picture. The realization that our planet and even our solar system are far removed from the center of anything cast serious doubt on previous theories that had put our species at the heart of a divine design. Indeed, with these discoveries, more secular views began to emerge. Pierre Laplace, for instance, proposed in 1799 that the sun, just as in other solar systems, originally condensed out of a nebulous cloud and then spun off the planets. When Napoleon asked him why there was no reference to God in his work, Laplace is said to have replied, “I had no need of that hypothesis.”
Scientific approaches also began to threaten long-held beliefs about our special position on Earth. Again, the Herschel family played a pivotal role. Wilhelm’s son John Herschel, who, like his father, served as president of the Royal Astronomical Society, wrote an influential book in which he promoted the new scientific approach, which allowed scholars to more effectively establish and accumulate knowledge. His inductive method of science had three parts: first, the gathering of data through observation and experimentation; second, the generation of hypotheses from these data; third, the testing of these hypotheses to see if they could be disproved. This systematic approach led to rapid progress across the disciplines, from astronomy to botany and from chemistry to geology.
Herschel’s book, together with that of Alexander von Humboldt, another romantic founder of modern science, was a key influence on Charles Darwin, who was inspired to make his own contribution to our understanding of our place in the world. Our relationship to animals would never be quite the same.
Descended from the apes? My dear, we will hope it is not true. But if it is, let us pray that it may not become generally known.
—REPUTED REMARK BY THE WIFE OF A CANON OF WORCESTER CATHEDRAL
DARWIN APPLIED HERSCHEL’S INDUCTIVE APPROACH in exemplary fashion. When he sailed around the world, he gathered enormous amounts of data on plants and animals. These led him to a new hypothesis explaining how species originated. On the Origin of Species was eventually published in 1859, after years of subsequent observation and experimentation had failed to disprove his theory of evolution by natural selection.
The theory is simple, elegant, and immensely powerful.2 Most importantly, 150 years of subsequent attempts have still failed to disprove it. In fact, science has unearthed a wealth of additional supporting evidence as well as further aspects of evolution, such as a detailed fossil record and the genetic foundation of life, which were unknown to Darwin. The implications of his work for humans’ view of themselves did not escape him. However, he only dared to make a brief reference to the human species in his seminal work. The notion that we have evolved like all other animals, that we share common ancestors with animals, that the same rules apply to us and them, that we are them, was unthinkable for many at the time—heresy even.
Nonetheless, twelve years later Darwin tackled the difficult but inevitable task of applying evolutionary theory to our own species head-on. In The Descent of Man he argued that humans, like all other animals, are the product of evolution; he went so far as to propose that humans’ closest living relatives are African apes. Today, various lines of evidence substantiate that this is indeed the case. Modern genetic comparisons have helped identify our animal family tree. Of all creatures compared to human DNA the two species of chimpanzee (common chimpanzees and bonobos) are clearly the closest match.3
In fact, the DNA of chimpanzees matches ours more closely than it does that of the African apes that look more like them: gorillas. In other words, from the perspective of chimpanzees, humans are their closest living relatives. Thus, by studying them we may perhaps learn more about the human condition than about the “animal condition.”
Though it has become widely known that we are descended from apes, it is still often misunderstood to mean we have evolved from chimpanzees. We did not. Chimpanzees could equally be argued to have evolved from humans. Common descent means humans and chimpanzees share a common ancestor, just as you and your cousin do on a much shorter time scale. Both chimpanzee and human lineages have had equal time to evolve since their lines of descent split. Recent genetic analyses and fossil finds suggest that the split occurred some six million years ago.
IN THE ABSENCE OF MICROBIOLOGICAL and fossil evidence, Darwin’s initial case for human evolution rested on signs of continuity. Descent with modification implies gradual change and therefore links between species. One can often find species with traits that are somewhat in between those of two other groups of species. Darwin, for instance, was most impressed with the Australian platypus, a so-called monotreme creature that appears to combine characteristics of mammals and reptiles (e.g., it has hair and lays eggs).4 The importance of signs of continuity to Darwin’s theory drove the search for so-called missing links, such as fish with rudimentary legs. To this day, almost every major fossil find is greeted in the press as a, or even the, Missing Link. (I will discuss the found links of human evolution in Chapter 11.) But even without fossils a strong case can be made for continuity between humans and animals.
The similarities in anatomy and bodily functions between humans and other primates are quite plain. We are made of the same flesh and blood; we go through the same basic life stages. Many reminders of our shared inheritance with other animals have become the subject of cultural taboos: sex, menstruation, pregnancy, birth, feeding, defecation, urination, bleeding, illness, and dying. Messy stuff. But even if we try to throw a veil over it, the evidence for continuity between human and animal bodies is overwhelming. After all, we can use mammalian organs and tissues, such as a pig’s heart valve, to replace our own malfunctioning body parts. A vast industry conducts research on animals to test drugs and procedures intended for humans because human and animal bodies are so profoundly alike. The physical continuity of humans and animals is incontestable. But the mind is another matter.
How can anyone prove a gradual descent (or ascent if you prefer) from animal to human mind? This was arguably Darwin’s greatest challenge. The seemingly vast gap between animal and human mind reeked of discontinuity. Even the co-discoverer of the principle of natural selection, Alfred Russel Wallace, and close scientific allies such as Charles Lyell were not convinced that natural selection could account for it.
Followers of René Descartes, who in the seventeenth century argued that animals are mere automata (machines governed by definable rules), thought that animals had no mental experience at all. Our own bodies may also be conceived of as mere machines; they are only the containers and vehicles of our exalted minds. In many cultures it is thought the mind governs and restrains the body. With the generous help of sanctions and taboos, the mind reins in the beast within. Now stop farting.5 This dualism between mind and body still penetrates much of Western science and society.
Yet modern science has established that the mind is inextricably intertwined with the body. Lesions to your brain, say, from a tumor or a stroke, have predictable effects on your mind. For example, a lesion in the temporal lobes just behind your ear can destroy your ability to comprehend language. A subdiscipline of modern psychological science called “embodied cognition” examines more subtle links, showing that people’s mental experiences and judgments change when their bodies are slightly manipulated. For instance, one finds the same situation more or less funny depending on whether one has a pen in the mouth or not. Try it while watching your favorite comedy. The pen prevents overt smiling and laughing, and thus reduces the subjective experience. People seem to judge a hill to be steeper when they are wearing a heavy backpack than when they are not. There are many ways to demonstrate that states of the body influence the mind. Ultimately, when our brain dies, all evidence points to the conclusion that our mind does, too.
What, then, about the brains of our primate cousins? Around the time On the Origin of Species ap
The extreme position that animals have no minds at all became hardly tenable, given the continuity evident in brains, coupled with the evidence linking mind and brain. Animals’ neurochemical and behavioral reactions to physical insult, for example, closely resemble ours. They apparently mind being injured. And like us, they do not seem to mind injury when under anesthetic.
It is reasonable to assume, then, that many animals have the basic foundation of conscious experience. Yet people often reserve the word “consciousness” for higher functions of thinking. After all, Descartes was convinced of his own existence only on the basis of reflection: “I think therefore I am.” But consider the Czech novelist Milan Kundera’s astute reply: “‘I think therefore I am’ is the statement of an intellectual who underrates toothache.” When you have a toothache, no further thinking is required to be sure of your existence and the fact you mentally experience things. The next time you doubt your own existence, go to the dentist (and decline anesthetic). The psychologist William James argued at the end of the nineteenth century that consciousness gives animals “interests.” Because animals can feel, survival is made an imperative rather than a chance rule. They actively seek the experience of pleasure and relief from pain. Rats with inflamed joints, for example, will choose painkillers over usually preferred tastes when given the opportunity.
Even if we grant animals some mental experience, human minds appear to be vastly different from animal minds. In The Descent of Man Darwin tackled the problem of the apparent mental gap by comparing psychological characteristics such as emotion, attention, memory, and abstraction in animals and humans. Citing various anecdotal accounts he argued that animals have more sophisticated minds than is often assumed, and concluded that human minds differ only in degree and not in kind. The mental difference between ape and fish was greater, he argued, than that between ape and human. These conclusions remained controversial, even though Darwin predicted in On the Origin of Species that the study of the mind would be revolutionized by evidence for continuity: “In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.”