He must have peeked into quite a distant future, as over 150 years later psychology has not yet been placed on this foundation. Theories and scientific traditions from behaviorism to cognitive psychology, from Freudian psychoanalysis to ethology, have attempted to unravel various intertwined secrets of behavior, evolution, and the mind, yet there is still no consensus on what mental powers humans share with which other animals, nor have such questions been central to psychological inquiry. Even evolutionary psychology, which studies the nature of the human mind as a product of a long evolutionary history—“Our modern skulls house a stone-age mind,” as two of its founders, Leda Cosmides and her husband, John Tooby, claim—has not yet taken seriously the challenge of investigating the apparent gap. Whole textbooks on evolutionary psychology barely mention our closest animal relatives, the great apes, or even our ancestral species.
Nevertheless, throughout the last century the work of some researchers, starting with pioneers such as Wolfgang Köhler examining the minds of chimpanzees, has been directly relevant to understanding the gap. In recent years, studies in comparative animal psychology have increased dramatically, and a clearer picture of the competences and limits of various nonhuman minds is finally emerging. Together with a more sophisticated understanding of the human mind and its development, I think we are finally in a much better position to tackle the question of what separates us from other animals.
Although signs of continuity between the minds of humans and animals were critical to Darwin’s original case for human evolution, today we know that whatever the size and nature of the gap turns out to be, the evolutionary account is compellingly supported by genetic and fossil evidence. Even vast gaps need not be incompatible with evolution through descent with modification. Evolutionary biology can accommodate the possibility of profound changes, as illustrated, for instance, by Stephen Jay Gould and Niles Eldredge’s arguments for rapid transitions followed by periods of relative stability. Most important, questions of continuity or discontinuity are, of course, about the evolutionary past and not about the present state of affairs. Current gaps are a function of what forms happen to have survived to this day. There is no need to assume that intermediate links must have survived (or that fossils of such links must be found). Indeed, most species that ever existed on Earth are extinct.
GREAT APES HAVE NOT ALWAYS been our closest living relatives. Only two thousand generations ago humans still shared this planet with several upright-walking, fire-controlling, tool-manufacturing cousins, including big Neanderthals (Homo neanderthalensis) and small “Hobbits” (Homo floresiensis). With its various bipeds it was a world reminiscent of Tolkien’s Middle Earth. Our ancestors forty thousand years ago would have had much less reason to believe they were far removed from the rest of the Earth’s creatures. We were but one of a group of similar species.
Perhaps because of the search for continuity and links, a picture persists of our ancestors evolving in a straightforward, single, and direct trajectory, up a stairway to Homo sapiens. This was not the case. For millions of years, many species of humans, technically called “hominins,” wandered the planet and sometimes shared the same valleys. For example, between 1.6 and 1.8 million years ago, there were probably six or seven species in the human family,6 ranging from the slender Homo habilis, makers of stone tools, to the stockier Paranthropus robustus with their massive, powerful jaws. There were also other types of apes such as the spectacular Gigantopithecus—an ape three meters tall that may have resembled Chewbacca from Star Wars. Our direct line of descent is only one branch on a flourishing, bushy tree of closely related species.
Some of these species were immensely successful. Paranthropus boisei, a heavily built hominin with a wide face, and the tall and large-brained Homo erectus each graced the planet for well over a million years. Modern humans have been here a mere fifth of that time. While there are clear signs of gradual change in, for instance, increasing cranial capacity and tool sophistication, diversity is also in evidence. Several new species have been described in the last decade. If the frequency of recent discoveries is anything to go by, archeologists will find many more fossils of hitherto unknown relations. We can expect an ever more complex family tree.
Yet today Homo sapiens is the only member of the human family left on this planet, and it so happens that a few species of great apes are our closest remaining relatives. A gap is defined by both of its sides. In an important sense, then, the answer to the question of why we appear so different from other animals is that all closely related species have become extinct. We are the last humans.
WHY IS OURS THE ONLY surviving lineage in this multitude of human forms? Why did the others die out? Radical environmental changes, such as ice ages and volcanic eruptions, are often responsible for extinctions. Such challenges have no doubt played a significant role in our relatives’ past as well. The various extinctions were probably complex processes involving a multitude of factors, and the constellation of these factors likely differed in the demise of different hominin species. But for the disappearance of our close relatives we should consider another potential culprit: our ancestors.
Humans have been responsible for the demise of many species in recent times and, although we have no direct evidence, may well have had a hand in the extinctions of Neanderthals and other close relatives. Once our ancestors had managed to control much of the classic ecological challenges of survival, including predation by big cats and bears, members of the human family probably became their own primary adverse force of nature. We are more likely to be threatened, coerced, or killed by another human than by any animal. Aggression and conflict may have greatly affected hominin evolution.
A technologically advanced population can have devastating effects on other groups. People may be exterminated not only through killing but also indirectly through competition, habitat destruction, or even the introduction of novel germs. In his book Guns, Germs, and Steel the evolutionary biologist and geographer Jared Diamond vividly recounts the extraordinary case of a mere 168 conquistadors ransacking the Inca Empire in 1532. Most Incas were, in fact, killed by smallpox. The invaders brought the deadly disease, which swept ahead of their advance. The wholesale loss of life was an advantageous side effect for the Spanish—a result of hundreds of years of suffering from the disease in Europe. But some conquerors may have been aware of such causal chains and actively facilitated the process, guaranteeing widespread deaths as a result. British colonists, for example, have been accused of intentionally giving blankets infested with smallpox to native North Americans. It is unclear how common such callous acts were. What is evident is that humans are capable of them.
Yet we are also capable of extraordinary cooperation, empathy, and kindness. We can, and I would hasten to say should, make ethical choices that avoid exterminations of other people or species. As Steven Pinker recently documented in The Better Angels of Our Nature, violence has gradually declined over the course of history. In other words, war, blood feuds, murder, rape, slavery, and torture have been more commonplace in our past. Evidence of violent conflict goes back to prehistoric hunter-gatherers, but it is unknown when this dark side first emerged. Common chimpanzees are the only other primate species known to cooperate to directly kill members of their own species. So cooperative aggression may have ancient roots indeed.
No doubt our forebears at times would have also attempted to interbreed with close relatives, and they may have assimilated those with whom they could successfully reproduce. There is some anatomical evidence that humans and Neanderthals interbred, and in 2010 the first genetic evidence demonstrated that Europeans and Asians, in contrast to Africans, still carry some Neanderthal inheritance estimated at between 1 percent and 4 percent.7 I am part Neanderthal. In December 2010, a thirty-thousand-year-old finger and tooth of another previously unknown human family member were described. Genetic analysis revealed that these so-called Denisovans were distinct from modern humans and from Neanderthals. They contributed a
bout 5 percent to the genome of modern-day Melanesians.
Although sometimes represented as alternatives, making love and making war are not mutually exclusive possibilities. There is love as well as rape in times of war, and romance can result in conflicts. One way or another, it seems likely our forebears played important roles in the disappearance of at least some of our closest relatives. The reason the current gap between animal and human minds seems so large and so baffling, then, may be because we have destroyed the missing links. By displacing and absorbing our hominin cousins, we might have burned the bridges across the gap, only to find ourselves on the other side of the divide, wondering how we got here. In this sense, our exceedingly mysterious and unique status on Earth may be largely our own, rather than God’s, creation.
What follows is the story of the chasm that currently separates human and animal minds. Chapters 2 and 3 first take a closer look at what is known about our closest remaining relatives and how we can establish animal mental capacities. In Chapters 4–9 I examine the major claims about what makes our minds unique: language, foresight, mind reading, intelligence, culture, and morality. I explain what we know about the nature and development of the human faculties and assess what is known about parallels in animals. Although some species have communication systems, can predict what happens next, can solve certain social and physical problems, have traditions and perhaps even empathy, we will discover that human minds are distinct for a small number of recurring reasons. Chapter 10 distills what is common about the gap in all of these domains and why. Our prehistoric forebears and clues about the evolution of our minds are the focus of Chapter 11. Finally, in Chapter 12 I consider the future of the science of what separates us from other animals, as well as the future of the gap itself.
1Our galaxy itself contains a 100 billion stars, it’s a 100,000 light-years side-to-side It bulges in the middle, 16,000 light-years thick, but out by us it’s just 3,000 light-years wide We’re 30,000 light-years from galactic central point, we go round every 200 million years And our galaxy is only one of millions of billions in this amazing and expanding universe.
The universe itself keeps on expanding and expanding, in all of the directions it can whiz As fast as it can go, at the speed of light you know, 12 million miles a minute, and that’s the fastest speed there is
So remember, when you’re feeling very small and insecure, how amazingly unlikely is your birth And pray that there’s intelligent life somewhere up in space, because there’s bugger all down here on Earth.
“Galaxy Song,” Eric Idle/Terence Jones (PKA John Du Prez) ©1983 Kay-Gee-Bee Music. Used by permission of EMI Virgin Music Publishing Australia Pty Limited (ABN 71 002 884 915) PO Box 35, Pyrmont, NSW 2009, Australia International copyright secured. All rights reserved.
2From his travels Darwin noted that characteristics of animals and plants seem to fit their function, and that populations vary in relation to their geographic isolation from each other. He also noted that no two organisms are exactly identical—be that two dogs or two spiders. Given finite resources and competition, some variants inevitably leave more successful descendants in the next generation than others. In other words, some inherited variations have an adaptive advantage over others. If these are continually passed down the generations, the number with this advantage increases and eventually replaces lineages without them. Over large time spans organisms come to function better in their environment, and eventually, especially in geographic isolation, descent with modification results in different species. This is Darwin’s theory in a nutshell.
3Note that figures such as a 99.4 percent match between chimpanzee and human DNA, though frequently cited, can be misleading. Common sense, for example, suggests that a zero percent match would indicate that two species are unrelated. However, given that genetic code of all creatures on Earth consists of only four molecules (adenine, thymine, guanine, and cytosine), the baseline is 25 percent and not zero percent. That is, if you compare a string of only one molecule, say, adenine, with the DNA of any species, be that rhubarb, porcupine, or human, you will find that on 25 percent of all DNA locations there is a match. About 25 percent of DNA is adenine. Furthermore, in addition to single base-pair substitutions, structural differences such as insertions, deletions, and duplications need to be considered when comparing genomes. For these, and some other reasons, one should take such figures like the 99.4 percent match with a grain of salt. Nonetheless, the relative match between different species can be interpreted in a straightforward manner.
4This is especially interesting given that there are no truly native placental mammals in isolated Australia. Today the platypus is thought to be a surviving member of an early branch of mammalia, and a later branch is thought to have evolved into modern placental mammals and marsupials.
5Do you find such an example offensive or misplaced for a serious discussion of human nature? Well, that is part of the point. We often like to think of ourselves as better than that.
6Traditionally these are Homo habilis, Homo erectus, Homo ergaster, Homo rudolfensis, Paranthropus robustus, and Paranthropus boisei. In 2010, a seventh species, Australopithecus sediba, was described.
7The logic is simple. When Neanderthal DNA is compared to different African groups of humans, they are equally different from each group. If, however, the DNA is compared to a European and an African, it more often matches the European than the African DNA. The same is true for tests with Chinese DNA. This suggests that when modern humans migrated out of Africa, they mixed with Neanderthals, presumably in the Middle East, where fossil evidence demonstrates prolonged cohabitation (see Figure 11.10), and then carried the Neanderthal component of their genome to the world outside of Africa.
TWO
Remaining Relatives
WE ARE PRIMATES. PRIMATES ARE generally adapted to life in trees and, because of the fatal risk of falling out of them, have evolved novel and sophisticated capacities for accurate seeing and grasping. Primates typically have forward-facing eyes and stereoscopic color vision, on which they rely more than on their noses. They have lost the whiskers characteristic of other mammals and also have a relatively reduced olfactory (smell-processing) brain.1 Primates have evolved grasping hands with five separate digits, and many feature a versatile opposable thumb and fingernails rather than claws. We would not perceive and interact with the world the way we do were it not for our primate heritage.
Compared to those of most other animals, primate brains are large and primate minds are smart. When observing the lives of, say, gorillas, one may well wonder why they would need smarts. Gorillas often do little more, it seems, than sit in the giant salad bowls of the forest, munching away. This observation prompted the philosopher Nick Humphrey to propose that it is social problems, rather than physical challenges, that might have driven the evolution of primate intelligence. This idea has increasingly attracted followers because most primates are indeed deeply social, and our closest relatives are especially so.
It is hardly an exaggeration to say that a chimpanzee kept in solitude is not a real chimpanzee at all.
—WOLFGANG KÖHLER
The intricacies of primate social lives have been extensively documented by field observations, which reveal that group structures are held together through relationships maintained by individual attention to others within the group. Primates are fond of grooming; it is relaxing and leads to release of endorphins and oxytocin, and sometimes to the groomed individual falling asleep. As tension and parasites are removed, social bonds are formed. Alliances are forged and repaired. The larger the group, the more time its members tend to spend grooming each other. While other animals aggregate in much larger numbers than primates do—wildebeest or sardines, for example, live in groups numbering many thousands—the individuals may be entirely anonymous to one another. Primates, on the other hand, know each individual group member.
In addition, primates appear to have some understanding of the relationships other group members
have in terms of dominance, kinship, and friendship. Upon hearing the call of her infant, a vervet monkey mother will look toward the origin of the call, whereas other group members look to the mother—in apparent recognition that her infant is calling. Close observation of primate groups reveals that such knowledge is essential to their social lives. Therefore a fight between two individuals may affect the relationship between other members of the group. I once observed a young chimpanzee sneak up to an older female, holding a branch behind his back. When the female tried to groom the juvenile, he suddenly hit her with the branch and ran away, chased by the enraged female. This event had ripple effects throughout the community, as different chimpanzees appeared to take sides. Retaliations target not only perpetrators but sometimes also their kin or associates.
Primate social lives can be multilayered affairs. Achieving high rank is a function not always merely of brute strength but also of shrewdness. By grooming the right individuals one can gain support in power struggles. Social problems therefore require significant attention and consideration on the part of individual primates, especially as group size increases. In fact, evolutionary psychologist Robin Dunbar established that the greater the typical group size of a primate species, the bigger their brain—or, more precisely, the ratio between the neocortex and the rest of the brain. The larger the group the more cognitive power an astute social player may require to keep track of the increasingly complex web of information.
The Gap Page 2