Asimov's New Guide to Science

by Isaac Asimov

  Of course, Stapp was strapped in the sled in a manner to minimize injury. He suffered only bruises, blisters, and painful eye shocks that produced two black eyes.

  An astronaut, on take-off, must absorb (for a short while) as much as 6½ g and, at re-entry, up to 11 g.

  Devices such as contour couches, harnesses, and perhaps even immersion in water in a water-filled capsule or space suit will give a sufficient margin of safety against high g forces.

  Similar studies and experiments are being made on the radiation hazards, the boredom of long isolation, the strange experience of being in soundless space where night never falls, and other eerie conditions that space fliers will have to endure. All in all, those preparing for humanity’s first venture away from the neighborhood of its home planet see no insurmountable obstacles ahead.

  The psychological difficulties of long space voyages may not, in fact, prove very serious if we do not persist in thinking of the astronauts as Earthpeople. If they are, of course, then there is an enormous difference between their life on the outside of a huge planet and their stay inside a small spaceship.

  What, however, if the explorers are people from space settlements of the type Gerard O’Neill envisions? These settlers will be accustomed to an internal environment, to having their food, drink and air tightly cycled, to having variations in the gravitational effect, to living in a space environment. A spaceship will be a smaller version of the settlement they are used to and have lived in, perhaps, all their lives.

  It may be the space settlers then that will be the cutting edge of human exploration in the twenty-first century and thereafter. It will be they, perhaps, who reach the asteroids. There, mining operations will supply a new level of resources for expanded humanity, and many of the asteroids may be hollowed out as natural settlements, many of them considerably larger than any that would be practical in the Earth-moon system.

  From the asteroids as a base, human beings can explore the vast reaches of the outer solar system… and beyond that lie the stars.

  Chapter 17

  * * *

  The Mind

  The Nervous System

  Physically speaking, we humans are rather unimpressive specimens, as organisms go. We cannot compete in strength with most other animals our size. We walk awkwardly, compared with, say, the cat; we cannot run with the dog or the deer; in vision, hearing, and the sense of smell, we are inferior to a number of other animals. Our skeletons are ill suited to our erect posture: the human is probably the only animal that develops “low back pain” from normal posture and activities. When we think of the evolutionary perfection of other organisms—the beautiful efficiency of the fish for swimming or of the bird for flying, the great fecundity and adaptability of the insects, the perfect simplicity and efficiency of the virus—the human being seems a clumsy and poorly designed creature indeed. As sheer organism, we can scarcely compete with the creatures occupying any specific environmental niche on earth. We have come to dominate the earth only by grace of one rather important specialization—the brain.

  NERVE CELLS

  A cell is sensitive to a change in its surroundings (stimulus) and will react appropriately (response). Thus, a protozoon will swim toward a drop of sugar solution deposited in the water near it, or away from a drop of acid. Now this direct, automatic sort of response is fine for a single cell, but it would mean chaos for a collection of cells. Any organism made up of a number of cells must have a system that coordinates their responses. Without such a system, it would be like a city of people completely out of communication with one another and acting at cross purposes. So even the coelenterates, the most primitive multicelled animals, have the beginnings of a nervous system. We can see in them the first nerve cells (neurons)—special cells with fibers that extend from the main cell body and put out extremely delicate branches (figure 17.1).

  Figure 17.1. A nerve cell.

  The functioning of nerve cells is so subtle and complex that even at this simple level we are already a little beyond our depth when it comes to explaining just what happens. In some way not yet understood, a change in the environment acts upon the nerve cell. It may be a change in the concentration of some substance, or in the temperature, or in the amount of light, or in the movement of the water, or it may be an actual touch by some object. Whatever the stimulus, it sets up a tiny nerve impulse, an electric current that progresses rapidly along the fiber. When it reaches the end of the fiber, the impulse jumps a tiny gap (synapse) to the next nerve cell; and so it is transmitted from cell to cell. (In well-developed nervous systems, a nerve cell may make thousands of synapses with its neighbors.) In the case of a coelenterate, such as a jellyfish, the impulse is communicated throughout the organism. The jellyfish responds by contracting some part or all of its body. If the stimulus is contact with a food particle, the organism engulfs the particle by contraction of its tentacles.

  All this is strictly automatic, of course, but since it helps the jellyfish, we like to read purpose into the organism’s behavior. Indeed, humans, as creatures who behave in a purposeful, motivated way, naturally tend to attribute purpose even to inanimate nature. Scientists call this attitude teleological, and try to avoid such a way of thinking and speaking as much as they can. But in describing the results of evolution, it is so convenient to speak in terms of development toward more efficient ends that even among scientists all but the most fanatical purists occasionally lapse into teleology. (Readers of this book have noticed, of course, that I have sinned often.) Let us, however, try to avoid teleology in considering the development of the nervous system and the brain. Nature did not design the brain; it came about as the result of a long series of evolutionary accidents, so to speak, which happened to produce helpful features that at each stage gave an advantage to organisms possessing them. In the fight for survival, an animal that was more sensitive to changes in the environment than its competitors, and could respond to them faster, would be favored by natural selection. If, for instance, an animal happened to possess some spot on its body that was exceptionally sensitive to light, the advantage would be so great that evolution of eye spots, and eventually of eyes, would follow almost inevitably.

  Specialized groups of cells that amount to rudimentary sense organs begin to appear in the Platyhelminthes, or flatworms. Furthermore, the flatworms also show the beginnings of a nervous system that avoids sending nerve impulses indiscriminately throughout the body, but instead speeds them to the critical points of response. The development that accomplishes this is a central nerve cord. The flatworms are the first to develop a central nervous system.

  This is not all. The flatworm’s sense organs are localized in its head end, the first part of its body that encounters the environment as it moves along, and so naturally the nerve cord is particularly well developed in the head region. That knob of development is the beginning of a brain.

  Gradually the more complex phyla add new features. The sense organs increase in number and sensitivity. The nerve cord and its branches grow more elaborate, developing a widespread system of afferent (“carrying to”) nerve cells that bring messages to the cord and efferent (“carrying away”) fibers that transmit messages to the organs of response. The knot of nerve cells at the crossroads in the head becomes more and more complicated. Nerve fibers evolve into forms that can carry the impulses faster. In the squid, the most highly developed of the unsegmented animals, this faster transmission is accomplished by a thickening of the nerve fiber. In the segmented animals, the fiber develops a sheath of fatty material (myelin) which is even more effective in speeding the nerve impulse. In human beings, some nerve fibers can transmit the impulse at 100 meters per second (about 225 miles per hour), compared with only about 1/10 mile per hour in some of the invertebrates. The chordates introduce a radical change in the location of the nerve cord.

  In them this main nerve trunk (better known as the spinal cord) runs along the back instead of along the belly, as in all lower animals. This may see
m a step backward—putting the cord in a more exposed position. But the vertebrates have the cord well protected within the bony spinal column. The backbone, though its first function was protecting the nerve cord, produced amazing dividends, for it served as a girder upon which chordates could hang bulk and weight. From the backbone they can extend ribs that enclose the chest, jawbones that carry teeth for chewing, and long bones that form limbs.

  BRAIN DEVELOPMENT

  The chordate brain develops from three structures that are already present in simple form in the most primitive vertebrates. These structures, at first mere swellings of nerve tissue, are the forebrain, the midbrain, and the hindbrain, a division first noted by the Greek anatomist Erasistratus of Chios about 280 B.C. At the head end of the spinal cord, the cord widens smoothly into the hindbrain section known as the medulla oblongata. On the front side of this section in all but the most primitive chordates is a bulge called the cerebellum (“little brain”). Forward of this is the midbrain. In the lower vertebrates the midbrain is concerned chiefly with vision and has a pair of optic lobes, while the forebrain is concerned with smell and taste and contains olfactory bulbs. The forebrain, reading from front to rear, is divided into the olfactory-bulb section, the cerebrum, and the thalamus, the lower portion of which is the hypothalamus. (Cerebrum is Latin for “brain”; in humans, at least, the cerebrum is the largest and most important part of the organ.) By removing the cerebrum from animals and observing the results, the French anatomist Marie Jean Pierre Flourens was able to demonstrate in 1824 that it is indeed the cerebrum that is responsible for acts of thought and will. (For the human brain, see figure 17.2.)

  Figure 17.2.The human brain.

  It is the roof of the cerebrum, moreover—the cap called the cerebral cortex—that is the star of the whole show. In fishes and amphibians, this is merely a smooth covering (called the pallium, or “cloak”). In reptiles a patch of new nerve tissue, called the neopallium (“new cloak”) appears. This is the real forerunner of things to come. It will eventually take over the supervision of vision and other sensations. In the reptiles, the clearing house for visual messages has already moved from the midbrain to the forebrain in part; in birds this move is completed. With the first mammals, the neopallium begins to take charge. It spreads virtually over the entire surface of the cerebrum. At first it remains a smooth coat, but as it goes on growing in the higher mammals, it becomes so much larger in area than the surface of the cerebrum that it is bent into folds, or convolutions. This folding is responsible for the complexity and capacity of the brain of a higher mammal, notably that of Homo sapiens.

  More and more, as one follows this line of species development, the cerebrum comes to dominate the brain. The midbrain fades to almost nothing. In the case of the primates, which gain in the sense of sight at the expense of the sense of smell, the olfactory lobes of the forebrain shrink to mere blobs. By this time the cerebrum has expanded over the thalamus and the cerebellum.

  Even the early humanlike fossils had considerably larger brains than the most advanced apes. Whereas the brain of the chimpanzee or of the orangutan weighs less than 400 grams (under 14 ounces), and the gorilla, though far larger than a man, has a brain that averages about 540 grams (19 ounces), Pithecanthropus’s brain apparently weighed about 850 to 1,000 grams (30 to 35 ounces). And these were the small-brained hominids. Rhodesian man’s brain weighed about 1,300 grams (46 ounces); the brain of Neanderthal and of modern Homo sapiens comes to about 1,500 grams (53 ounces or 3.3 pounds). The modern human’s mental gain Over Neanderthal apparently lies in the fact that a larger proportion of the human brain is concentrated in the foreregions, which apparently control the higher aspects of mental function. Neanderthal was a low-brow whose brain bulged in the rear; a human today, in contrast, is a high-brow whose brain bulges in front.

  The hominid brain has about tripled in size in the last 3 million years—a fast increase as evolutionary changes go. But why did that happen? Why the hominids?

  One possible reason is that we now know that even very early, small-brained hominids walked erect, exactly as modern humans do. Erect posture long preceded the enlarged brain. Erect posture has two important consequences: first, the eyes are lifted higher above the ground and deliver more information to the brain; second, the forelimbs are permanently freed so that they might feel and manipulate the environment. The flood of sense perceptions, long-distance sight, and short-distance touch make an enlarged brain capable of dealing with new material useful, and any individuals whose brains happen to be more efficient (through superior size or organization) are bound to have an advantage over others. Evolutionary procedures would then inevitably produce large-brained hominids. (Or so it seems to us in hindsight.)

  THE HUMAN BRAIN

  The modern human brain is about 1/50 of the total human body weight. Each gram of brain weight is in charge, so to speak, of 50 grams of body. In comparison, the chimpanzee’s brain is about 1/150 the weight of its body, and the gorilla’s about 1/500 its body. To be sure, some of the smaller primates have an even higher brain/‌body ratio than human beings do. (So do the hummingbirds.) A marmoset can have a brain that is 1/18 the weight of its body. However, there the mass of the brain is too small in absolute terms for it to be able to pack into itself the necessary complexity for intelligence on the human scale. In short, what is needed, and what humans have, is a brain that is large both in the absolute sense and in relation to body size.

  This is made plain by the fact that two types of mammal have brains that are distinctly larger than the human brain and yet that do not lend those mammals superintelligence. The largest elephants can have brains as massive as 6,000 grams (about 13 pounds) and the largest whales can have brains that reach a mark of 9,000 grams (or nearly 19 pounds). The size of the bodies those brains must deal with is, however, enormous. The elephant’s brain, despite its size, is only 1/1,000 the weight of its body, and the brain of a large whale may be only 1/10,000 the weight of its body.

  In only one direction, however, do humans have a possible rival. The dolphins and porpoises, small members of the whale family, show possibilities. Some of these are no heavier than a person and yet have brains that are larger (with weights up to 1,700 grams, or 60 ounces) and more extensively convoluted.

  It is not safe to conclude from this evidence alone that the dolphin is more intelligent than we are, because there is the question of the internal organization of the brain. The dolphin’s brain (like that of Neanderthal man) may be oriented more in the direction of what we might consider lower functions.

  The only safe way to tell is to attempt to gauge the intelligence of the dolphin by actual experiment. Some investigators, notably John C. Lilly, seem convinced that dolphin intelligence is indeed comparable to our own, that dolphins and porpoises have a speech pattern as complicated as ours, and that possibly a form of interspecies communication may yet be established.

  Even if this is so, there can be no question but that dolphins, however intelligent, lost their opportunity to translate that intelligence into control of the environment when they readapted to sea life. It is impossible to make use of fire under water, and it was the discovery of the use of fire that first marked off hominids from all other organisms. More fundamentally still, rapid locomotion through a medium as viscous as water requires a thoroughly streamlined shape. This has made impossible in the dolphin the development of anything equivalent to the human arm and hand with which the environment can be delicately investigated and manipulated.

  Another interesting point is that human beings caught up and surpassed the cetaceans. When hominids were still small-brained, the dolphins were already large-brained, yet the latter could not stop the former. It would seem inconceivable to us today that we would allow the evolutionary development of a large-brained rat, or even a large-brained dog to threaten our position on Earth, but the dolphins, trapped at sea, could do nothing to prevent hominid development to the point where we now can wipe out cetacean li
fe with scarcely an effort, if we wish. (It is to our credit that so many of us do not wish and are making every effort to prevent it.)

  The dolphins may, in some philosophical manner we do not yet understand, surpass us in some forms of intelligence, but as far as effective control of the environment and the development of technology are concerned, Homo sapiens stands without a peer on Earth at present or, as far as we know, in the past. (It goes without saying that the activity of human beings in exercising their intelligence and technological capacity has not necessarily always been for the good of the planet—or for themselves, for that matter.)

  INTELLIGENCE TESTING

  While considering the difficulty in determining the precise intelligence level of a species such as the dolphin, it might be well to say that no completely satisfactory method exists for measuring the precise intelligence level of individual members of our own species.

  In 1904, the French psychologists Alfred Binet and Theodore Simon devised means of testing intelligence by answers given to judiciously chosen questions. Such intelligence tests give rise to the expression intelligence quotient (or I.Q.), representing the ratio of the mental age, as measured by the test, to the chronological age—this ratio being multiplied by 100 to remove decimals. The public was made aware of the significance of I.Q. chiefly through the work of the American psychologist Lewis Madison Terman.