| Cryonics, December 1988
[Copyright 1988 by Davis Publications, Inc. Originally published in Analog Science Fiction/Science Fact (September, 1988). Reproduced by permission of Davis Publications and the author.]
"You were only 10 years old, full of running and jumping, ballgames and 'Masters of the Universe,' when they told you that you had osteogenic sarcoma. You cried and begged your mother not to let them cut off your leg. Five interns had to hold you down when you tried to run away. When you woke up, your right leg was cut away at the knee."
We don't like to think about our own vulnerability. Every day, accidents and disease severely injure people just like us. They happen quite unexpectedly. One day everything seems to be going well and the next day, we face utter terror. And this is not a terror of an invasion of green spiders from Arcturus, but an ordinary terror, happening to our next door neighbor or to ourselves.
This article is about medicine in the 24th Century. But we need to stand back from the subject first, for perspective.
In the 17th Century, more than 50% of all children born never lived past age ten. Nineteenth Century writers like Dickens wrote death scenes -- children dying of cholera, or whooping cough, or diphtheria, or scarlet fever. . . . People died at all ages. Smallpox scarred others for life. Nobody liked this fact, but it was so common that everybody lived their lives without ever thinking about it, unless it suddenly became real, for themselves, their wife, or their children. And if so, nobody else paid attention. The invisible terror remained invisible to them, and so thankfully, they went about their own affairs.
These diseases were an unseen background to life. Wealthy families would leave town every year in the cholera season. City fathers would shut up houses on quarantine. People would not often talk about their vulnerability any more than they now talk about the color of the sky.
But the other side of vulnerability is heroism. If no injury were final and we could put everything back as good as new, heroes become impossible. Invulnerable people can't even fall in love. Nobody writes stories about them. They have no problems. Today we are invulnerable to diseases which once brought terror to whole cities.
To understand medicine of the 24th Century, we have to understand the thin line between vulnerability and invulnerability. This line dominates our lives night and day. It is so important that we learn to walk along it without even thinking about it, any more than we think about breathing. And yet, whether we experience happiness or despair depends on where that line falls for us.
The most important point about 24th Century medicine is this: that line will fall elsewhere.
For science fiction writers, vulnerability and invulnerability are also essential. If unshielded high-dose radiation is no longer dangerous, that's bound to affect the story. If bad guys once "killed" can come back, or people can recover from gaping ax wounds to the head, the entire meaning of a fight is transformed. Amazingly, events in many science fiction stories depend on injuries or diseases likely to be trivial problems a few centuries from now. Who today would write a story about a little girl's death from scarlet fever? Nobody dies of scarlet fever any more.
Of course we might totally redesign ourseles. But some human traits are so fundamental to almost everyone's conept of who they are that they will actively resist any redesign, for themseles or for their children. In some fundamental ways people will not change. In other ways they may change profoundly; but the points on which they stay the same are just as important. In Box 1, I list some essential human traits, and others where redesign might happen.
BOX 1: CONSTANCY AND CHANGE
Biological control implies the ability to change human design. Here are some things about ourselves we will want to keep, and others we will change.
We can imagine ways to turn people into docile slaves, to rework them as parts of spaceships, or turn them into six-legged creatures living on the floor of ammonia seas. But this article isn't about what can be done to one group of people by another. That is assault rather than medicine.
We do not want anything done to us which will make us something else entirely, or that will make us say: "that is not me." But who are you? Here is a test for biological changes to human beings: If people can be found who genuinely want such a change for themselves, then it will happen, and in some sense is a subject for medicine. All other events constitute assaults. Assaults will happen: but they are the problems of medicine rather than its success.
What is most important about identity is that our bodies and our senses are not external tools. We are our bodies. We cannot take them off or put then on like clothing. Our nervous system maps our own particular body. We can't just hang new eyes on like binoculars. If we had the eyes of eagles, we'd need the brains of eagles to use them and the feelings of eagles to respond to what we see. These feelings, the neurology underlying our senses and our body, are far more important to our sense of self than just a piece of anatomical equipment.
Medicine is a branch of technology, but not just a branch of technology. We demand of our doctors that we trust them. They reach into parts of ourselves very important to us. Anyone who changes our body is also changing our soul. Some of the transformations I discuss in this article may not seem related to medicine at all. But all of them involve changes which are terribly important to us. We will not allow these things to happen casually, or be done to us by a random stranger. One way medicine differs from other fields is that it invades the soul.
And so we see one kind of 24th Century terror: that you are one day kidnaped and integrated into a spaceship. And from this assault you will need healing, to return you to a human state. Tomorrow's physicians may have to force you not to be a spaceship. In such a situation not just your body is injured, but also your soul. We will have to discuss how healing of our souls, of the very essence of what we are, could come about.
We can best judge the capabilities of 24th Century medicine by looking at what living things can do now. If today's animals or plants can do something, then some way exists to do it under complete human control. We will make quasiliving creatures, not just of the size and complexity of viruses, but up to and including the size and complexity of redwood trees or whales.
Learning to manipulate living creatures is exactly like learning to use alien machines whose vanished owners built them for unknown purposes and with locks to prevent unauthorized use. Living creatures are independent of our wishes. Their entire design aims toward their own perpetuation and defense. We can't transplant organs from animals because of their (and our) immune systems. We can't mold them like clay because they try to retain their own forms. The creatures we will build will have no such independence. They needn't even have drives to find their own food.
To some unknown degree, we will also make creatures with biochemistries quite unlike any which have yet developed in nature, or that ever could develop in nature. For all current Earth life, water is the major solvent and transport chemical. But ammonia supports biochemical reactions. Silicone fluids which freeze at -100°C, forms of oil with higher boiling points than that of water: all these might support enzyme chemistries broadly similar to our own. Oceans of silicone fluid just won't happen naturally, but they need not happen naturally for us to make biochemistries based on them.
The simplest forms of such machines would be single cells, like macrophages. Macrophages are part of our normal defense mechanism. These cells move about inside our tissues, destroying old and foreign cells and other debris. They slip between existing cells, accessing every part of our body. Cell membranes aren't solid walls. Artificial macrophages could pass through and between cells, reaching any body tissues. They could deliver genes or chemicals, take control of their target cells' metabolism, or even replace target cells entirely by budding off a new copy. Normal macrophages use the bloodstream for transport. Artificial macrophages could use the bloodstream too.
BOX 2: WHERE ARE WE NOW: MACROPHAGES.
By now (1989) virologists routinely create modified viruses to place specified genes into DNA of target cells.
Attempts to cure one disease, Lesch-Nyhan disease, are imminent. Lesch-Nyhan disease, which causes mental deficiency and uncontrollable self-mutilation, results from a single missing gene. Because Lesch-Nyhan disease is so simple, primitive genetic surgery will work. Full genetic surgery needs much more capability. Sometimes host cells turn off inserted genes. Again, transfer viruses can put genes into the wrong cells, where they cause new kinds of pathology.
The problem is that most genes require regulation by others. A. D. Miller and others at the Salk Institute have created a virus carrying not just a gene, but its regulator genes, into host cells (A. D. Miller et al, Science, 225, 933-938 (1984)).
To keep transfer viruses from reproducing, we create modified viruses lacking genes for chemicals essential to reproduction. We grow up many transfer viruses with a second virus (called the helper virus). The helper makes the essential chemicals. After separation from helpers, these viruses can insert their cargo of genes into cells, but not grow in them.
The macrophages I discuss are much more elaborate. They can carry much more control machinery to recognize target cells, responding only to them, or responding differently depending on cell type or cell conditions. They can still work even if the target cell isn't functioning (viruses can't do this). They can rebuild target cell machinery other than the genes. They can also transfer many more genes, up to an entire copy of the patient's genome.
R. D. Cone and R. C. Mulligan, "High efficiency gene transfer into mammalian cells: generation of helper-free recombinant retrovirus with broad mammalian host range," Proc Natl Acad Sci, 81(20), 6349-53 (1984).
M. A. Eglitis, P. Kantoff, E. Gilboa, and W. F. Anderson, "Gene expression in mice after high efficiency retroviral mediated gene transfer," Science, 230, 1395-8 (1985).
A. D. Miller, M. G. Rosenfeld, et al, "Infectious and selectable retrovirus containing an inducible rat growth hormone minigene," Science, 225 933-8 (1984).
Artificial macrophages will be able to communicate with one another. They could release diffusible chemicals to guide one another's behavior. Based on what one set found in the retina, for instance, others could carry out special modifications in the visual cortex. These devices could form an integrated repair system much larger than a single macrophage.
Some repairs will need delivery of materials to a repair site much faster than the circulatory system provides. We'll need devices to grow their own support tissues into a patient. For instance, severe crushing or mangling injuries will require us to provide a new vascular system. The repair device might resemble a fungus, growing mycelia into the injured tissue. The mycelia would grow between existing cells rather than destroying any. We can call such devices repair nets. A repair net will work together with a whole family of macrophages. For instance, the macrophages could reach their target through the mycelia of the net.
Many of our organs have few provisions for self-repair. That means that repairs must be done externally. If our heart is injured, we lack a backup heart. Furthermore, some modifications and transformations require external support simply because our bodies have no way to bring enough materials and energy to the repair site. The final level of repair machine would actually take over metabolism of a patient from outside.
We can therefore expect devices which would enfold a patient completely and carry out repair. We have a model for such devices already; the womb. It supports the infant by externally supplying blood and oxygen and removing wastes. But such a device would have even greater power to control growth and development of the patient inside it. It would take over from the patient's own genes, controlling growth according to the patient's own genetic program. Such a repair device would have a brain, to manage its control and maintain homeostasis. It could take apart a patient's entire body cell by cell, rework it into something new, and return the cells to their original location. I will call such a device a chrysalis.
Chrysalises, repair nets, and macrophages are types of machines. They would have many specialized forms for different jobs. They would have programmability. Some would be adapted to replacing only particular organs. Some repair nets could force rapid wound repair. A broken bone, for instance, would be set inside a repair net bandage. This would grow into the tissue, controlling and promoting repair. Others would be adapted to reworking and repairing nervous tissue. Some chrysalises would specialize in reviving "dead" tissue, such as severed limbs. These would be reattached after revival by another chrysalis.
The ability to design whole animals and plants to specification also means complete contol over existing creatures, their metabolism, growth, and development. Since cancer is a disease of growth and development, we can expect that cancer would be a long-vanished probem. But control over growth and development mean not just an end to caner, but also the ability to faciliate rapid and comlete wound healing, regeneration of lost limbs and organs, and the reversal of aging.
Growth and development are now almost completely beyond our control. Today, whenever we want to alter the shape of bone or tissue we use surgery. But all of today's surgery is only a crude makeshift. A medicine based on control of growth and development would treat problems very differently. It would allow us to alter the shape of bone or tissue by a kind of directed growth. Millions of macrophages would enter the patient, controlling growth or breakdown of our tissues. Similar methods could modify individual cells. A genetic modifier would be a macrophage-like cell. Millions of these would enter a patient, search out target cells and individually change, remove, or modify their genes.
BOX 3: WHERE ARE WE NOW: DEVELOPMENT
As far back as the 1930s, scientists developed indirect evidence for morphogens. These diffused through the body of a growing animal, and their concentration at particular locations told cells there what to do. One known morphogen is a derivative of Vitamin A, all-trans-retinoic acid. It controls the growth of chicken limbs. Morphogens for slime molds and hydra are known (C. Thaller and G. Eichele, Nature, 327, 625-628 (1987).
One class of DNA control sequences, the homeo box, characterizes genes controlling development in fruit flies, flour beetles, mice, and man. Specific homeo box genes are active only in specific segments of mice and fruit flies. Mark Krasnow and others at Stanford have traced interactions between homeo box genes (one gene turns on or off another) in fruit flies (M. Robertson, Nature, 327 556-557 (1987)).
Morphogens allow very fine guidance of repair and removal of misplaced tissues by artificial macrophages or nets. These devices could also recognize cell types and even to which segment a cell belonged. They could turn on growth and division genes in cells where these are normally off, and guide the resulting growth.
Sheard, P., and M. Johnson, Science, 236, 851 (1987).
Utset, M. F., Awgulewitch, et al, Science, 235 1379-1382 (1987).
What medical problems do we have now that we'll still have in the 24th Century? The major problem will have to be physical injury: broken bones, damage to internal organs or the brain, people sliced open by machinery, knifings, gunshot wounds. Machinery will still malfunction. People will be hurt, often far from places where full-scale medical help is available.
Ideally a First Aid kit is something everyone can carry with them in their wallet. What problems could a First Aid kit deal with? How would it work?
The First Aid kit might consist of machines bound together into a package the size of an aspirin tablet. These machines would get some or all of their materials and energy from the patient's own tissues. People going into dangerous situations might build up their resistance by vaccines of the kind I'll describe in the next section.
Medicine based on control over growth and development will make almost no use of surgery. Many problems requiring surgery now, like cancer or heart disease, simply will not occur. Yet surgery is the most important function of hospitals today. Even without surgery, though, less portable or less common equipment will belong in hospitals. Patients will have devices growing into them or enveloping them, sometimes much bigger than they are. Here is some equipment which will probably be available.
Hospitals involve much more than this. Right now, we take someone to the hospital for serious conditions. Someday our serious medical problems will be trivial. Serious problems for 24th Century medicine would be utterly impossible for us today.
Medicine doesn't just consist of cures for known diseases which everyone believes are someday curable. It consists of cures and treatments for conditions which are now so far beyond treatment that they don't even have a name or seem to be disases. Now, in 1989, we call all such conditions by only one name: "death." But "death" conceals a multitude of "diseases," each one of which must have its own individual cure. It falls apart into a million different conditions, some of which they will know how to treat, others not, and others which will be subjects of intensive research. For 24th Century medicine will not be the same as 26th Century medicine. . . .
Since our brains contain our selves, chrysalises might work only on the brain, simply regrowing the rest of the body.
However, chrysalises won't be able to restore lost information. But information which would allow reconstruction of the patient's identity very likely survives for much longer periods of time than are now compatible with restoration of life. Intensive research goes on now on how to revive brains deprived of blood flow for up to an hour at normal body temperature, with tantalizing preliminary successes. Beyond about an hour without oxygen and nutrients, the status of brain cells becomes a great mystery. We know that extensive structure remains on a light-microscopic scale. On electron-microscope scales, some cell structures are somewhat damaged. We don't know how much structure is critical or how memories are stored and how durable they will be. Our permanent memories may be coded by changes in activation/deactivation of genes in each neuron. This would mean that personality would survive many hours after cessation of circulation. Anthropologists have recovered fragments of brain DNA from Indians buried 3000 years ago in the mud of a pond. So long as fragments of nervous tissue exist, chrysalises could reconstruct a brain from those fragments and a body around the brain.
Many current conditions of injury, including cryonic suspension, are very simple compared to problems for which chrysalises are needed. They probably won't need more than macrophages and nets for repair.
BOX 4: WHERE ARE WE NOW: DEATH REVERSAL
Since each form of "death" is a different pathology, I can't begin to discuss all the forms even briefly. I will discuss two questions:
During an initial period after formation, chemical and other treatments can erase memories. Afterwards, however, no known treatment disrupts memories without total destruction of neurons. Permanent memories persist for years. These facts suggest (but don't prove) great durability.
Currently, the leading theory proposes that chemical changes in neurons from learning resemble those of cell differentiation. Specific genes are turned on or off when a neuron acquires a memory (cf. P. Goelet, E. R. Kandel et al, Nature, 322, 419-422 (1986)). This theory would predict that memories, like differentiation, are very durable.
Two alternatives for memory are now disproven:
Our brains don't need continued electrical activity to remember. Audrey Smith cooled hamsters down to near 0°C, stopping all electrical activity. Afterwards, they remembered mazes they had learned.
The wiring diagram of neurons to one another also doesn't code memories. Since salamanders can repair massive brain injury, Paul Pietsch cut salamander brains into pieces, scrambled the pieces, and reimplanted them. These animals recovered, and also remembered. Furthermore, mollusks such as Aplysia can achieve very rudimentary learning. Their nervous systems are small enough that we have mapped them completely. Their connections don't change with learning.
Allport, S., Explorers Of The Black Box, W. W. Norton, New York, 1986.
Goelet, P, E. R. Kandel, et al, Nature, 322, 419-422 (1986).
Pietsch, P, Shufflebrain, Houghton-Mifflin, Boston, 1981.
Martinez, J. L. and R. P. Kesner, Learning And Memory, Academic Press, 1986.
Smith, A. U., Biological Effects Of Freezing And Supercooling, Williams and Wilkins, Baltimore, 1961.
Commonly, if you aren't drugged or cooled down, after 5 to 8 minutes without blood flow, current medicine can't revive you. But this isn't the whole story. Over the last 20 years, a quiet revolution has taken place. Reviving brains injured by prolonged lack of blood flow has become a major research problem.
In 1969, K. A. Hossmann and S. Sato revived electrical activity in cats' brains left without blood for an hour. Several drugs improve recovery, including naloxone, verapamil, nicardipine, gangliosides, taurine, and others.
Unfortunately, since Hossmann and Sato, clinical treatments for brain damage haven't yet materialized. The problem turns out more complex than neurologists hoped. Even partial success, however, means a great advance in treating strokes and brain injury.
Neurons don't disappear instantly when deprived of blood flow. They gradually decline over four days. Protein synthesis fails in these injured neurons, and they become hyperexcitable. These two events eventually kill them.
Since brain damage matures over days rather than instantly, macrophages can take control of injured neurons, provide any protein synthesis ability they lack, and guide them back to health. Treated brains would look inflamed. Other macrophages may weaken skull bones to allow swelling.
Most citations here are for recent work on the subject:
Baskin, D., et al Nature, 312, 551 (1984).
Drejer, J., et al, J Neurochem, 45, 145-151 (1985).
Karpiak, S., et al, Stroke, 18, 184-187 (1987).
Hossmann, K. A. and S. Sato, Science, 168, 375 (1987).
Suzuki, R., et al, Acta Neuropath, 60, 217 (1985).
Thilmann, R., and M. Kiessling, Acta Neuropathologica, 71 88-93 (1986).
"Death" isn't the only "impossible" problem that will be treatable by 24th century medicine. Brain and spinal cord injuries currently devastate their victims. Active research goes on to repair these problems too. For both rats and monkeys, normal adult neurons in their brains will divide. Control of growth and development specifically includes restarting growth in cells which have normally ceased to grow. Macrophages can enter these cells and rework the genetic controls on growth.
Ability to recover people after such serious injuries necessarily means the creation of whole classes of identity-damaged people. These will be people who have lost whole sections out of their previous lives because of some brain injury, now totally repaired. You may have been married to a woman for 40 years, but after injury and repair remember nothing of her. The way we act toward stroke patients tells us that we're certain to treat these people not as new people but as the same people they were before injury. But it will be a new kind of brain injury, one we don't have today because all such patients now die. And it will be a kind of brain injury no amount of biological control or repair can cure.
The most important biological changes we make to ourselves will be invisible, such as changes in metabolism and repair, and changes in mental processing. We would use our ability to control life to allow us to metamorphse into new creatures able to live in new environments. Macrophages could remodel our cells to have these traits, a kind of vaccination for new environments.
Not everyone would metamorphose. Protective clothing is often the best adaptation of all. But even simple adaptations to cold or vacuum become important for workers in prolonged contact with hazardous environments.
Metamorphosis may require such a thorough rebuilding that our metabolism cannot run normally while it goes on. With a chrysalis providing external support, quite profound rearrangements of metabolism become possible. Here's how to redesign someone to live in a cryogenic ecology on Titan (the ecology itself may be man-created. We may create animals and plants able to live on many planets where life could not evolve naturally).
We must rearrange someone's entire biochemistry in every single cell. First, freeze them down to the low temperature to which they are to be adapted. Second, the chrysalis grows in between their cells, much as in cellular repair. Of course it has the proper metabolism to operate at
-200°C.The chrysalis then individually rebuilds every cell into cells with cryogenic metabolism. It sequesters the patient's memories and maps them cell by cell onto similar structures in the target organism. The chrysalis then withdraws in reverse order. The metamorphosis is done. The man may awaken as a cryogenic creature.
Of course, metamorphosis needn't rebuild someone's whole body in all cases. For instance, our liver performs critical functions in storing energy (in glycogen) and detoxifying foreign chemicals. We may wish to rework our liver so that it will also store oxygen, as part of adapting someone to live unprotected in space. A net could substitute while rebuilding the liver from outside.
Of all the suggested modifications to human beings, only one has extremely vocal, serious, and organized proponents right now. That is biological immortality. Its most organized proponents are the cryonics societies.
Clearly means can exist to prevent and reverse aging. And they do raise an issue about identity. Most people think of themselves with finite lifespans. They say: "That will happen after my time," or "I'm glad I won't be alive to see that." They have planned out their whole lives on the basis of their mortality. They go to school at a certain age, marry, have children, plan on leaving an estate on their death. Faced with the possibility of indefinitely long lifespans, they ask if they would continue to be themselves if they were immortal. There is no easy answer to that question.
We can deal with the deterioration of aging, including brain and heart malfunctions, by permanent alterations in our ability for self-repair. Modified people could survive indefinitely in good health without growing old. Body structures like teeth, which slowly wear away, could renew themselves by slow growth of new tooth material (as rats and rabbits do). If you live long enough, however, you are certain to suffer a severe accident. That accident will need external repair.
Old age has no positive evolutionary effects. Fundamentally it happens because our "natural" life styles rarely allowed people to live to age 70. Now, with so many people surviving to 70 and beyond, we literally run out of biological programming. The symptoms of this loss of programming are what we call old age.
Preventing and reversing old age will happen because people who did not age would have an evolutionary superiority to those who did. They would not spend so much energy supporting infants and young children. Nor would they burden their own children with their care in old age. Right now, about 50% of the population is dependent on others as a result of age (too much or too little). Everyone takes this biological burden for granted, just as they once took it for granted that most children would die before age ten.
BOX 5: WHERE ARE WE NOW: IMMORTALITY
Intervention. Immortality (absence of aging) is a subproblem of development. Gerontologists have known that low calorie diets with all essential nutrients double lifespans since work by Clive McCay in 1934. These diets cause unknown changes in hypothalamic hormones. Serotonin is somehow involved.
The major reason why aging research has not advanced further with this problem is the emotional turmoil felt by funding agencies and scientists themselves at the concept of interfering with aging.
McCay, C. M., et al, J Nutrition, 18, 1 (1939).
Timiras, P. S. and P. Segall, Federation Proceedings, 34, 83 (1975).
Most evolutionary biologists would explain aging as a secondary effect. Animals in nature die of starvation, disease, or predation before they grow old enough to show old age. Their lifespan corresponds to just past the point at which, in nature, almost all are dead anyway. Their bodies have self-repair programs telling what to do up to that age. Our own life conditions are much better than formerly. We almost all live long enough to run out of programming. Old age is the symptom of this running out of programming.
References and Notes
G. C. Williams, "Pleiotropy, natural selection, and the evolution of senescence," Evolution, 11, 398-411 (1957)
About 1984 or earlier, K. Eric Drexler circulated ideas for cell repair machines, based on a mechanical tradition. These contain important new ideas, particularly calculations on sizes and implementation. Unfortunately his book, Engines Of Creation (Anchor/Doubleday, New York, 1986), lacks a technical appendix describing these.
Conditions of life can change so much that traits once useful become actively harmful. It's not easy to predict future conditions of life and their problems. To 17th Century doctors extra weight was a cushion against disease and a reserve for hard times. The concept that obesity could cause problems would seem absurd. Problems associated with obesity only appear at ages few 17th Century people would have survived to. More to the point, obesity was then a positive trait, a sign of health, wealth and beauty. A 17th Century doctor, having seen the long term disadvantages of obesity, would then have to decide to do away with this form of beauty.
We may be seeing one "disease" like this now. Getting good jobs in 1989 requires some level of technical skill. This learning takes personal traits (emotional ability to study and listen) and brain processing. Someone without these traits finds academic learning hard: this is now classified as a disease and called a learning disorder.
Mental and emotional skills someone would need to do well in 24th Century society won't just be enhancements of current abilities. To do well, we'll have to lose some abilities we now have. Someone from the 24th Century may well appear less intelligent on all our current tests. For instance, current tests require subjects to follow orders. With much or all of production and distribution automated and the disappearance of "workers," following orders could become a far less valuable and even contrasurvival trait.
The metamorphosis needed, a slightly rearranged brain, will be simple to carry out in practice. But our whole personality is bound up in our abilities or lack thereof. To change these abilities involves many questions medical technology won't answer. A sufficiently advanced technician might appear indistinguishable from an idiot. Do you want to become an idiot?
All currently known medical problems will be easy exercises even for novice doctors of tomorrow. So what could go wrong? Let's look a little at history.
In the Middle Ages, wolves ranged freely over Europe. They disappeared from England first of all, but even in 1500, wolves remained abundant in France. In the wintertime, they came in packs into Paris and ate children, dogs, even adults whom they found alone on the streets. Today we no longer have problems with wolves eating our children.
Wolves are wild things. So are viruses and bacteria. In 2388, people will no more suffer from predation by wild bacteria than they now suffer from predation by wolves. A second class of current diseases are the diseases of development, like heart disease or cancer, in which normal growth and development become deranged. Fundamentally, they stem from aging, which is the most fundamental process of growth and development. Of course, as a result of our control over genetics, growth, and development, all such diseases will disappear, together with aging itself.
If human beings take complete control of life, human beings will be the cause all medical problems. That is, problems will consist entirely of accidents and assaults.
Crime is another form of predation. Chrysalises, nets, and macrophages could all be turned to criminal use. Specially constructed macrophages could enter our brains, change our memories and desires, and turn us into the slaves of their creator.
Accidents needn't just consist of broken bones. People can be injured by release of biological agents or toxins. Many 19th-Century doctors spent years working out causes for diseases. Even in this century, doctors had to unravel the causes of Legionnaire's disease and AIDS. Similar detective work will go on in the 24th century. It will involve not just seeking out harmful chemicals. We would have to search out harmful nanomachines, creatures able to multiply and grow. But unlike the 19th Century or the present, such creatures would be entirely man-created.
History suggests another change too. European populations so easily overwhelmed the peoples of the Americas because Europeans arrived carrying many deadly diseases. Centuries of plagues gave them immunity. The Indians had no such immunity. As many as 90% of them for five generations after the Europeans came died of terrible plagues such as measles and smallpox.
If the major disease problems of the 24th Century will consist of accidental or deliberate release of organisms, then we can expect that the people of that time will carry with them appropriate enhancements of their immune systems. These enhancements, just like the diseases which made them necessary, will be man-created. Anyone of the 24th Century will be able to resist bacteria/devices which would instantly kill any unprotected person of our time. If hostile nets can invade our brains to take control, then we'll have equally clever defenses against them.
Control of living things puts responsibility for life or death on us, not on the wolves. Any analysis of human nature tells us that we could become very sick in the 24th Century.
Nevertheless, we now live at the leading edge of a very long historical trend toward longer lifespans and less sickness, and even less death from other causes such as accident and murder. This trend tells us that people of the 24th Century will live much longer lives and expect even longer ones; lifespans stretching across millennia. But that is a statement not about medical technology, but about our own use of it.