In summary, approximately two million years ago some hominins living in eastern Africa began developing larger brains and becoming significantly smarter. Given the fact that hominin brains had grown very little in size during the preceding four million years, this development was unexpected and remains unexplained. The brain areas that increased disproportionately included specific parts of the frontal and parietal lobes; these areas have been linked to intelligence using modern neuroimaging techniques. This was the first of the five major cognitive advances that would ultimately produce modern Homo sapiens and the gods who followed. Although Homo habilis had become smarter than other hominins living at that time, they were not aware that they were smarter. That would come next.
2
HOMO ERECTUS
An Aware Self
The evolution of consciousness can scarcely be matched as a momentous event in the history of life.
—Stephen Jay Gould, Ontogony and Phylogeny, 1977
Homo habilis would merely be the starting gun for the beginning of the human race. Its modestly increased brain capacity made it smarter, so it could make tools, use the tools to make other tools, and store tools for future use. The frontal-parietal brain network associated with intelligence was developing and would continue to develop for the next two million years, making the offspring of Homo habilis progressively smarter. Hominins had started down the path that would ultimately lead them to, among other things, a belief in gods.
A second major cognitive leap forward for hominins was demonstrated by Homo erectus. These hominins first appeared approximately 1.8 million years ago and lived until 300,000 years ago, thus existing for 1.5 million years. Previously, it was thought that Homo erectus had descended from Homo habilis, but recent archeological research suggests that Homo habilis and Homo erectus lived side by side in what is now northern Kenya “for almost half a million years,” making this evolutionary sequence less likely. In 2012 a third hominin species was discovered in Africa that had lived in the same area at about the same time; presumably, there were additional early species, still to be discovered, that will help to clarify the relationships between the earliest hominin species.1
Homo erectus was taller than Homo habilis and had a much bigger brain. Adults averaged five feet in height and weighed about 125 pounds. According to Andrew Shryock, an anthropologist at the University of Michigan, and Daniel Smail, a historian at Harvard University, Homo erectus had physical features, especially its arms and toes, that “suggest that these hominins had more or less given up climbing trees, implying a completely terrestrial lifestyle.” The brains of Homo erectus ranged from 750 to 1,250 cubic centimeters, averaging about 1,000 cubic centimeters; therefore, their brain was about 60 percent larger than the brain of Homo habilis. Since the average brain capacity of modern Homo sapiens is about 1,350 cubic centimeters, the largest Homo erectus brains overlapped in size with the smallest Homo sapiens brains. Thus, it has been claimed with some justification that Homo erectus was “the first hominid [hominin] species whose anatomy and behavior justify the label human.”2
The larger brains of Homo erectus led, as might be expected, to new behavioral horizons. Their stone tools, some of which have been dated to more than 1.7 million years ago, went from being crudely flaked on one side, like those made by Homo habilis, to being elegantly flaked on two sides. This new tool, generally referred to as a biface or handaxe even though it was really just an elegantly sharpened rock, sometimes weighed several pounds and was significantly sharper than earlier tools. According to archeologist Kenneth Feder, making a good stone handaxe “takes great skill, precision and strength.… Very few of my students ever developed proficiency in handaxe production.”3
In addition to handaxes, Homo erectus also made what appear to be the first weapons specifically manufactured for hunting animals. These were wooden spears of up to six feet in length and sharpened at both ends. Eleven such spears found at a German site were apparently used to hunt wild horses. At sites in southern England and Spain, it appears that Homo erectus hunted other large mammals, including bison, deer, bears, and elephants. Such hunts would have required the cooperation of a large number of people. In addition to the sharpened wooden spears, stone-tipped spears dated to 460,000 years ago have recently been found in South Africa.4
Homo erectus was apparently also the first hominin to control and use fire. Exactly where and when this initially occurred is a matter of debate; there is good evidence for the controlled use of fire by 790,000 years ago, and by about 400,000 years ago the controlled use of fire had become widespread. Fire can be used for warmth, for light, for protection from predators, and for hunting by setting fires to drive animals over cliffs. One of the most important uses of fire is for cooking, which kills bacteria and parasites that may be in the food and also makes most food easier to digest. Cooking also makes meat tastier, as chimpanzees have shown by their preference for cooked meat. Fire can also be used to smoke meat, thereby allowing the meat to be stored. In one experiment, mice raised on cooked meat gained 29 percent more weight than those raised on raw meat, suggesting that cooking would have had substantial nutritional benefits for Homo erectus. The nutritional advantage of cooked food may have been one reason why the brain of Homo erectus became much larger than its ancestors. Cooking would have also promoted social interaction when early hominins gathered around campfires to share food.5
The larger brains of Homo erectus enabled them to extend their horizons not only behaviorally but also geographically. Prior to 1.7 million years ago, there is no evidence that any hominin had left the African continent. Between 1.7 million and 700,000 years ago, in what was a remarkable migration, Homo erectus spread halfway around the world, from present-day Spain, France, Germany, Italy, England, Israel, and Georgia to Vietnam, China, and Indonesia. In the latter two countries, Homo erectus fossils were initially known as “Peking Man” and “Java Man.” The fact that Homo erectus could migrate thousands of miles and successfully survive in such varied climates testifies to this hominin’s ability to adapt and cooperate in group endeavors. Since many of the areas where Homo erectus settled were colder than Africa, the use of animal skins as clothing and the control of fire would have been imperative. Cooperative living is also suggested by archeological remains in natural shelters, such as caves, and in the building of artificial shelters. Cooperative hunting and cooperative living both would have required some form of communication, but the degree of language development that existed at that time remains the subject of spirited debate.6
SELF-AWARENESS
Cognitively and behaviorally, the achievements of Homo erectus were remarkable. In the first four million years after separating from other primates, early hominins had only managed to make crude stone tools. Then, in the next million years, they made sophisticated handaxes, carved wooden spears with which they hunted large mammals, controlled the use of fire, and migrated from Africa to settle from England to Indonesia. Evidence of cooperative living and hunting also suggests fundamental changes in hominin relationships. As Canadian psychologist Merlin Donald noted, “With this species, a major threshold had been crossed in human evolution.”7
What is the possible explanation for these extraordinary changes in behavior? Since the size of hominin brains was significantly increasing at the same time these behavioral changes were occurring, it is reasonable to assume the two developments were related. Clearly Homo erectus was much more intelligent than Homo habilis, but can intelligence alone explain the behavioral changes? The changes in interpersonal relationships exhibited by Homo erectus, as exemplified by cooperative hunting and living, suggest that something more had occurred.
A logical place to look for evidence of what might have occurred is in child development. As noted previously, it is generally accepted that the sequence in which children acquire cognitive capacities roughly parallels the sequence in which these capacities developed in human evolution. Human infants acquire increasing motor skills and intelligen
ce for their first two years, at which time they acquire a major cognitive skill—self-awareness. Prior to that age, a child has minimal self-awareness and will often react to its image in a mirror as if it is the image of another child, trying to touch it or crawling around the mirror to find the other child.8
The classic experiment to demonstrate the development of self-awareness in children was done by Beulah Amsterdam at the University of North Carolina in the mid-1960s as part of her psychology dissertation. She put each of eighty-eight children, ages three months to twenty-four months, in front of a mirror, then pointed to the mirror and said, “See, who’s that?” Each child had had a red mark placed on its nose to facilitate self-recognition, and self-recognition was assumed to occur if the child touched its nose or examined it in the mirror. No child younger than eighteen months showed self-recognition, and very few between the ages of eighteen and twenty months did. However, two-thirds of the children between twenty and twenty-four months showed self-recognition. This is also the developmental stage at which children start using personal pronouns such as “me” and “mine” and speak of themselves, as in “I throw ball.” These are indicators of emerging self-awareness.9
It should be emphasized that the development of self-awareness in children is a gradual process. It develops in a series of stages and in the earliest stages may fluctuate from week to week. Its development is not dependent on achieving a specific chronological age but rather on achieving a critical level of brain development, which may vary widely among children. This is illustrated by the fact that most children with autism or Down syndrome develop mirror self-recognition but do so at a later age than other children. Similarly, it would be expected that self-awareness in Homo erectus would have developed slowly and would have fluctuated in its early stages.10
What precisely is self-awareness? Bud Craig, a neuroanatomist at Arizona State University, defined self-awareness as “knowing that I exist” and “the feeling that ‘I am.’ ” Others have called it “the sense of one’s own being,” “the ability to become the object of your own attention,” “the material me,” and “the sentient self.” Craig also noted that “an organism must be able to experience its own existence as a sentient being before it can experience the existence and salience of anything else in the environment.” Evolutionarily, self-awareness probably developed to provide “updated maps of the body’s state … necessary for the brain to regulate life,” and it would have been advantageous insofar as it allowed hominins to integrate their physical and mental states. Self-awareness is also a prerequisite for most higher thought processes; without an “I” there can be no “you.” As Gordon Gallup, a psychologist at the University of Albany, correctly noted, Descartes’s dictum should be revised from “I think, therefore I am” to “I am, therefore I think.”11
How might self-awareness have been beneficial to Homo erectus? By developing an awareness of self, Homo erectus would have developed a crude awareness of others and thus been able to initiate simple cooperative endeavors. Such an awareness of others would probably not have included a detailed understanding of others’ thinking, such as will be described in the following chapter under “theory of mind.” Rather, the awareness would have been more like that found in animals that hunt jointly, such as wolves, lions, baboons, or chimpanzees, or in three- year-old children playing in a sandbox. They are aware of one another without necessarily understanding what the other is thinking. And they are able to cooperate in simple joint undertakings, such as moving all the sand from the sandbox to the grass. Using their self-awareness, Homo erectus could have similarly carried out some cooperative tasks, such as keeping a fire going all night or hunting cooperatively. It is, in fact, difficult to imagine Homo erectus having migrated across the world and surviving, often in cold climates, for hundreds of thousands of years without having been self-aware.
Self-awareness seems so natural to us that it is difficult to imagine hominins who did not possess it. However, some people with brain dysfunction never develop it, while others develop it but then later lose it. Among those who never develop it are some children with congenital rubella or other forms of severe retardation; in one study, many of the severely retarded children were unable to recognize themselves in a mirror at any age, even if given practice sessions.12
Among adults, self-awareness may become impaired with some brain diseases. Some individuals with schizophrenia, for example, have an impaired awareness of self called depersonalization. Such patients have been noted to make statements such as the following: “I’m here but not here”; “I am almost nonexistent”; “I have no consciousness”; and “My feeling of consciousness is fragmented.” In some individuals with Alzheimer’s disease or other forms of dementia, self-awareness may be lost entirely. In one study, seven of 22 patients with moderately severe, and all six patients with very severe, Alzheimer’s disease had lost their ability to recognize themselves in mirrors. Such individuals may even “converse with the person in the mirror and might try to open the door to which the mirror was attached to invite the person in.” In one study, a woman with brain atrophy believed that another woman “who was identical to her in appearance, age, background, education, and so on” lived in her house. She regularly talked to the other woman in the mirror. In another case, a woman with brain atrophy who believed another woman was living in her house “had on occasion thrown a bucket of water and other solid objects at her mirror image to try and persuade it to leave the house.” Such cases illustrate the importance of normal brain functioning for this critical cognitive skill.13
Despite its importance in human cognitive development, self-awareness is not unique to humans. At about the same time that Beulah Amsterdam was using mirrors to assess self-awareness in children, Gordon Gallup was assessing it in various primates. This idea had also occurred to Charles Darwin, who, “while visiting a zoo,… held a mirror up to an orangutan and carefully observed the ape’s reaction, which made a series of facial expressions.” The majority of Gallop’s chimpanzees learned to use a mirror to explore body areas they could not see without the mirror, such as their teeth, ears, and anogenital region. Gallup also used lipstick or marking pens to put red marks on the animals’ faces and ears, and some chimpanzees responded by touching those areas. By contrast, at least thirteen species of monkeys tested have shown no signs of self-recognition. Gallup noted this “decisive difference between monkeys and chimps” and concluded that “the capacity for self-recognition may not extend below man and the great apes.”14
Since Gallup’s initial experiments, self-recognition has been demonstrated in chimpanzees on multiple occasions, as well as in bonobos, in orangutans, and, only rarely, in gorillas. Other indications of self-awareness have also been noted in these animals. For example, an orangutan raised by humans and taught to use sign language spontaneously referred to itself as “me.” Chimpanzees have also learned to recognize themselves in photographs. One chimpanzee who had been raised by humans indicated that it believed it was also a human by assigning its own picture to the human category. When it later was confronted by other live chimpanzees, it referred to them in sign language as “black bugs.”15
The demonstration of mirror self-recognition in chimpanzees and other higher primates raises the question of whether it exists in any other animals. Attempts to demonstrate it in multiple species of fish and birds have all failed except for one experiment with a magpie, a member of the crow family. Among mammals, cats and dogs do not appear to be capable of mirror self-recognition, but elephants, dolphins, and some whales do. A study of three Asian elephants demonstrated clear self-recognition; one elephant even used its trunk to explore a white mark painted on its forehead. Asian elephants are known to be unusually intelligent and can be taught to respond to over one hundred different commands. Through the use of underwater mirrors, dolphins have also been observed to explore parts of their bodies that had been marked. The researchers who did the dolphin study concluded that “the emergence of self
-recognition is not a by-product of factors specific to great apes and humans but instead may be attributable to more general characteristics such as a high degree of encephalization [brain development] and cognitive ability” found in all of the big-brained animals.16
The experiments with mirror self-recognition in primates and other animals illustrate several points. First, all of the animals except humans quickly lose interest in mirror self-recognition. The bottlenose dolphins, for example, were said to show great interest at the beginning, “but like the chimpanzees and unlike young (as well as older) humans, they rapidly lost interest in the procedure.” The elephants also “lost interest quickly.” Second, the experiments confirm the observations in children that self-awareness is strongly age-dependent and that there is significant variation among individuals. Some mature chimpanzees, for example, showed no interest in the mirrors. The experiments have also shown that self-recognition may be inconsistent over time; for example, one orangutan exhibited mirror self-recognition between eighteen and twenty-four months of age but not between twenty-eight and forty-two months of age. The experiments also confirm that mirror self-recognition in primates is restricted to those most closely related to humans. Numerous attempts to demonstrate it in various species of monkeys have uniformly failed; some monkeys appear to regard their mirror image as familiar, but not as self. Finally, the presence of self-awareness in great apes and hominins but not in monkeys suggests that it may have evolved separately in both species instead of having been inherited from an earlier common ancestor.17
Evolving Brains, Emerging Gods Page 5
