The medical profession insists that the use of drugs to substitute for the output of the thymus organ and the pineal gland, or to stimulate their renewed activity, or even to reduce the number of free radicals in the body, is a total waste of time and money. The general public, on the other hand, often seems to agree with the student who answered the question on an English test, "What is a word for an ignorant pretender to medical knowledge?" with "A doctor."
At any rate, there is current widespread interest in such nonprescription drugs as melatonin, Co-enzyme Q, Vitamin C, Vitamin E, Vitamin B-6, Vitamin B-12, DHEA (de-hydro-epi-androsterone), and SAM (S-adenosyl-methionine). In less than ten years we will have evidence as to whether these diet additives have any beneficial effect on the aging process. Meanwhile, many people are not waiting. The drugs may be no more than stopgap measures, retarding aging but certainly not halting or reversing it; but, the logic goes, that's a good deal better than nothing.
One other whole-body function seems to correlate with aging. The first signs that we are beginning to age appear when our bodies stop growing. Moreover, animals such as carp, which grow continuously, also seem to live indefinitely long. They die only when some disease or predator disposes of them.
Continuous growth hardly appears an answer for humans. I doubt if anyone wants to be twelve feet tall and fifteen hundred pounds, unable to move or even to stand up. But might there be some "growth extract" that we could take from animals, to increase our own life expectancy?
I'm not optimistic. In any case, the science fiction story using that idea was written long ago. In Aldous Huxley's book After Many a Summer Dies the Swan (Huxley, 1939), an eccentric old oil magnate adopts the unpleasant diet of "triturated carp viscera"—chopped-up carp guts. He lives to be over two hundred years old, but at a price. Like Tithonus, who asked the gods only for immortality, he does not die but continues to age. As he does so he goes through a process of devolution, by the end of the story becoming an ape.
I'm not sure any of us want that. On the other hand, for another century or more of life . . . maybe just a trial taste?
6.7 Tissue engineering. It is a great annoyance when the "dumb beasts" of the animal world do things that we supposedly super-smart humans cannot; not just things based on specialization of body structure, such as flying like an eagle, swimming like a dolphin, or jumping like a flea, but things which by all logic our bodies should be able to manage without modification.
Why can't we hibernate or estivate, slowing our metabolism in times when food or water is short? Surely that was once a valuable survival mechanism, even if food for many of us is now almost too easily available. Still of importance today, why can't we grow a new finger or foot if we lose one, or connect a spinal cord severed by injury? We grow new skin without any problem, so some regeneration capability is clearly built into us. But amphibians can grow whole new limbs, which means they also have the capacity to regenerate nerve cells.
If we cannot regrow a limb or an organ, you might think that we ought at least to be able to accept one from some other human donor. The heart is nothing more than a pump, and one person's pancreas is in all important details exactly like another's. Livers, spleens, testicles or ovaries, hearts, wombs, lungs and kidneys are functionally identical in you and in me. It seems reasonable that you should be able to take one of my kidneys if yours are failing.
As the first surgeons to attempt organ transplants quickly learned, it's not so easy. The operation is relatively straightforward, but unless the donor happens to be your identical twin there is a big danger of organ rejection. The body treats the new part not as an essential and helpful component of itself, but as an intruder.
The problem lies not at the organ level, but at the cell level. Our bodies, as part of their defense mechanisms against invading organisms, seek out and destroy anything that does not carry the correct chemical markers that denote "self." The body functions that perform such recognition, and label something as "friend" (ignore) or "foe" (destroy), are known collectively as the immune system. Identical twins have the same immune system, and transplants between such twins are not rejected. Lacking an identical twin, your chances of a successful transplant are best if your organ donor is a close relative.
Today, organ transplants are usually accompanied by drugs that inhibit the action of the immune system. That, of course, carries its own risk. What happens when the bacteria of disease enter your body after a transplant operation? Without your immune system to recognize and devour the intruders, bacteria will multiply freely. You will die—not from organ rejection, but from some conventional infection.
Transplant patients live on the fine edge between two dangers. Too many immune system inhibitors, and infection gets you; too few, and the new organ is rejected by the body. When the immune system is weakened, it is vital to recognize the signs of disease and use antibiotics and other drugs to fight it in its earliest stages.
Is there a way out?
There is, but it is not yet a standard part of the medical community's arsenal. It is known as tissue engineering.
The basic idea is simple. Suppose that one of your body organs is failing. To be specific, let us suppose that it is your kidney. Even a diseased kidney has healthy cells. If we could just take a few of those cells, and encourage them to divide and multiply in the right way (including making structural components of the kidney, such as veins and arteries), then we could grow a whole kidney outside your body. When we performed the transplant, the new kidney would be in no danger of rejection. The immune system would identify the replacement organ as "self."
Unfortunately we cannot grow a kidney in vitro, using some nutrient bath; and if we try to grow a copy of one of your kidneys in some other person or animal, the host's immune system will send up the red flag that denotes "enemy," and proceed to destroy the intruder cells before they can begin the task of kidney construction. Again, we seem to be stymied.
However, occasionally an item appears in the news about a "bubble child." This is a person who has been born without a working immune system. The only way this unfortunate can survive is by complete isolation from all people and diseases. It is a precarious existence, and the fact that such a person could in principle accept any organ transplant without rejection is little consolation.
What nature occasionally does to humans, scientists have been able to do with animals. Lines of mice and rats have been bred that lack immune systems. They will not reject foreign tissue introduced into their bodies. Suppose that we introduce under the skin of such an animal a mold of porous, biodegradable polymer, configured to match the shape and structure of a kidney. We "seed" this mold with cells from your own kidney. These cells will be nourished by the blood of the host mouse or rat. They will multiply, to produce a whole kidney as the biodegradable "scaffolding" dissolves away. There will finally be a whole kidney, ready for removal and use as a replacement for your own failing kidney.
That is the idea. The execution, to make any organ we choose, is years in the future. At the moment there has been success only with the growth of cartilage. The other organs mentioned represent a far tougher problem.
There is also the problem that a mouse or rat is much too small to support the growth of a human liver weighing three pounds or more. In addition, some people would certainly find such a use of animals inhumane and unacceptable.
My own preferred solution to both problems is simple. The one living organism in the world whose immune system is guaranteed not to reject my tissue is me. When tissue engineering is perfected, I will grow copies of my own heart, lungs, and other necessary organs, on or in my own body, in advance of need. When full-grown they will be removed from me and placed in cold storage until the time comes to use them.
As a final note, let us recognize that for some diseases organ replacement will never be an option. This is the case with anything affecting the brain. Alone of all our organs, the brain contains our sense of identity. Another approach can then sometimes
be used. Fetal tissue has not yet developed its own characteristic signature for immune system recognition. Thus, implanted fetal tissue is less likely to suffer rejection by the host body. Parkinson's disease is characterized by a loss of dopamine production. The implanting of fetal dopamine-producing tissue in a patient's brain alleviates the worst symptoms of the disease.
The most effective such tissue is human fetal tissue. The treatment does not, of course, produce a cure. It also leads, in an aggravated form, to ethical questions similar to those arising whenever animals or humans become a part of human medical procedures.
A discussion of other ethical questions and possible societal response to tissue engineering can be found in a novel by Nancy Kress, Maximum Light (Kress, 1998).
CHAPTER 7
New Worlds for Old
The solar system has provided a wonderful, fertile field for speculation since the earliest days of science fiction. Set your stories there, by all means; but unless you want those stories to be dismissed as fantasy by the critical reader, make it the new solar system, as revealed by recent observations.
Even fifty years ago, the writer had lots of freedom. Telescopic observations of the Sun, Moon, and planets had told us a fair amount, but that was overwhelmed by the things we didn't know—what does the other side of the Moon, never seen from Earth, look like? What is beneath the perennial clouds of Venus?
Today, those and many other mysteries have gone away. Planetary probes have had a close-up look at every world except Pluto. Space-based telescopes have given us not only images, but spectroscopic data about all the planets.
We will confine this chapter to the "edges" of the solar system—not in terms of location, but in terms of knowledge. We will seek virgin territory for storytelling, where there is still hope for surprises.
7.1 Mercury. The planet closest to the Sun is Mercury. Before 1974, this was thought of as an airless ball, moving around the Sun in a rather elongated ellipse every 88 days. It was believed to present the same face to the Sun all the time, so that one side would be fiercely hot, and the other chillingly cold. Astronomers knew that Mercury had little or no atmosphere. A planet closer to the Sun than Earth sometimes passes between us and the Sun. Sunlight will then be refracted by any substantial atmosphere. There is no sign of that, so the surface of Mercury must be close to a perfect vacuum.
The big change in our knowledge of Mercury came with the Mariner 10 spacecraft, which in 1974-75 performed a series of flybys of the planet. It sent back pictures from three close encounters, and produced the first big surprise: the surface of Mercury looks at first sight exactly like the Moon. It is cratered, barren, and airless. Mariner also discovered a magnetic field, about one percent of Earth's. This, together with the planet's high density, suggests a substantial iron core maybe 1,500 kilometers in diameter. (Mercury itself is only 4,500 kms. in diameter.) At least part of that core should be fluid, allowing the existence of a permanent dynamo that generates the external magnetic field.
Mercury's rotation period was another surprise. The old assumption, that tidal forces would have locked it in position to present the same face to the Sun all the time, turned out to be wrong. If that were the case, the rotation period of Mercury would be the same as its year, 88 days. Mercury actually goes through one complete revolution on its axis in 58.6 Earth-days. It is no coincidence that 58.6 is two-thirds of 88. A dynamical effect known as a "resonance lock" keeps those two periods in that exact ratio. As one odd result, a day on Mercury lasts exactly two of its years (because the planet turns one and a half times on its axis in the time it takes to make one full circuit around the Sun). Since the planet does not present the same face to the Sun all the time, all sides get baked; the planet is hot all over, except possibly at the very poles, rather than just on one side as was previously thought.
Mercury has probably changed little in appearance in the past three billion years. However, it has one interesting difference from the Moon; its surface is more wrinkled, probably as a result of more cooling and contraction than the Moon has ever experienced. On the other hand, anything three billion years old has a right to be wrinkled.
The "old" Mercury allowed some fascinating science fiction stories to be written about it. The modern Mercury is rather dull—or should we say, a good challenge to the writer's imagination?
7.2 Venus. If Mercury was for a long time something of a mystery to astronomers, Venus was a positive embarrassment. Galileo, back in 1610, took a look at the Planet of Love with his homemade telescope and noted that the surface seemed completely featureless. That, improvements in telescopes and observing techniques notwithstanding, was the way that Venus obstinately remained for the next three and a half centuries. Venus was known to be about the same size as the Earth—a "sister planet," as people were fond of saying, coming closer to Earth than any other, and only a few hundred kilometers smaller in radius (6,050, to Earth's 6,370). But if this were our sister, we knew remarkably little about her. The length of the Venus year was determined, but not the day; and the surface was a complete and total mystery, because of the all-pervading and eternal cloud layer.
Naturally, that absence of facts did not stop people from speculating. One popular notion was of Venus as a younger and more primitive form of Earth—probably hotter, and perhaps entirely covered with oceans. The logic was simple: hotter, because nearer the Sun; and clouds meant water, so more clouds than Earth meant more water. Venus might be a steamy, swampy planet, where it rained and rained and rained.
There were competing theories. Fred Hoyle, the astronomer whom we met in Chapter 2 and will meet again in Chapter 13, speculated that Venus indeed had oceans; but according to his theory they would be oceans of hydrocarbons (the ultimate answer to a fossil fuel crisis).
Hoyle's ideas sound wild, but at least they were based on an extrapolation of known physical laws. Whereas Immanuel Velikovsky, in the early 1950s, came up with the wildest, least scientific—and most popular—theory of all. Venus, he said, was once part of Jupiter. By some unspecified event it was ripped out of the Jovian system and proceeded inward. There, after a complicated game of celestial billiards with Mars and the Earth, it settled down to become Venus in its present orbit. And all this took place not at the dawn of creation of the solar system, but recently, 3,500 years ago. Among other things, the multiple passages of Venus past the Earth stopped our planet in its rotation, caused a universal deluge (the Flood), parted the Red Sea, and caused numerous other annoyances.
Read Velikovsky, by all means, for wild ideas—but don't believe him. We will mention just one problem with the theory, that it violates the law of conservation of angular momentum, and leave it at that.
In the past thirty years, space probes have dramatically changed our knowledge and understanding of Venus. The present description runs as follows:
* The period for Venus to make one complete revolution about its axis is 243 Earth days. This is longer than the Venus year, of 225 Earth days. Also, since the planet rotates in the opposite sense from its direction around the Sun, its day—the time from noon to noon for a point of the planet—is 117 Earth days.
Would-be world-builders please note: It is difficult to visualize the relation between the time a planet takes to rotate on its axis (the sidereal period), the length of its day (from noon to noon), and the length of its year. However, there is a simple formula that relates the three quantities. If R is the time in Earth days for the planet to rotate on its axis, D is the length of its day, and Y the length of its year, then 1/D=1/R61/Y, where the plus sign is used when the planet rotates on its axis in the opposite sense from its travel around the Sun. For Venus, Y=225 Earth days, R=243 Earth days, so D=1/(1/243+1/225)=117.
* The pale yellow clouds of Venus are not water vapor. They are sulfuric acid, the result of combining sulfur dioxides and water. These sulfuric acid clouds stop about 45 kilometers above the surface, and below that everything is very clear, with almost no dust. The whole atmosphere is about 95%
carbon dioxide. The lighting level at the surface is roughly like that of a cloudy day on Earth, though there are frequent storms in the clouds, and lots of lightning.
* The pressure at the surface is about 90 Earth atmospheres. Such a pressure may seem to offer impossible problems for the existence of life, but that's not the case. A sperm whale, diving in Earth's oceans to deeper than a kilometer, comfortably endures a pressure of more than a hundred atmospheres—and returns to the surface unharmed a few minutes later. We still don't know how the whale is able to do that.
* Venus is hot. In this way the modern picture of Venus is like the old one, but it is probably hotter than anyone expected. The surface temperature is somewhere between 460 and 480 degrees Celsius, and highly uniform over the whole surface. Since the axial tilt of Venus is only about 6 degrees, there are no seasons to speak of.
Venus is hot for the same reason that a greenhouse is hot. Solar radiation gets into the atmosphere easily enough, but longer wavelength (heat) radiation from the surface is then trapped by the thick carbon dioxide atmosphere (or glass, in the case of the greenhouse) and cannot escape.
* Thanks largely to the Magellan spacecraft, we have a high-quality radar map of almost the whole surface of the planet. (Note: We still lack such a complete radar map of the surface of the Earth.) Venus is a barren place of rocky uplifts and shallow, melted-down craters. It is nothing like the old stories; no swamps, no intelligent amphibious life forms, no artifacts but a few burned-out spacecraft from the Soviet Union and the United States. But there are mountain ranges, well-mapped by orbiting imaging radars, and a great rift valley, bigger than any other in the solar system.
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