As mentioned earlier, the development of effective ways to combat viruses will represent a major medical turning point. If viral diseases can be conquered without hospitalization, the cost of medical care will decline and life spans will increase--both perhaps rather substantially. Enough progress has now been made to make some health researchers confident that most infectious diseases will soon be a thing of the past, providing no intervening political or economic catastrophe sets the work back.

This leaves three other categories of organic malfunctions for which to consider treatment strategies. The first is invasive illness, such as cancer. Here, encouraging progress has already been made toward the development of biological and chemical agents capable of targeting specific cancerous cells in the body and either destroying them or tagging them in such a way as to invite the body's own immune system to eliminate the intruder. It is now known that a healthy immune system is able to make antibodies for almost any foreign protein; the trick is to keep that system healthy and working. Whatever the method, many forms of cancer can now be completely defeated, especially if detected early. The most difficult remaining ones to overcome may be the non-localized cancers of the bone, blood, and lymph. Still, optimists point to the progress to date and predict that even these forms of cancer will be curable by injection, radiation, and other nonsurgical methods within twenty years.

Lung cancer may also be hard to cure. It is presently on the rise, especially among women, who became smokers in large numbers more recently than men and have not been giving up the habit as readily. This particular problem raises a subsidiary ethical question--whether the production, sale, and advertising of so potent a carcinogen as tobacco should even be allowed. It would not be if it were a new food additive or drug, but the vested interests of a large existing industry are not easy to set aside, even when the lives of many people are at stake. This is an example of the way that economic considerations sometimes overpower ethical ones.

The second category of malfunctions is those involving the accumulation of extraneous material in the body. Calcium deposits cause painful spurs on bones and cholesterol accretions block arteries, causing damage to the heart and other organs. It seems likely that in many cases, substances will eventually be developed to dissolve such accretions in a harmless fashion. After all, there are already drugs that can dissolve gallstones or block secretions of stomach acid. These eliminate the need for such surgeries as gall bladder removal and duodenal ulcer repair.

In an interesting sidelight, it was long thought that ulcers were caused by excess stomach acid, and the typical treatment was a sedative prescription combined with a bland diet. It is now known that ulcers are caused by bacteria, and antibiotics are quite an effective treatment. That is, rather than being a systemic failure of one's own body, ulcers are caused by an invasive agent. There may well be other such misunderstandings in modern medical knowledge.

Another problem that may be of a similar type (system failure) relates to body cells' seeming inability to divide and replace themselves more than a given number of times before dying. One theory was that this may be due to the action of substances that built up between or inside the cell and eventually blocked its reproduction. If the cell-division inhibiting agents could be identified, an anti-inhibitor could surely be designed. Understanding what to do is not the problem here, the difficulty lies in actually performing the necessary engineering. But even if an accretion-dissolving molecule must be designed atom by atom--and the ability to do that is limited as yet--such design problems are not theoretically insurmountable. In fact, overcoming barriers of this type involves only a modest expansion of today's already formidable battery of pharmaceuticals.

A new theory of cell aging is equally interesting. It suggests that multiple copies of sequences called telomeres at the end of DNA chains vanish one at a time with each cell division. Eventually, no telomeres remain, and the cell can no longer duplicate itself, thus limiting the organism's lifetime. Perhaps an agent can be found to change this action so cells can reproduce indefinitely. On the other hand, such a cell would bear a strong resemblance to a cancerous one.

The third set of challenges for medical engineering relates to repairing physical damage to the human body. In this context, one is tempted to view the body as a biochemical machine, albeit of extraordinarily intricate design. Unfortunately for the mechanics of this machine (the surgeons), their smallest tools are thousands of times larger than some of the very fine parts they wish to repair. Heavy structural members (bones) and outer protective sheeting (skin) are relatively easy to work on, as are the larger subsystems (organs). But as many paraplegics know to their sorrow, the nervous system is another matter. Sewing these with thread is like trying to tie up a flea with an ocean liner's hawser. Finding, let alone repairing, individual damaged cells is impossible with traditional surgeons' tools.

The engineering challenge here is to develop first the knowledge of the fine structure of the human body at the molecular level, and then the ability to design biological or chemical agents that can effect repairs at that level. This is not as far-fetched as it may seem, for the body can already conduct repair operations to a great extent, and some animals are even capable of regenerating severed limbs. Human bodies cannot effect this, because even as they grow in the womb, their cell tissue differentiates sufficiently to lose the ability to replace parts. However, the fact that such tissue could grow a limb at one stage of development suggests that it could be given that capability again when necessary. This is the point of working with stem cells (ones that retain the ability to produce various kinds of tissue), for these may be induced to grow a variety or organs or parts thereof.

If limb regeneration seems too grand a task, perhaps promoting the healing of severed nerves will be easier to do and reward far more people. Once again, the problem is one of biochemical engineering--of building the appropriate substances to stimulate the body to repair itself. An old engineer's motto is worth mentioning here:

There are more comprehensive repair problems, however. As the body's cells grow older they gradually lose the ability to replicate themselves correctly, or at all. As noted, this may be due to some inhibitor. It may simply be that the body's parts gradually wear out and so die or that each DNA replication causes some portion of the genetic material to be discarded, and eventually the cell simply lacks enough DNA to reproduce. That is, perhaps a body cell is not unlike a page of text that has undergone many successive photocopyings. After a time, the text loses definition, and it eventually becomes illegible. If the DNA of a body cell is subject to similar losses, its successors would eventually lose too much of its information content to remain viable. Here is yet another case where it is easy to visualize the problem and to have some idea how to fix it--on a large scale and a theoretical level. Engineering a solution that allows the body to repair or replace structures damaged by age is a much more difficult matter. It could involve the development of many biochemical agents, some natural to the body at some stages of development (enzymes) and others that are new drugs.

It should be emphasized in this respect, however, that the body subsystem once termed the "simple cell" is anything but. On the contrary, it is known to have a biochemical design of incredible complexity and sophistication--more so than any computer, for example. Thus, finding problems at the molecular level, and designing answers at the same level will not be a simple or a short task.

However, the potential for such medicine extends from simple cell repair to the dramatic and even to the far-fetched. If the human body could be induced to grow a new limb, then perhaps it could also be made to grow a new heart, lung, or liver and then to dissolve the old one. Restoring hair to the bald may not turn out to be difficult or even important. Restoring hearing to the deaf or sight to the blind is another matter, for both involve problems of fine structure whose repair is often not amenable to surgery but could be to new pharmaceuticals. Some have even wondered whether a "memory pill" could be devised to stimulate the brain in such a way that while under its influence anything heard or read would never be forgotten. Regardless of whether any of these are achieved, the principal research focus will be on replacing expensive and difficult surgical methods with cheap and easy chemical and biological ones.

One possible method of producing biological agents is to design cells, say, bacteria, to produce proteins that in turn could be used to make specific enzymes or antibiotics. Such living nanomachines could be developed much further--to the point where a collection of them can act as a miniature assembly line for new DNA, new proteins or new enzymes. Such substances could then be built to order, molecule by molecule. Other optimistically projected nanomachines would be programmable or instructable--and may be termed nano-computers or general purpose assemblers. The reconstruction of a damaged heart, liver, or other organ and even the rebuilding of damaged nerves or neurons could be well within the ability of agents made in this manner. Another possible technique involves the direct construction of DNA strands that can manufacture the desired molecules. Another still is the chemical stimulation of the affected parts to induce them to self-repair through growth. Although these ideas are still in their infancy, there are already machines that are capable of analysing or constructing specific protein molecules. In the longer term, nanomachines might also be employed to grow a PIEA as an implant in the brain or to make alterations to body or brain structures to improve both or to repair congenital or genetic damage in situ--not on a gross structural level, but by editing gene sequences.

Setting aside the more spectacular speculations for a moment, an important potential for the use of existing technology is in the computerizing information and activities relating to preventive medicine. In particular, the most important contributors to health--or to the lack of it--are nutrition and exercise. Although the appropriate levels of neither are known yet exactly, a great deal of general information is known about both. Average citizens have little access to much of this in ready form until they come under professional care for a back injury, obesity, diabetes, or a heart attack. Most people will not make use of what is known without such a powerful motivation, unless it is in a form that makes it very easy to obtain. This is an interesting but not insurmountable challenge to some in the high-tech industry, for if people had and used the available information on nutrition and exercise, there would probably be a significant decline in health care costs, and an increase in the average life span.

This is yet another instance where reducing the barriers to finding information has great potential. People who would not make a trip to a library to find nutritional data are more likely to do so if it is easily available in their homes via an appliance that they use frequently, and on which the presence of such information is advertised frequently. The Metalibrary would not itself solve health problems, but it might prove to be an important tool in providing people with the means to solve some of their own.

As understanding of the aging process, of preventative medicine, and of how to do molecular engineering grows, a substantial increase in life spans seems likely. Longevity researchers differ widely in their estimates of what the eventual human average life span could be, with figures of 200, 500, and 1000 years being tossed about. Even if one believes the more conservative of these optimists, and assumes that some of today's under-50-year-olds would live to, say, 150 years instead of to the current average of about 75 years, the social implications are staggering. At every stage in the development of longevity treatments there will be pressure from the rich, the powerful, and the intellectuals to obtain priority treatment. Moreover, since the already highly developed countries would have such agents first, the medical gap between rich and poor countries (and individuals) may grow even greater, increasing the destabilizing forces on world society. Some attempts might even be made to keep the fact of such treatments a secret at first. However, even if the recipients had complete facial make-overs and an entirely new identities, their continued survival could not long be kept from the rest of the wider population or from the citizens of other countries--all the more so since effective treatments for old age are likely to be independently discovered by many researchers more or less simultaneously.

Over the longer term, age sixty-five retirements, the whole concept of pensions, the hope of inheritances, and the ability of youth to obtain jobs vacated by their elders will all be affected by any substantial increase in life span. In addition, unless birth rates are substantially reduced, population sizes could increase dramatically. Some already crowded countries might restrict any longevity treatments that are developed to a small elite for this reason alone. Power and money concentrations could grow, not only because their holders might at first control the treatments but also because they would live longer and have more time to accumulate both.

Some of these problems might be resolved by pragmatic force of circumstances. The managers of large pension plans would either re-market their funds as general investment packages or go into a different line of work. The tax structure might have to change to limit accumulations of wealth. Perhaps a means would be found to encourage people to change careers every few years in order to alleviate the job entry problem. However, the social and economic disruption due to such changes would still be substantial. On the whole, these changes may increase inequities and tensions between the rich and the poor of the world--a prescription for disaster if the treatments are not seen to be fairly administered. Marriage could change, for it is even now seen by many as a temporary commitment during part of a longer life--such a view could become even more prevalent if life lengthens and bearing children were discouraged or forbidden.

There are also some balancing forces to contend with on this issue. While increased longevity would suggest much larger populations, the birth rate in industrialized countries has been declining for decades, and it seems likely to do so in third world countries as their economies change as well. The net result could simply be a stable but much older population, and an increase in the retirement age because of a lack of younger workers to take jobs.

It is also not clear whether people who live longer would also stay healthy for longer or whether they would merely have to spend more years in extended-care facilities for the aged. If the latter were all that could be achieved, the benefits would be small indeed. The most optimistic of longevity workers are convinced that the greatest benefits of longer life will come by extending the productive years of those people whose generation of new ideas and techniques most profoundly impact the direction of society. This is a large assumption, for many people are productive only in a few of their present years. One might also hope that more years will mean greater productivity, but this may be an occasional side-effect. It may equally be supposed that longer-lived people would gradually become less innovative and productive, and not contribute anything of benefit to others for most of their lives.

Thus, although human life may be extended considerably over the next few decades, the long-term implications of such increases for society as a whole are unclear. There may be a declining birth rate, a more stable and conservative population, upheavals in the job market, and the disappearance of some institutions catering to retirement as it is now known. Whether the extra years would mean "better" people from either a moral or educational point of view is unknown. History would seem to suggest that there would likely be the same proportion of scoundrels and saints regardless of how long both lived.

Another aspect of the increased use of medical drugs is the corresponding increase in their abuse. The more drugs that are discovered, the more mind-altering substances will be among them. Moreover, as the workings of the human brain and body become better understood, so will the ways of stimulating the pleasure centers. Consequently, one should expect that there will always be addicts. What is not known is whether the societal changes now in progress will result in a higher percentage of the population becoming "wired" for pleasure than at present, or whether a significant sacrifice of general civil liberties will have to be made to detect and eliminate such practices. This is already an important question, not just for athletes who attempt to perform better on drugs but also for the employees of railways, airlines, hospitals, and other places where human performance affects the safety of others.

Thus, it can be seen that the development of new pharmaceuticals, as that of any technique, is likely to have mixed results--some very beneficial, some much less so.