Evolving Brains, Emerging Gods
Page 6
Finally, the experiments demonstrate that the self-awareness existing in nonhuman primates is at a comparatively early stage of development; according to the researchers, it is said to not go “beyond incipient forms equivalent to those of 2- or 3-year-old children.” As noted by evolutionary biologist Ian Tattersall of the American Museum of Natural History, “Apes exploit their images in mirrors far less comprehensively than children do.… Apes make no attempt to modify their images, even in ways that might make them more socially successful.” This point was wittily conveyed by British physician and philosopher Raymond Tallis, who believes that the significance of chimpanzee self-recognition has been “grossly exaggerated.” In regard to the use of lipstick to make marks on the chimpanzee’s face, Tallis noted “that the chimpanzee did not buy the lipstick, agonize over the colour, wonder whether it would match her clothes or be in tune with current fashion, hope it would excite her partner or shock her parents, nor did she ring her friend or colour consultant for advice.”18
THE BRAIN OF HOMO ERECTUS
Given the significant increase in brain size of Homo erectus, did self-awareness emerge at this stage of hominin development because they had a larger brain, consistent with its emergence in apes, elephants, and dolphins? It is a reasonable guess, especially since such self-awareness would have facilitated many of the behaviors exhibited by Homo erectus. Self-awareness confers an ability to think about oneself, including one’s needs, at more than an instinctual level as well as one’s reactions to others.
What do we know about the brain of Homo erectus, in addition to the fact that it was much larger than its predecessors? According to those who have studied Homo erectus skulls, their brains had “intriguing similarities to the modern human brain.” Specifically, “the chief exterior landmarks of brain anatomy are all there: the Rolandic and Sylvian fissures, the large temporal and frontal lobes, the expanded parietal lobe, and the enlarged cerebellum.” In addition, the two sides of the brain are not equal, an indication of the lateralization of functions that would become a hallmark of human brains. Based on studies of stone tools made by Homo erectus, there is also a “pronounced right-hand preference of their makers.”19
Although self-awareness undoubtedly involves many brain areas, recent human neuroimaging studies have identified three areas that appear to be critical parts of the brain’s self-awareness network: the anterior cingulate, anterior insula, and inferior parietal lobule, as shown in figure 2.1. The anterior cingulate (BA 24, 32) lies in the medial prefrontal cortex. Although it is anatomically part of an older brain area, the anterior cingulate appears to have been evolutionarily remodeled to become functionally part of the much newer prefrontal cortex. The anterior cingulate has many functions. The insula (which does not have a BA number) lies directly behind the underside of the prefrontal cortex and is among the most recently evolved brain areas; some researchers have claimed that it has no equivalent area in monkeys. The inferior parietal area (BA 39, 40) is also one of the most recently evolved brain areas, as mentioned in the preceding chapter.20
Given the massive increase in the brain size of Homo erectus, it seems probable that white matter connecting tracts would also have been increasing in complexity. The superior longitudinal fasciculus, described in the previous chapter, includes connections to the anterior cingulate, insula, and inferior parietal area and thus plays an important role in self-awareness. Another connecting tract that may have become more prominent at this time is the uncinate fasciculus, which connects the insula to other frontal lobe areas and to the temporal lobe, including the amygdala, which is important for the expression of emotions. Studies of the evolution of white matter connecting tracts have identified the uncinate fasciculus as one of the two most recently developed white matter tracts, consistent with its role in facilitating self-awareness.21
FIGURE 2.1 Homo erectus: an aware self.
Although the anterior cingulate, insula, and inferior parietal area are known to have multiple functions, the one function they share is self-awareness. The fact that the anterior cingulate is part of this network should come as no surprise; more than a century ago, it was suggested “that the fundamental role of [the] prefrontal cortex was self-awareness or consciousness of self.” Similarly, the insula is said to be “uniquely involved in interoception, the awareness of the body’s internal state” and “self-awareness.” Neuroimaging studies in which people’s brains are monitored as they view pictures of themselves have shown activation of the anterior cingulate and the anterior insula, especially on the right side. A summary of these studies suggested that these brain areas contain “the anatomical substrate for the evolved capacity of humans to be aware of themselves.” Damage to these two areas, as occurs in some cases of dementia, results in “a selective loss of self-conscious behavior and a loss of emotional awareness of self and others.”22
The inferior parietal lobule complements the anterior cingulate and anterior insula in overseeing an awareness of self but also functions to monitor a person’s body parts and their relationship to one another. This skill would have enabled Homo erectus to manipulate its hands more precisely in, for example, the task of making better tools and weapons. As described by Karl Zilles: “The maintenance of a spatial reference for goal-directed movements seems to be a major function of the posterior [inferior] parietal region. This function is a prerequisite for important human activities (i.e., tool use and conceptualization of actions).”23
Multiple human neuroimaging studies have confirmed the contribution of the inferior parietal lobule to the brain network governing bodily self-awareness. This brain area, often in conjunction with the prefrontal cortex, also becomes activated when individuals are asked to do things such as describe their own personality, recognize pictures of themselves, or imagine themselves doing various activities. For example, when healthy volunteers were shown pictures of themselves, the “medial frontal and inferior parietal lobes,” among other areas, were activated. Similarly, a neuroimaging study of eight individuals who were experiencing feelings of depersonalization (“feel detached from their physical selves”) reported that the inferior parietal lobule was among the areas activated. Other studies have reported activation of the anterior cingulate in similar cases.24
A SELF-AWARE NEURON?
Perhaps the most intriguing aspect of the development of self-awareness in hominins is the possibility that self-awareness may be the product of a particular type of brain cell that arose in the course of recent evolution. These cells are commonly referred to as von Economo neurons, or VENs, after an Austrian neurologist, Constantin von Economo, who described them in 1926. VENs are approximately four times larger than regular neurons, have a distinctive spindle shape, and are sometimes referred to as “spindle neurons.” They appear shortly before birth in humans, then slowly stabilize in number during the first four years of life, eventually constituting 1 or 2 percent of the total neurons in the brain areas in which they are found. Thus, the VENs are thought to be “a phylogenetically recent specialization in human evolution.”25
The distribution of VENS in the human brain and in other animals corresponds remarkably closely to the brain areas associated with self-awareness. VENs have even been called “the neurons which make us human.” Thus, in humans, VENs have been found primarily in the anterior cingulate and anterior insula. They have also been reported to occur in much smaller numbers in the lateral prefrontal cortex but not in five other brain areas that have been examined. Among primates, VENs have been found in smaller numbers than in humans in the brains of bonobos, chimpanzees, gorillas, and orangutans, all of which have demonstrated mirror self-awareness. They have also been found in macaque monkeys, which have not demonstrated self-awareness, but not in 23 other species of monkeys, which also have not. Among nonprimate species, VENs have been described in the brains of elephants and dolphins, both of which have shown mirror self-awareness, and in whales, which have not been tested for self-awareness, but not in 30 other nonpri
mate species.26
Additional support for the importance of VENs in facilitating self-awareness comes from studies of frontotemporal dementia, a disease that begins in a person’s fifties or sixties. The major symptoms of frontotemporal dementia are “a reduction in self-monitoring, self-awareness, and the ability to place the self in a social context.” Thus, in the early stages of the disease individuals “behave inappropriately and with disregard for social rules,… have trouble comprehending other people’s perspective … [and] have difficulty with self-awareness, showing an inability to recognize even dramatic changes in their own personality.” In contrast to people with early Alzheimer’s disease, the memory of individuals with frontotemporal dementia is relatively intact. Studies that have been done on the brains of individuals with frontotemporal dementia following death have reported “severe, selective and early loss of VENs,” with a 74 percent reduction of these neurons in the anterior cingulate and insula.27
Our understanding of VENs is still in the early stages. Since they occur mostly in mammals with large brains and in brain areas associated with self-awareness, it seems possible that VENs evolved to solve some problems related to having a large brain. One theory suggests that VENs transmit information faster than do common pyramidal neurons, making the larger brains more efficient. Thus, self-awareness, the second major cognitive leap forward, may have been one consequence of this evolutionary development.28
In summary, around 1.8 million years ago a new hominin, Homo erectus, emerged. It had a much larger brain and exhibited more sophisticated behavior than its predecessors. In addition to being more intelligent, it is likely that Homo erectus was also self-aware. Like Narcissus, Homo erectus would have been able to admire its own reflection in a still pool. With intelligence and self-awareness, Homo erectus had taken two of the cognitive steps necessary to become a fully modern Homo sapiens, able to contemplate its place in the universe and its relationship to the gods. However, it was not yet fully aware of what other hominins were thinking, or introspectively able to think about its own thinking. It was also unable to integrate time past and time present into a fully planned future. Endowed with both intelligence and self-awareness, hominins were ready to take the next cognitive step forward, one that in retrospect seems almost inevitable.
3
ARCHAIC HOMO SAPIENS (NEANDERTALS)
An Empathic Self
A man, to be greatly good,… must put himself in the place of another and of many others; the pains and pleasures of his species must become his own.
—Percy Bysshe Shelley, “A Defence of Poetry,” 1821
In terms of longevity, Homo erectus was the most successful hominin species that ever inhabited this planet, surviving for approximately 15 times longer than our own species has so far survived. Given its success and broad geographical distribution, it is not surprising that at least 700,000 years ago, Homo erectus began evolving into several other hominin species, commonly grouped together and designated as Archaic Homo sapiens. Some members of this hominin group apparently developed a new major cognitive advance that would be essential for ultimately becoming modern Homo sapiens and for understanding the gods.
Depending on where they lived geographically, these hominins have been given various names, such as Homo heidelbergensis and Homo neanderthalensis (Neandertals) for those in Europe. Some specimens from Spain, dated to approximately 430,000 years ago, display features of both of these. Those in Africa are called Homo rhodesiensis, and recently another species has also been found there. In Indonesia a well-publicized group has been designated as Homo floresiensis and in Siberia as Denisovans. The Denisovans were genetically “a sister group to Neandertals,” whom they apparently outnumbered and with whom they interbred. We also know that Denisovans interbred with modern Homo sapiens after the latter left Africa and moved eastward 60,000 years ago, since Denisovan DNA has been found in the genomes of present-day Melanesians, Australian aborigines, and natives of Papua New Guinea but not in the genomes of people living elsewhere. There were almost certainly other Archaic Homo sapiens species that have yet to be discovered.1
The best-known species of Archaic Homo sapiens is the Neandertals, both because they lived in Europe, where the majority of archeological research has been carried out, and because they have been immortalized by the Flintstones. They lived from approximately 230,000 to 40,000 years ago. The largest concentration of Neandertals lived in what is now southern France, but they were widely, if sparsely, distributed from Wales in the west to Uzbekistan and southern Siberia in the east. There is no evidence that Neandertals ever migrated to China or Indonesia, as their Homo erectus ancestors had done, or that they ever lived in Africa. Studies of Neandertal DNA suggest that their total population was relatively small.2
The most striking physical characteristic of the Neandertals was their large brain, which averaged 1,480 cubic centimeters, thus being larger than the average 1,350 cubic centimeters of modern humans. Homo erectus had achieved an average brain capacity of 1,000 cubic centimeters by 1.5 million years ago, but thereafter it increased little. However, after Neandertals evolved from Homo erectus, the Neandertal brain capacity increased dramatically. As Stanford University anthropologist Richard Klein noted, Archaic Homo sapiens “had achieved modern or near-modern brain size by 200,000 years ago.”3
Neandertals averaged about five feet, five inches in height and weighed approximately 185 pounds, thus being significantly larger than Homo erectus. They had powerful upper-body musculature, and their short, stocky frames, similar to modern-day Eskimos, would have been advantageous in the cold European climate. They followed animal herds in the summer and spent winters in a home base, often a cave. Because Europe was colder than it is today, they must have made extensive use of fire and animal skins for warmth.4
The Neandertals were excellent hunters. They made stone tools, bone tools, and weapons that were significantly more sophisticated than those made by Homo erectus. In making stone tools, for example, they replaced the handaxe technique, which had been used for almost one million years, with the Levallois technique, in which flakes of predetermined size and shape were detached from a stone surface; this technique apparently developed independently in Africa and southwest Asia. Their spears, however, were “the high point of known Neandertal innovation.” They were said to be “as elegantly balanced as Olympic javelins” and were used to hunt herd animals, the source of their largely protein diet. Much of the hunting was done in groups, and there is evidence of coordinated actions, such as driving herds of bison and mammoths over a cliff. They also caught fish and birds.5
Despite having large brains and sophisticated hunting techniques, the culture of the Neandertals is widely regarded as having been remarkably static. According to University of California anthropologist Brian Fagan, “There were no innovations, just a narrow repertoire of ancient technologies that sustained them for thousands of years.” They never invented the harpoon, bow and arrow, or other weapons, despite hunting large animals for almost 200,000 years. Based on their brain size alone, Neandertals should have built computers and flown to the moon. The discrepancy between their brain size and lifestyle has puzzled archeologists and was characterized by British linguist Derek Bickerton as a “brain-culture mismatch.… The overriding impression of the technological evidence in the archeological record is one of almost unimaginable monotony.”6
In recent years, some researchers have questioned whether the culture of the Neandertals was as static as has been traditionally portrayed. It has been claimed that Neandertals were using ochre, which can be used for body decoration, as early as 200,000 years ago. However, ochre can be used in a variety of ways, including as an insect repellant, for tanning skins, and for hafting stone tools onto wooden handles, so finding ochre does not necessarily mean that it was being used for decoration. There have also been two reports of ochre-stained marine shells, dated to 45,000 to 50,000 years ago, in caves thought to have been occupied by Neandertals in Italy and Sp
ain. There is also evidence that Neandertals collected the wing bones of large birds such as eagles, falcons, and swans, as well as the talons of eagles. Some researchers have suggested that they did so in order to collect the feathers to be used as decorations, although the bones and talons may have also been collected to be used as some kind of tool. Finally, there is one report of crosshatched lines, at least 39,000 years old, carved on to a rock in a cave on Gibraltar thought to have been occupied by Neandertals. Such findings have reinvigorated the ongoing and unresolved debate regarding the cognitive abilities of Neandertals.7
It seems certain that Neandertals did differ from their hominin predecessors in one important respect. For the first time in history, there are suggestions that some hominins exhibited caring behavior toward other members of their group. The evidence comes from caves in Spain and Iraq. In the latter, the remains of nine Neandertals, estimated to have died 60,000 to 80,000 years ago, were found. One older man showed evidence of having had severe injuries with multiple fractures that occurred many years before his death. His injuries included trauma to his right arm and leg that would have crippled him as well as a blow to his head that likely left him blind in one eye. Such a hominin would not have survived for long on his own, suggesting that fellow Neandertals provided care for him for many years. Studies have shown that other Neandertals “suffered terribly from arthritis or had lost limbs.” In order to have survived, “others in the group must have shared food with them and helped them move from camp to camp, clear evidence of pity and affection.”8