Authors: Carl Sagan
The brain does much more than recollect. It compares, synthesizes, analyzes, generates abstractions. We must figure out much more than our genes can know. That is why the brain library is some ten thousand times larger than the gene library. Our passion for learning, evident in the behavior of every toddler, is the tool
for our survival. Emotions and ritualized behavior patterns are built deeply into us. They are part of our humanity. But they are not
characteristically
human. Many other animals have feelings. What distinguishes our species is thought. The cerebral cortex is a liberation. We need no longer be trapped in the genetically inherited behavior patterns of lizards and baboons. We are, each of us, largely responsible for what gets put into our brains, for what, as adults, we wind up caring for and knowing about. No longer at the mercy of the reptile brain, we can change ourselves.
Most of the world’s great cities have grown haphazardly, little by little, in response to the needs of the moment; very rarely is a city planned for the remote future. The evolution of a city is like the evolution of the brain: it develops from a small center and slowly grows and changes, leaving many old parts still functioning. There is no way for evolution to rip out the ancient interior of the brain because of its imperfections and replace it with something of more modern manufacture. The brain must function during the renovation. That is why our brainstem is surrounded by the R-complex, then the limbic system and finally the cerebral cortex. The old parts are in charge of too many fundamental functions for them to be replaced altogether. So they wheeze along, out-of-date and sometimes counterproductive, but a necessary consequence of our evolution.
In New York City, the arrangement of many of the major streets dates to the seventeenth century, the stock exchange to the eighteenth century, the waterworks to the nineteenth, the electrical power system to the twentieth. The arrangement might be more efficient if all civic systems were constructed in parallel and replaced periodically (which is why disastrous fires—the great conflagrations of London and Chicago, for example—are sometimes an aid in city planning). But the slow accretion of new functions permits the city to work more or less continuously through the centuries. In the seventeenth century you traveled between Brooklyn and Manhattan across the East River by ferry. In the nineteenth century, the technology became available to construct a suspension bridge across the river. It was built precisely at the site of the ferry terminal, both because the city owned the land and because major thoroughfares were already converging on the pre-existing ferry service. Later when it was possible to construct a tunnel under the river, it too was built in the same place for the same reasons, and also because small abandoned precursors of tunnels, called caissons, had already been emplaced during the construction
of the bridge. This use and restructuring of previous systems for new purposes is very much like the pattern of biological evolution.
When our genes could not store all the information necessary for survival, we slowly invented them. But then the time came, perhaps ten thousand years ago, when we needed to know more than could conveniently be contained in brains. So we learned to stockpile enormous quantities of information outside our bodies. We are the only species on the planet, so far as we know, to have invented a communal memory stored neither in our genes nor in our brains. The warehouse of that memory is called the library.
A book is made from a tree. It is an assemblage of flat, flexible parts (still called “leaves”) imprinted with dark pigmented squiggles. One glance at it and you hear the voice of another person—perhaps someone dead for thousands of years. Across the millennia, the author is speaking, clearly and silently, inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding together people, citizens of distant epochs, who never knew one another. Books break the shackles of time, proof that humans can work magic.
Some of the earliest authors wrote on clay. Cuneiform writing, the remote ancestor of the Western alphabet, was invented in the Near East about 5,000 years ago. Its purpose was to keep records: the purchase of grain, the sale of land, the triumphs of the king, the statutes of the priests, the positions of the stars, the prayers to the gods. For thousands of years, writing was chiseled into clay and stone, scratched onto wax or bark or leather; painted on bamboo or papyrus or silk—but always one copy at a time and, except for the inscriptions on monuments, always for a tiny readership. Then in China between the second and sixth centuries, paper, ink and printing with carved wooden blocks were all invented, permitting many copies of a work to be made and distributed. It took a thousand years for the idea to catch on in remote and backward Europe. Then, suddenly, books were being printed all over the world. Just before the invention of movable type, around 1450, there were no more than a few tens of thousands of books in all of Europe, all handwritten; about as many as in China in 100
B.C
., and a tenth as many as in the Great Library of Alexandria. Fifty years later, around 1500, there were ten million printed books. Learning had become available to anyone who could read. Magic was everywhere.
More recently, books, especially paperbacks, have been printed in massive and inexpensive editions. For the price of a modest meal you can ponder the decline and fall of the Roman Empire,
the origin of species, the interpretation of dreams, the nature of things. Books are like seeds. They can lie dormant for centuries and then flower in the most unpromising soil.
The great libraries of the world contain millions of volumes, the equivalent of about 10
14
bits of information in words, and perhaps 10
15
bits in pictures. This is ten thousand times more information than in our genes, and about ten times more than in our brains. If I finish a book a week, I will read only a few thousand books in my lifetime, about a tenth of a percent of the contents of the greatest libraries of our time. The trick is to know which books to read. The information in books is not preprogrammed at birth but constantly changed, amended by events, adapted to the world. It is now twenty-three centuries since the founding of the Alexandrian Library. If there were no books, no written records, think how prodigious a time twenty-three centuries would be. With four generations per century, twenty-three centuries occupies almost a hundred generations of human beings. If information could be passed on merely by word of mouth, how little we should know of our past, how slow would be our progress! Everything would depend on what ancient findings we had accidentally been told about, and how accurate the account was. Past information might be revered, but in successive retellings it would become progressively more muddled and eventually lost. Books permit us to voyage through time, to tap the wisdom of our ancestors. The library connects us with the insights and knowledge, painfully extracted from Nature, of the greatest minds that ever were, with the best teachers, drawn from the entire planet and from all of our history, to instruct us without tiring, and to inspire us to make our own contribution to the collective knowledge of the human species. Public libraries depend on voluntary contributions. I think the health of our civilization, the depth of our awareness about the underpinnings of our culture and our concern for the future can all be tested by how well we support our libraries.
Were the Earth to be started over again with all its physical features identical, it is extremely unlikely that anything closely resembling a human being would ever again emerge. There is a powerful random character to the evolutionary process. A cosmic ray striking a different gene, producing a different mutation, can have small consequences early but profound consequences late. Happenstance may play a powerful role in biology, as it does in history. The farther back the critical events occur, the more powerfully can they influence the present.
For example, consider our hands. We have five fingers, including one opposable thumb. They serve us quite well. But I think we would be served equally well with six fingers including a thumb, or four fingers including a thumb, or maybe five fingers and two thumbs. There is nothing intrinsically best about our particular configuration of fingers, which we ordinarily think of as so natural and inevitable. We have five fingers because we have descended from a Devonian fish that had five phalanges or bones in its fins. Had we descended from a fish with four or six phalanges, we would have four or six fingers on each hand and would think them perfectly natural. We use base ten arithmetic only because we have ten fingers on our hands.
*
Had the arrangement been otherwise, we would use base eight or base twelve arithmetic and relegate base ten to the New Math. The same point applies, I believe, to many more essential aspects of our being—our hereditary material, our internal biochemistry, our form, stature, organ systems, loves and hates, passions and despairs, tenderness and aggression, even our analytical processes—all of these are, at least in part, the result of apparently minor accidents in our immensely long evolutionary history. Perhaps if one less dragonfly had drowned in the Carboniferous swamps, the intelligent organisms on our planet today would have feathers and teach their young in rookeries. The pattern of evolutionary causality is a web of astonishing complexity; the incompleteness of our understanding humbles us.
Just sixty-five million years ago our ancestors were the most unprepossessing of mammals—creatures with the size and intelligence of moles or tree shrews. It would have taken a very audacious biologist to guess that such animals would eventually produce the line that dominates the Earth today. The Earth then was full of awesome, nightmarish lizards—the dinosaurs, immensely successful creatures, which filled virtually every ecological niche. There were swimming reptiles, flying reptiles, and reptiles—some as tall as a six-story building—thundering across the face of the Earth. Some of them had rather large brains, an upright posture and two little front legs very much like hands, which they used to catch small, speedy mammals—probably including our distant ancestors—for dinner. If such dinosaurs had survived, perhaps the dominant intelligent species on our planet today would be four meters tall with green skin and sharp teeth, and the human form would be considered a lurid fantasy of saurian
science fiction. But the dinosaurs did not survive. In one catastrophic event all of them and many, perhaps most, of the other species on the Earth, were destroyed.
*
But not the tree shrews. Not the mammals. They survived.
No one knows what wiped out the dinosaurs. One evocative idea is that it was a cosmic catastrophe, the explosion of a nearby star—a supernova like the one that produced the Crab Nebula. If there were by chance a supernova within ten or twenty light-years of the solar system some sixty-five million years ago, it would have sprayed an intense flux of cosmic rays into space, and some of these, entering the Earth’s envelope of air, would have burned the atmospheric nitrogen. The oxides of nitrogen thus generated would have removed the protective layer of ozone from the atmosphere, increasing the flux of solar ultraviolet radiation at the surface and frying and mutating the many organisms imperfectly protected against intense ultraviolet light. Some of those organisms may have been staples of the dinosaur diet.
The disaster, whatever it was, that cleared the dinosaurs from the world stage removed the pressure on the mammals. Our ancestors no longer had to live in the shadow of voracious reptiles. We diversified exuberantly and flourished. Twenty million years ago, our immediate ancestors probably still lived in the trees, later descending because the forests receded during a major ice age and were replaced by grassy savannahs. It is not much good to be supremely adapted to life in the trees if there are very few trees. Many arboreal primates must have vanished with the forests. A few eked out a precarious existence on the ground and survived. And one of those lines evolved to become us. No one knows the cause of that climatic change. It may have been a small variation in the intrinsic luminosity of the Sun or in the orbit of the Earth; or massive volcanic eruptions injecting fine dust into the stratosphere, reflecting more sunlight back into space and cooling the Earth. It may have been due to changes in the general circulation of the oceans. Or perhaps the passage of the Sun through a galactic dust cloud. Whatever the cause, we see again how tied our existence is to random astronomical and geological events.
After we came down from the trees, we evolved an upright posture; our hands were free; we possessed excellent binocular vision—we had acquired many of the preconditions for making
tools. There was now a real advantage in possessing a large brain and in communicating complex thoughts. Other things being equal, it is better to be smart than to be stupid. Intelligent beings can solve problems better, live longer and leave more offspring; until the invention of nuclear weapons, intelligence powerfully aided survival. In our history it was some horde of furry little mammals who hid from the dinosaurs, colonized the treetops and later scampered down to domesticate fire, invent writing, construct observatories and launch space vehicles. If things had been a little different, it might have been some other creature whose intelligence and manipulative ability would have led to comparable accomplishments. Perhaps the smart bipedal dinosaurs, or the raccoons, or the otters, or the squid. It would be nice to know how different other intelligences can be; so we study the whales and the great apes. To learn a little about what other kinds of civilizations are possible, we can study history and cultural anthropology. But we are all of us—us whales, us apes, us people—too closely related. As long as our inquiries are limited to one or two evolutionary lines on a single planet, we will remain forever ignorant of the possible range and brilliance of other intelligences and other civilizations.
On another planet, with a different sequence of random processes to make hereditary diversity and a different environment to select particular combinations of genes, the chances of finding beings who are physically very similar to us is, I believe, near zero. The chances of finding another form of intelligence is not. Their brains may well have evolved from the inside out. They may have switching elements analogous to our neurons. But the neurons may be very different; perhaps superconductors that work at very low temperatures rather than organic devices that work at room temperature, in which case their speed of thought will be 10
7
times faster than ours. Or perhaps the equivalent of neurons elsewhere would not be in direct physical contact but in radio communication so that a single intelligent being could be distributed among many different organisms, or even many different planets, each with a part of the intelligence of the whole, each contributing by radio to an intelligence much greater than itself.
*
There may be planets where the intelligent beings have about 10
14
neural connections, as we do. But there may be places where the number is 10
24
or 10
34
. I wonder what they would know. Because
we inhabit the same universe as they, we and they must share some substantial information in common. If we could make contact, there is much in their brains that would be of great interest to ours. But the opposite is also true. I think extraterrestrial intelligence—even beings substantially further evolved than we—will be interested in us, in what we know, how we think, what our brains are like, the course of our evolution, the prospects for our future.