The exterminator just left. It wasn't his first visit here. One month ago our apartment building was invaded by cockroaches and we are still fighting them. It looks like we are losing this war - within three days the insects are back. Humiliated by the defeat I started working on a new battle strategy. If we cannot defeat them in a straight, honest fight, maybe there is another way of overpowering these disgusting little monsters.
I noticed with terror that I was slowly getting used to them. I'm far from adopting one for a pet, but the sight of a dark crawler on the floor doesn't cause the wave of repulsion anymore. If we can't get rid of them and can get used to them, why not make them work for us? In the era when biotechnology is in a phase of explosive growth, it shouldn't be too difficult to construct new strains of roaches that will be useful for us. Properly reprogrammed insects can replace environmentally unsafe and expensive vacuum cleaners. A few changes in their genome, a little bit of training, and the roach becomes a necessary commodity in every home. Imagine: as soon as the darkness sets, hordes of little cleaners leave their nest and systematically scan your house, collecting the litter, both edible and inedible. Your job is to clean their nest every few days and feed them. Sounds easy, but, of course, it would require some hard work to achieve that. We would have to control their reproductive potential so they multiply only when needed, to adjust their dietary preferences so they eat only specially pre-treated food and not table scraps and modify their nesting habits, so they live more like ants. And that would be only the beginning, the dawn of a new era. There are billions of other pests, roaming the world like natural "wild robots" with a multitude of useful capabilities, just waiting for us to reprogram them and use them for our own purpose. There is a huge, profitable market waiting out there!
It seems that something similar has been happening in Nature for a long time - parasites gradually becoming useful and then indispensable to organisms that they invade. The proof? The natural history of many great epidemics follows a pattern. First, the disease suddenly appears "from nowhere" and voraciously attacks humans. Hardly anyone is resistant and huge numbers of people die. One doesn't have to reach far for examples: medieval epidemics of Plague or Small Pox in Europe, European diseases that decimated native Indian populations in the Americas, or the modern plague of AIDS threatening our world.
The next phase can last from years to centuries. A disease becomes less virulent and spreads silently in the population, not killing anyone or killing a few slowly. A good example is syphilis, probably imported to Europe from Americas during early years of the Conquest, spread rapidly in promiscuous Europe. The disease then was quite unlike the syphilis that we know today. It was very similar to the most severe forms of leprosy, stripping its victims' flesh to the bones. Apparently that prompted society to try to isolate victims of the disease. There were special ghettos for people with leprosy, a perfect place to isolate syphilitics. There was only one unforeseen obstacle: inhabitants of the ghettos were so afraid of the new, deadly disease that they were ready to fight and barricade themselves in the ghettos to avoid the risk of getting infected. Today syphilis is a relatively "benign" malady: after the occurrence of primary and secondary lesions patients may live for decades, not even aware that they carry the disease.
Some of these illnesses disappear altogether with time and we are left only with the exotic description, like "sweating sickness" (Sudor Anglicus) of seventeenth century. On the other hand there are illnesses that have been with us for thousands of years and don't show any signs of easing up as in tuberculosis. Its signs were found in some of the oldest Egyptian mummies. Thousands of years later, the disease is still here, as deadly as before. The explanation is the nature of the infectious agent itself, its ability to mutate, thus giving birth to the new strains of bacteria which cause clinically indistinguishable disease. Eventually, killer viruses and bacteria "became domesticated" and live in our bodies to mutual benefit. Some of them, like E. coli, live in the human bowel, supplying us with vitamins and defending us from invasion of other, virulent organisms. At that stage the relationship is rather loose, new or foreign strains of E. coli can cause disease, well known to anyone who traveled around the world, as "travellers' diarrhoea".
In the next step there is a nearly total loss of identity, unification of both organisms, bacteria or virus becomes a permanent and irreplaceable part of the cell, to the degree that the cell is unable to survive without this new, incorporated organellum. All higher organisms require mitochondria for their oxygen metabolism, and mitochondria are assimilated bacteria, unable to live on their own outside cells, but still preserving their own genetic information and multiplying independently from the host cell. Without mitochondria there would be no life on Earth as we know it. These organella enabled cells to survive toxic levels of oxygen that accumulated in the environment due to the photosynthesis. As a consequence "new" cells were able to jump to the next level of evolution and to thrive in previously poisonous environment.
The final stages involve ultimate "melting together" of two organisms: former invader and invaded. Certain viruses are known to "hide" their nucleic acid in the host genome. If this union works, the result is a new quality, new genetic sequences that can be passed to progeny. It is by no means a smooth process! Sometimes this marriage is not compatible and the viral genome is released again, causing disease after years of silence. Occasionally the fatal piece of genetic information is shuffled around the host genome, in the search of the compatible spot. That process can de-stabilize the cell causing unpredictable, wild growth (we call it a cancer) or death of involved cells. This cycle can occur during the life span of an individual (like in a case of Human Papilloma Virus infections that may lead to the cervical cancer) or last beyond it, causing malignancies in the following generations.
Does it mean that infections, while they can be lethal to the affected individual, may actually be beneficial for the human species as a whole? If evolution happens indeed only on the molecular, bacterial and viral levels, it might be that humans and other "higher" organisms are the parasites that benefit most from infections, "stealing" valuable genetic material from viruses and bacteria. Our chromosomes may be too bulky and too slow to react fast enough to the changing environment. Since viruses and bacteria can multiply faster and adjust more readily to changes in the environment, they are a "cheap" and abundant source of valuable, "field tested" genetic material needed for our evolutionary progress. New, successful genes, formed in bacterial or viral genome can spread rapidly in the animal and plant world, incorporated by all organisms that can get hold of them. Unfortunately nothing in this world comes for free. The price we pay as individuals for survival and evolution of our species is high: the death toll of victims of epidemics, common infections and cancer. Is this price too high? Well ... maybe, but do we really have a choice?