by Carl Sagan
Paul Broca died in 1880, perhaps of the very sort of aneurism that he had studied so brilliantly. At the moment of his death he was working on a comprehensive study of brain anatomy. He had established the first professional societies, schools of research, and scientific journals of modern anthropology in France. His laboratory specimens became incorporated into what for many years was called the Musée Broca. Later it merged to become a part of the Musée de l’Homme.
It was Broca himself, whose brain I was cradling, who had established the macabre collection I had been contemplating. He had studied embryos and apes, and people of all races, measuring like mad in an effort to understand the nature of a human being. And despite the present appearance of the collection and my suspicions, he was not, at least by the standards of his time, more of a jingoist or a racist than most, and certainly not that standby of fiction and, more rarely, of fact: the cold, uncaring, dispassionate scientist, heedless of the human consequences of what he does. Broca very much cared.
In the Revue d’Anthropologie of 1880 there is a complete bibliography of Broca’s writings. From the titles I could later glimpse something of the origins of the collection I had viewed: “On the Cranium and Brain of the Assassin Lemaire,” “Presentation of the Brain of a Male Adult Gorilla,” “On the Brain of the Assassin Prévost,” “On the Supposed Heredity of Accidental Characteristics,” “The Intelligence of Animals and the Rule of Humans,” “The Order of the Primates: Anatomical Parallels between Men and Apes,” “The Origin of the Art of Making Fire,” “On Double Monsters,” “Discussion on Microcephalics,” “Prehistoric Trepanning,” “On Two Cases of a Supernumerary Digit Developing at an Adult Age,” “The Heads of Two New Caledonians” and “On the Skull of Dante Alighieri.” I did not know the present resting place of the cranium of the author of The Divine Comedy, but the collection of brains and skulls and heads that surrounded me clearly began in the work of Paul Broca.
BROCA WAS a superb brain anatomist and made important investigations of the limbic region, earlier called the rhinencephalon (the “smell brain”), which we now know to be profoundly involved in human emotion. But Broca is today perhaps best known for his discovery of a small region in the third convolution of the left frontal lobe of the cerebral cortex, a region now known as Broca’s area. Articulate speech, it turns out, as Broca inferred on only fragmentary evidence, is to an important extent localized in and controlled by Broca’s area. It was one of the first discoveries of a separation of function between the left and right hemispheres of the brain. But most important, it was one of the first indications that specific brain functions exist in particular locales in the brain, that there is a connection between the anatomy of the brain and what the brain does, an activity sometimes described as “mind.”
Ralph Holloway is a physical anthropologist at Columbia University whose laboratory I imagine must bear some resemblance to Broca’s. Holloway makes rubber-latex casts of the insides of skulls of human and related beings, past and present, to attempt a reconstruction, from slight impressions on the interior of the cranium, of what the brain must have been like. Holloway believes that he can tell from a creature’s cranium whether Broca’s area is present, and he has found evidence of an emerging Broca’s area in the brain of Homo habilis some two million years ago-just the time of the first constructions and the first tools. To this limited extent there is something to the phrenological vision. It is very plausible that human thought and industry went hand in hand with the development of articulate speech, and Broca’s area may in a very real sense be one of the seats of our humanity, as well as a means for tracing our relationships with our ancestors on their way toward humanity.
And here was Broca’s brain floating, in formalin and in fragments, before me. I could make out the limbic region which Broca had studied in others. I could see the convolutions on the neocortex. I could even make out the gray-white left frontal lobe in which Broca’s own Broca’s area resided, decaying and unnoticed, in a musty corner of a collection that Broca had himself begun.
It was difficult to hold Broca’s brain without wondering whether in some sense Broca was still in there-his wit, his skeptical mien, his abrupt gesticulations when he talked, his quiet and sentimental moments. Might there be preserved in the configuration of neurons before me a recollection of the triumphant moment when he argued before the combined medical faculties (and his father, overflowing with pride) on the origins of aphasia? A dinner with his friend Victor Hugo? A stroll on a moonlit autumn evening, his wife holding a pretty parasol, along the Quai Voltaire and the Pont Royal? Where do we go when we die? Is Paul Broca still there in his formalin-filled bottle? Perhaps the memory traces have decayed, although there is good evidence from modern brain investigations that a given memory is redundantly stored in many different places in the brain. Might it be possible at some future time, when neurophysiology has advanced substantially, to reconstruct the memories or insights of someone long dead? And would that be a good thing? It would be the ultimate breach of privacy. But it would also be a kind of practical immortality, because, especially for a man like Broca, our minds are clearly a major aspect of who we are.
From the character of this neglected storeroom in the Musée de l’Homme I had been ready to attribute to those who had assembled the collection-I had not known it was Broca at the time-a palpable sexism and racism and jingoism, a profound resistance to the idea of the relatedness of human beings and the other primates. And in part it was true. Broca was a humanist of the nineteenth century, but unable to shake the consuming prejudices, the human social diseases, of his time. He thought men superior to women, and whites superior to blacks. Even his conclusion that German brains were not significantly different from French ones was in rebuttal to a Teutonic claim of Gallic inferiority. But he concluded that there were deep connections in brain physiology between gorillas and men. Broca, the founder of a society of freethinkers in his youth, believed in the importance of untrammeled inquiry and had lived his life in pursuit of that aim. His falling short of these ideals shows that someone as unstinting in the free pursuit of knowledge as Broca could still be deflected by endemic and respectable bigotry. Society corrupts the best of us. It is a little unfair, I think, to criticize a person for not sharing the enlightenment of a later epoch, but it is also profoundly saddening that such prejudices were so extremely pervasive. The question raises nagging uncertainties about which of the conventional truths of our own age will be considered unforgivable bigotry by the next. One way to repay Paul Broca for this lesson which he has inadvertently provided us is to challenge, deeply and seriously, our own most strongly held beliefs.
These forgotten jars and their grisly contents had been collected, at least partly, in a humanistic spirit; and perhaps, in some era of future advance in brain studies, they would prove useful once again. I would be interested in knowing a little more about the redmustachioed man who had been, in part, returned to France from New Caledonia.
But the surroundings, the sense of a chamber of horrors, evoked unbidden other unsettling thoughts. At the very least, we feel in such a place a pang of sympathy for those-especially those who died young or in pain-who are in so unseemly a way thus memorialized. Cannibals in northwestern New Guinea employ stacked skulls for doorposts, and sometimes for lintels. Perhaps these are the most convenient building materials available, but the architects cannot be entirely unaware of the terror that their constructions evoke in unsuspecting passers-by. Skulls have been used by Hitler’s SS, Hell’s Angels, shamans, pirates, and even those who label bottles of iodine, in a conscious effort to elicit terror. And it makes perfectly good sense. If I find myself in a room filled with skulls, it is likely that there is someone nearby, perhaps a pack of hyenas, perhaps some gaunt and dedicated decapitator, whose occupation or hobby it is to collect skulls. Such fellows are almost certainly to be avoided, or, if possible, killed. The prickle of the hairs on the back of my neck, the increased heartbeat and pulse rate, that strange, cl
ammy feeling are designed by evolution to make me fight or flee. Those who avoid decapitation leave more offspring. Experiencing such fears bestows an evolutionary advantage. Finding yourself in a room full of brains is still more horrifying, as if some unspeakable moral monster, armed with ghastly blades and scooping tools, were shuffling and drooling somewhere in the attics of the Musée de l’Homme.
But all depends, I think, on the purpose of the collection. If its objective is to find out, if it has acquired human parts post mortem-especially with the prior consent of those to whom the parts once belonged-then little harm has been done, and perhaps in the long run some significant human good. But I am not sure the scientists are entirely free of the motives of those New Guinea cannibals; are they not at least saying, “I live with these heads every day. They don’t bother me. Why should you be so squeamish?”?
LEONARDO AND VESALIUS were reduced to bribery and stealth in order to perform the first systematic dissections of human beings in Europe, although there had been a flourishing and competent school of anatomy in ancient Greece. The first person to locate, on the basis of neuroanatomy, human intelligence in the head was Herophilus of Chalcedon, who flourished around 300 B.C. He was also the first to distinguish the motor from the sensory nerves, and performed the most thorough study of brain anatomy attempted until the Renaissance. Undoubtedly there were those who objected to his gruesome experimental predilections. There is a lurking fear, made explicit in the Faust legend, that some things are not “meant” to be known, that some inquiries are too dangerous for human beings to make. And in our own age, the development of nuclear weapons may, if we are unlucky or unwise, turn out to be a case of precisely this sort. But in the case of experiments on the brain, our fears are less intellectual. They run deeper into our evolutionary past. They call up images of the wild boars and highwaymen who would terrorize travelers and rural populations in ancient Greece, by Procrustean mutilation or other savagery, until some hero-Theseus or Hercules-would effortlessly dispatch them. These fears have served an adaptive and useful function in the past. But I believe they are mostly emotional baggage in the present. I was interested, as a scientist who has written about the brain, to find such revulsions hiding in me, to be revealed for my inspection in Broca’s collection. These fears are worth fighting.
All inquiries carry with them some element of risk. There is no guarantee that the universe will conform to our predispositions. But I do not see how we can deal with the universe-both the outside and the inside universe-without studying it. The best way to avoid abuses is for the populace in general to be scientifically literate, to understand the implications of such investigations. In exchange for freedom of inquiry, scientists are obliged to explain their work. If science is considered a closed priesthood, too difficult and arcane for the average person to understand, the dangers of abuse are greater. But if science is a topic of general interest and concern-if both its delights and its social consequences are discussed regularly and competently in the schools, the press, and at the dinner table-we have greatly improved our prospects for learning how the world really is and for improving both it and us. That is an idea, I sometimes fancy, that may be sitting there still, sluggish with formalin, in Broca’s brain.
CHAPTER 2
CAN WE KNOW THE UNIVERSE?
REFLECTIONS ON A GRAIN OF SALT
Nothing is rich but the inexhaustible wealth
of nature. She shows us only surfaces,
but she is a million fathoms deep.
RALPH WALDO EMERSON
SCIENCE IS A WAY of thinking much more than it is a body of knowledge. Its goal is to find out how the world works, to seek what regularities there may be, to penetrate to the connections of things-from subnuclear particles, which may be the constituents of all matter, to living organisms, the human social community, and thence to the cosmos as a whole. Our intuition is by no means an infallible guide. Our perceptions may be distorted by training and prejudice or merely because of the limitations of our sense organs, which, of course, perceive directly but a small fraction of the phenomena of the world. Even so straightforward a question as whether in the absence of friction a pound of lead falls faster than a gram of fluff was answered incorrectly by Aristotle and almost everyone else before the time of Galileo. Science is based on experiment, on a willingness to challenge old dogma, on an openness to see the universe as it really is. Accordingly, science sometimes requires courage-at the very least the courage to question the conventional wisdom.
Beyond this the main trick of science is to really think of something: the shape of clouds and their occasional sharp bottom edges at the same altitude everywhere in the sky; the formation of a dewdrop on a leaf; the origin of a name or a word-Shakespeare, say, or “philanthropic”; the reason for human social customs-the incest taboo, for example; how it is that a lens in sunlight can make paper burn; how a “walking stick” got to look so much like a twig; why the Moon seems to follow us as we walk; what prevents us from digging a hole down to the center of the Earth; what the definition is of “down” on a spherical Earth; how it is possible for the body to convert yesterday’s lunch into today’s muscle and sinew; or how far is up-does the universe go on forever, or if it does not, is there any meaning to the question of what lies on the other side? Some of these questions are pretty easy. Others, especially the last, are mysteries to which no one even today knows the answer. They are natural questions to ask. Every culture has posed such questions in one way or another. Almost always the proposed answers are in the nature of “Just So Stories,” attempted explanations divorced from experiment, or even from careful comparative observations.
But the scientific cast of mind examines the world critically as if many alternative worlds might exist, as if other things might be here which are not. Then we are forced to ask why what we see is present and not something else. Why are the Sun and the Moon and the planets spheres? Why not pyramids, or cubes, or dodecahedra? Why not irregular, jumbly shapes? Why so symmetrical, worlds? If you spend any time spinning hypotheses, checking to see whether they make sense, whether they conform to what else we know, thinking of tests you can pose to substantiate or deflate your hypotheses, you will find yourself doing science. And as you come to practice this habit of thought more and more you will get better and better at it. To penetrate into the heart of the thing-even a little thing, a blade of grass, as Walt Whitman said-is to experience a kind of exhilaration that, it may be, only human beings of all the beings on this planet can feel. We are an intelligent species and the use of our intelligence quite properly gives us pleasure. In this respect the brain is like a muscle. When we think well, we feel good. Understanding is a kind of ecstasy.
But to what extent can we really know the universe around us? Sometimes this question is posed by people who hope the answer will be in the negative, who are fearful of a universe in which everything might one day be known. And sometimes we hear pronouncements from scientists who confidently state that everything worth knowing will soon be known-or even is already known-and who paint pictures of a Dionysian or Polynesian age in which the zest for intellectual discovery has withered, to be replaced by a kind of subdued languor, the lotus eaters drinking fermented coconut milk or some other mild hallucinogen. In addition to maligning both the Polynesians, who were intrepid explorers (and whose brief respite in paradise is now sadly ending), as well as the inducements to intellectual discovery provided by some hallucinogens, this contention turns out to be trivially mistaken.
Let us approach a much more modest question: not whether we can know the universe or the Milky Way Galaxy or a star or a world. Can we know, ultimately and in detail, a grain of salt? Consider one microgram of table salt, a speck just barely large enough for someone with keen eyesight to make out without a microscope. In that grain of salt there are about 1016 sodium and chlorine atoms. This is a 1 followed by 16 zeros, 10 million billion atoms. If we wish to know a grain of salt, we must know at least the three-dimensional positio
ns of each of these atoms. (In fact, there is much more to be known-for example, the nature of the forces between the atoms-but we are making only a modest calculation.) Now, is this number more or less than the number of things which the brain can know?
How much can the brain know? There are perhaps 1011 neurons in the brain, the circuit elements and switches that are responsible in their electrical and chemical activity for the functioning of our minds. A typical brain neuron has perhaps a thousand little wires, called dendrites, which connect it with its fellows. If, as seems likely, every bit of information in the brain corresponds to one of these connections, the total number of things knowable by the brain is no more than 1014, one hundred trillion. But this number is only one percent of the number of atoms in our speck of salt.
So in this sense the universe is intractable, astonishingly immune to any human attempt at full knowledge. We cannot on this level understand a grain of salt, much less the universe.
But let us look a little more deeply at our microgram of salt. Salt happens to be a crystal in which, except for defects in the structure of the crystal lattice, the position of every sodium and chlorine atom is predetermined. If we could shrink ourselves into this crystalline world, we would see rank upon rank of atoms in an ordered array, a regularly alternating structure-sodium, chlorine, sodium, chlorine, specifying the sheet of atoms we are standing on and all the sheets above us and below us. An absolutely pure crystal of salt could have the position of every atom specified by something like 10 bits of information. [1] This would not strain the information-carrying capacity of the brain.