by Carl Sagan
The limited inventory of symbolic cries among non-human primates seems to be controlled by the limbic system; at least the full vocal repertoire of squirrel and rhesus monkeys can be evoked by electrical stimulation in the limbic system. Human language is controlled in the neocortex. Thus an essential step in human evolution must have been the transfer of control of vocal language from the limbic system to the temporal lobes of the neocortex, a transition from instinctual to learned communication. However, the surprising ability of apes to acquire gestural language and the hint of lateralization in the chimpanzee brain suggest that the acquisition of voluntary symbolic language by primates is not a recent invention. Rather, it goes back many millions of years, consistent with the evidence from endocranial casts for Broca’s area in Homo habilis.
Lesions in the monkey brain of the neocortical areas responsible for speech in humans fail to impair their instinctual vocalizations. The development of human language must therefore involve an essentially new brain system and not merely a reworking of the machinery for limbic cries and calls. Some experts in human evolution have suggested that the acquisition of language occurred very late—perhaps only in the last few tens of thousands of years—and was connected with the challenges of the last ice age. But the data do not seem to be consistent with this view; moreover, the speech centers of the human brain are so complex that it is very difficult to imagine their evolution in the thousand or so generations since the peak of the most recent glaciation.
The evidence suggests that in our ancestors of some tens of millions of years ago there was a neocortex, but one in which the left and right hemispheres served comparable and redundant functions. Since then, upright posture, the use of tools, and the development of language have mutually advanced one another, a small increment in language ability, for example, permitting the incremental improvement of hand axes, and vice versa. The corresponding brain evolution seems to have proceeded by specializing one of the two hemispheres for analytic thinking.
The original redundancy, by the way, represents prudent computer design. For example, with no knowledge of the neuroanatomy of the cerebral cortex, the engineers who designed the on-board memory of the Viking lander inserted two identical computers, which are identically programmed. But because of their complexity, differences between the computers soon emerged. Before landing on Mars the computers were given an intelligence test (by a smarter computer back on Earth). The dumber brain was then turned off. Perhaps human evolution has proceeded in a similar manner and our highly prized rational and analytical abilities are localized in the “other” brain—the one that was not fully competent to do intuitive thinking. Evolution often uses this strategy. Indeed, the standard evolutionary practice of increasing the amount of genetic information as organisms increase in complexity is accomplished by doubling part of the genetic material and then allowing the slow specialization of function of the redundant set.
Almost without exception all human languages have built into them a polarity, a veer to the right. “Right” is associated with legality, correct behavior, high moral principles, firmness, and masculinity; “left,” with weakness, cowardice, diffuseness of purpose, evil, and femininity. In English, for example, we have “rectitude,” “rectify,” “righteous,” “right-hand man,” “dexterity,” “adroit” (from the French “à droite”), “rights,” as in “the rights of man,” and the phrase “in his right mind.” Even “ambidextrous” means, ultimately, two right hands.
On the other side (literally), we have “sinister” (almost exactly the Latin word for “left”), “gauche” (precisely the French word for “left”), “gawky,” “gawk,” and “left-handed compliment.” The Russian “nalevo” for “left” also means “surreptitious.” The Italian “mancino” for “left” signifies “deceitful.” There is no “Bill of Lefts.”
In one etymology, “left” comes from “lyft,” the Anglo-Saxon for weak or worthless. “Right” in the legal sense (as an action in accord with the rules of society) and “right” in the logical sense (as the opposite of erroneous) are also commonplaces in many languages. The political use of right and left seems to date from the moment when a significant lay political force arose as counterpoise to the nobility. The nobles were placed on the king’s right and the radical upstarts—the capitalists—on his left. The nobles were to the royal right, of course, because the king himself was a noble; and his right side was the favored position. And in theology as in politics: “At the right hand of God.”
Many examples of a connection between “right” and “straight” can be found.* In Mexican Spanish you indicate straight (ahead) by saying “right right”; in Black American English, “right on” is an expression of approval, often for a sentiment eloquently or deftly phrased. “Straight” meaning conventional, correct or proper is a commonplace in colloquial English today. In Russian, right is “pravo,” a cognate of “pravda,” which means “true.” And in many languages “true” has the additional meaning of “straight” or “accurate,” as in “his aim was true.”
The Stanford-Binet IQ test makes some effort to examine both left- and right-hemisphere function. For right-hemisphere function there are tests in which the subject is asked to predict the opened configuration of a piece of paper after it is folded several times and a small piece cut out with a pair of scissors; or to estimate the total number of blocks in a stack when some blocks are hidden from view. Although the devisers of the Stanford-Binet test consider such questions of geometric conception to be very useful in determining the “intelligence” of children, they are said to be increasingly less useful in IQ tests of teenagers and adults. There is certainly little room on such examinations for testing intuitive leaps. Unsurprisingly, IQ tests also seem to be powerfully biased toward the left hemisphere.
The vehemence of the prejudices in favor of the left hemisphere and the right hand reminds me of a war in which the side that barely won renames the contending parties and issues, so that future generations will have no difficulty in deciding where prudent loyalty should lie. When Lenin’s party was a fairly small splinter group in Russian socialism he named it the Bolshevik party, which in Russian means the majority party. The opposition obligingly, and with awesome stupidity, accepted the designation of Mensheviks, the minority party. In a decade and a half they were. Similarly, in the worldwide associations of the words “right” and “left” there is evidence of a rancorous conflict early in the history of mankind.* What could arouse such powerful emotions?
In combat with weapons which cut or stab—and in such sports as boxing, baseball and tennis—a participant trained in the use of the right hand will find himself at a disadvantage when confronted unexpectedly with a left-hander. Also, a malevolent left-handed swordsman might be able to come quite close to his adversary with his unencumbered right hand appearing as a gesture of disarmament and peace. But these circumstances do not seem to be able to explain the breadth and depth of antipathy to the left hand, nor the extension of right chauvinism to women—traditional noncombatants.
One, perhaps remote, possibility is connected with the unavailability of toilet paper in preindustrial societies. For most of human history, and in many parts of the world today, the empty hand is used for personal hygiene after defecation, a fact of life in pretechnological cultures. It does not follow that those who follow this custom enjoy it. Not only is it aesthetically unappealing, it involves a serious risk of transferring disease to others as well as to oneself. The simplest precaution is to greet and to eat with the other hand. Without apparent exception in pretechnological human societies, it is the left hand that is used for such toilet functions and the right for greeting and eating. Occasional lapses from this convention are quite properly viewed with horror. Severe penalties have been visited on small children for breaches of the prevailing handedness conventions; and many older people in the West can still remember a time when there were firm strictures against even reaching for objects with the left hand. I believe this ac
count can explain the virulence against associations with “left” and the defensive self-congratulatory bombast attached to associations with “right” which are commonplace in our right-handed society. The explanation does not, however, explain why the right and left hands were originally chosen for these particular functions. It might be argued that statistically there is one chance in two that toilet functions would be relegated to the left hand. But we would then expect one society in two to be righteous about leftness. In fact, there seem to be no such societies. In a society where most people are right-handed, precision tasks such as eating and fighting would be relegated to the favored hand, leaving by default toilet functions to the side sinister. However, this also does not account for why the society is right-handed. In its most fundamental sense, the explanation must lie elsewhere.
There is no direct connection between the hand you prefer to use for most tasks and the cerebral hemisphere that controls speech, and the majority of left-handers may still have speech centers in the left hemisphere, although this point is in dispute. Nevertheless, the existence of handedness itself is thought to be connected with brain lateralization. Some evidence suggests the left-handers are more likely to have problems with such left-hemisphere functions as reading, writing, speaking and arithmetic; and to be more adept at such right-hemisphere functions as imagination, pattern recognition and general creativity.* Some data suggest that human beings are genetically biased towards right-handedness. For example, the number of ridges on fingerprints of fetuses during the third and fourth months of gestation is larger in the right hand than the left hand, and this preponderance persists throughout fetal life and after birth.
Two robust Australopithecines. These animals may have been predominantly right-handed; the gracile Australopithecines very likely were. Copyright © 1965, 1973 Time, Inc.
Information on the handedness of the Australopithecines has been obtained from an analysis of fossil baboon skulls fractured with bone or wooden clubs by these early relatives of man. The discoverer of the Australopithecine fossils, Raymond Dart, concluded that about 20 percent of them were left-handed, which is roughly the fraction in modern man. In contrast, while other animals often show strong paw preferences, the favored paw is almost as likely to be left as right.
The left/right distinctions run deep into the past of our species. I wonder if some slight whiff of the battle between the rational and the intuitive, between the two hemispheres of the brain, has not surfaced in the polarity between words for right and left: it is the verbal hemisphere that controls the right side. There may not in fact be more dexterity in the right side; but it certainly has a better press. The left hemisphere seems to feel quite defensive—in a strange way insecure—about the right hemisphere; and, if this is so, verbal criticism of intuitive thinking becomes suspect on the ground of motive. Unfortunately, there is every reason to think that the right hemisphere has comparable misgivings—expressed nonverbally, of course—about the left.
Admitting the validity of both methods of thinking, left hemisphere and right hemisphere, we must ask if they are equally effective and useful in new circumstances. There is no doubt that right-hemisphere intuitive thinking may perceive patterns and connections too difficult for the left hemisphere; but it may also detect patterns where none exist. Skeptical and critical thinking is not a hallmark of the right hemisphere. And unalloyed right-hemisphere doctrines, particularly when they are invented during new and trying circumstances, may be erroneous or paranoid.
Recent experiments by Stuart Dimond, a psychologist at University College, Cardiff in Wales, have employed special contact lenses to show films to the right or left hemisphere only. Of course, the information arriving in one hemisphere in a normal subject can be transmitted via the corpus callosum to the other hemisphere. Subjects were asked to rate a variety of films in terms of emotional content. These experiments showed a remarkable tendency for the right hemisphere to view the world as more unpleasant, hostile, and even disgusting than the left hemisphere. The Cardiff psychologists also found that when both hemispheres are working, our emotional responses are very similar to those of the left hemisphere only. The negativism of the right hemisphere is apparently strongly tempered in everyday life by the more easygoing left hemisphere. But a dark and suspicious emotion tone seems to lurk in the right hemisphere, which may explain some of the antipathy felt by our left hemisphere selves to the “sinister” quality of the left hand and the right hemisphere.
In paranoid thinking a person believes he has detected a conspiracy—that is, a hidden (and malevolent) pattern in the behavior of friends, associates or governments—where in fact no such pattern exists. If there is such a conspiracy, the subject may be profoundly anxious, but his thinking is not necessarily paranoid. A famous case involves James Forrestal, the first U.S. Secretary of Defense. At the end of World War II, Forrestal was convinced that Israeli secret agents were following him everywhere. His physicians, equally convinced of the absurdity of this idée fixe, diagnosed him as paranoid and confined him to an upper story of Walter Reed Army Hospital, from which he plunged to his death, partly because of inadequate supervision by hospital personnel, overly deferential to one of his exalted rank. Later it was discovered that Forrestal was indeed being followed by Israeli agents who were worried that he might reach a secret understanding with representatives of Arab nations. Forrestal had other problems, but having his valid perception labeled paranoid did not help his condition.
In times of rapid social change there are bound to be conspiracies, both by those in favor of change and by those defending the status quo, the latter more than the former in recent American political history. Detecting conspiracies when there are no conspiracies is a symptom of paranoia; detecting them when they exist is a sign of mental health. An acquaintance of mine says, “In America today, if you’re not a little paranoid you’re out of your mind.” The remark, however, has global applicability.
There is no way to tell whether the patterns extracted by the right hemisphere are real or imagined without subjecting them to left-hemisphere scrutiny. On the other hand, mere critical thinking, without creative and intuitive insights, without the search for new patterns, is sterile and doomed. To solve complex problems in changing circumstances requires the activity of both cerebral hemispheres: the path to the future lies through the corpus callosum.
An example of different behavior arising from different cognitive functions—one example of many—is the familiar human reaction to the sight of blood. Many of us feel queasy or disgusted or even faint at the sight of copious bleeding in someone else. The reason, I think, is clear. We have over the years associated our own bleeding with pain, injury, and a violation of bodily integrity; and we experience a sympathetic or vicarious agony in seeing someone else bleed. We recognize their pain. This is almost certainly the reason that the color red is used to signify danger or stop* in many diverse human societies. (If the oxygen-carrying pigment in our blood were green—which biochemically it could have been—we would, all of us, think green a quite natural index of danger and be amused at the idea of using red.) A trained physician, on the other hand, has a different set of perceptions when faced with blood. What organ is injured? How copious in the bleeding? Is it venous or arterial flow? Should a tourniquet be applied? These are all analytic functions of the left hemisphere. They require more complex and analytic cognitive processes than the simple association: blood equals pain. And they are far more practical. If I were injured, I would much rather be with a competent physician who through long experience has become almost entirely inured to gore than with an utterly sympathetic friend who faints dead away at the sight of blood. The latter may be highly motivated not to wound another person, but the former will be able to help if such a wound occurs. In an ideally structured species, these two quite different attitudes would be present simultaneously in the same individual. And in most of us that is just what has happened. The two modes of thinking are of very different complexity
, but they have complementary survival value.
A typical example of the occasional resistance mustered by intuitive thinking against the clear conclusions of analytical thinking is D. H. Lawrence’s opinion of the nature of the moon: “It’s no use telling me it’s a dead rock in the sky! I know it’s not.” Indeed, the moon is more than a dead rock in the sky. It is beautiful, it has romantic associations, it raises tides, it may even be the ultimate reason for the timing of the human menstrual cycle. But certainly one of its attributes is that it is a dead rock in the sky. Intuitive thinking does quite well in areas where we have had previous personal or evolutionary experience. But in new areas—such as the nature of celestial objects close up—intuitive reasoning must be diffident in its claims and willing to accommodate to the insights that rational thinking wrests from Nature. By the same token, the processes of rational thought are not ends in themselves but must be perceived in the larger context of human good; the nature and direction of rational and analytical endeavors should be determined in significant part by their ultimate human implications, as revealed through intuitive thinking.
In a way, science might be described as paranoid thinking applied to Nature: we are looking for natural conspiracies, for connections among apparently disparate data. Our objective is to abstract patterns from Nature (right-hemisphere thinking), but many proposed patterns do not in fact correspond to the data. Thus all proposed patterns must be subjected to the sieve of critical analysis (left-hemisphere thinking). The search for patterns without critical analysis, and rigid skepticism without a search for patterns, are the antipodes of incomplete science. The effective pursuit of knowledge requires both functions.
