Viruses have none of the characteristics of living cells. Not only are they metabolically completely inert, but they also lack any of the structural characteristics we would associate with a cellular origin, such as a nucleus, mitochondria, ribosomes, membrane pumps and so forth. They have a coat, but there is almost nothing under it. There is no way that a virus could be considered alive, in the sense we ordinarily use that word. Yet if we allow that the single most important task of living things is to pass on their genes (DNA) to as many offspring as possible, then viruses are very much a form of life. For the one thing viruses do have under their coats is genes; they do have DNA (or RNA, which the virus, once inside a cell, can convert into DNA). In fact, viruses are nothing more than DNA (or RNA) wrapped in a few strands of protein. And by the criterion of reproductive capacity, pound for pound viruses may be the most efficient biological entities around. The fact that they must infect a living cell to reproduce should not be held against them. In getting someone else to do most of the work for them, they might well be viewed as among the most successful of all life forms.

However we view them, viruses do strip the definition of life to its barest essentials. For example, viruses raise some intriguing questions about the very act of reproduction. Humans ascribe all sorts of noble reasons to their own reproductive efforts. Having children is variously held as the highest expression of the love between a man and a woman, an expression of confidence in the future of the race, and the central experience of human life. Rarely if ever would we describe our reproductive activities in terms of some common biological imperative to pass on DNA.

Higher-order reasons for generating offspring might even be extended to creatures other than ourselves. We can imagine an element of rational reproductive will among many of the animals in our environment - horses, say, or eagles, or cats and dogs. We readily recognize their courting and mating practices; we admire their devotion to their young. But if we were to let our minds wander to the reproductive activities of lower animals like starfish or molluscs or worms, ideas about reproductive will are apt to be replaced by images of blind, mindless mating impulses. By the time we got to something like bacteria in our considerations, we would probably be at a loss to imagine what could possibly be driving them to reproduce. Love of their offspring? Belief in the future of their race? On the other hand, we would at least view them as living things, subject to whatever reproductive imperatives are involved in the propagation of life.

But what about viruses? What could possibly drive a strand of DNA wrapped up in a handful of inert proteins to want or need reproduce itself? Where does that reproductive imperative - for surely it is that - come from? What, if anything, governs it?

These questions bring to mind an entirely hypothetical but nonetheless very interesting situation I heard described many years ago. It may ultimately help us to understand, or at least appreciate, the dilemma posed by viruses. In this scenario, we are asked to imagine the following. A world-famous university neurosurgeon, renowned for his ability to remove certain malignant tumors in the deepest recesses of the brain, one day learns that he himself has exactly such a tumor, in just such a place - the brainstem. At first he panics, for he knows the tumor is fatal, and he also knows that no one else in the world can remove the tumor without very likely killing him. But then, in a brilliant creative flash, he realizes that under the right conditions - with a bit of practice and a little help from his friends - he can probably remove the tumor on his own. The brain has no pain receptors; if he can get someone to open a portion of his skull under local anesthetic, then by using appropriate combinations of mirrors and surgical instruments, he should be able to perform the difficult surgical procedure himself.

After a few weeks of practicing with lights and mirrors, and running his assistants through endless drills, he is ready to go. The operation is long and difficult. Opening the skull was more painful than he thought. As familiar with the operation as he is, in the end he can't quite watch as the whining saw cuts into his own flesh and bone. He waits impatiently as his assistants lay back the skull flap and gently push apart the various layers of the brain to expose the tumor - the "easy stuff" he knows they are qualified to do. Finally, when all is ready, he picks up the scalpels and various probes from the tray in front of him. Closing his eyes for a moment, he mentally runs through the ensuing steps, sensing in his hands and in his mind's eye the necessary reversal of hand movements he has practiced for mirror-image surgery. He opens his eyes, takes a deep breath, and begins. Two hours later, he indicates by a wave of his scalpel that he has finished. The concentration required to prise the tumor from surrounding brain tissue without harming the brain itself has exhausted him completely. When he finally drops the offending tumor into the surgical specimen pan, he almost immediately falls into a deep sleep. His assistants drain and close the wound, and stitch his skull back together. To the great relief of everyone involved in this strange enterprise, the surgeon wakes the next day, and his previous symptoms rapidly disappear. It is clear the operation was a success.

Such a story, if true, would instantly be converted into several books, a TV docudrama, and very likely a movie. Our surgeon would be feted repeatedly by adoring medical groupies, and invited to speak before the American Medical Association. The best and the brightest young surgical residents would compete fiercely to get into his neurosurgery service at the university. But in focusing on the human and medical drama of this astounding achievement, we would miss an opportunity to take a fascinating look into what we might call the ultimate abyss of biology.

Let us go back over this episode from a purely biological point of view. In the movie, it will be implied that our surgeon-hero brilliantly deduced that he had a life- threatening tumor in his brain and decided on a bold course of action to remove it. But in reality, was it not the brain itself that made the diagnosis and mapped out the course of action? The brain, using information supplied to it during many years of medical education and training, was able to interpret correctly certain data it had acquired about its own condition. Using the eyes and ears feeding into it, consulting its data banks and employing its own capacity to reason, it determined that some of its cells had become cancerous. The brain knew it was going to die. The initial jolt of this recognition - what else can we say of it? it was a recognition - triggered a release of neuroendocrine hormones that caused the rest of the doctor to panic.

But then the brain realized that it had all the information it needed to rescue itself from extinction; it could, in fact, repair itself. The doctor it inhabited was equipped with an excellent set of hands and fingers that the brain could control with exquisite precision. The brain directed the rest of the doctor to set up a series of lights and mirrors so that it could use other input sensors - the eyes - to guide those hands and fingers through the required sequence of manipulations. It knew that it would have to remake certain of its connections to get the hands and fingers to perform the needed manipulations correctly, so it directed the doctor to practice while it studied the reaction and rewired itself. And when it was all done, the brain accomplished exactly what it set out to do - it saved itself from certain death.

In casting about for an explanation of this peculiar yet highly directed form of behavior, it would not be unreasonable to ask what made the brain behave in just this fashion, at just this time. Why did it want to survive? What does it even mean to say that a brain, in and of itself, could "want" something? But can we really doubt that all of the perceptions and reactions described above were carried out in the brain, and the brain alone? Could any other part of the body have perceived and reacted in the same way? No. Simply and finally, no.

So here we have this kilogram or so of pale, mushy tissue directing a remarkable sequence of reactions designed to save itself. Why? What drove it? In trying to answer this question, some biologists - cellular biologists - would take the level of analysis down one notch. After all, they would say, a brain is composed of cells; so in the end it must be individual cells that have the will to survive. This would not be impossible to imagine; single-cell monerans and protists are equipped with a variety of responses to assure, or at least enhance, their own survival. For example, individual cells living on their own can detect noxious substances in their environment and move away from them or retreat into a state of cryptobiosis. They can produce substances that kill or otherwise neutralize other single cells that can kill or otherwise neutralize them. These primitive cells (which certainly do not have brains) show a definite "will" to survive, so why shouldn't brain cells? If we are, in a sense, the biological heirs of these cells, perhaps some manifestation of a will to survive in our own cells is simply part of our evolutionary inheritance.

But other biologists - molecular biologists - would want to drop to an even more fundamental of analysis. Without doubt, every single action of a cell is directed by its DNA. Like a hologram, every cell of the body has embedded in it a DNA image of our complete biological selves. If every action of a cell is guided by its DNA and nothing else, it is hard to escape the conclusion that it wasn't really the brain that sensed approaching extinction in this little fantasy, nor even the brain’s cells. It must have been DNA.

Which brings us back to viruses. Viruses have certainly been on this planet much longer than human beings. Their ability to survive and reproduce is abundantly clear. In interpreting our own lives and deaths, humans tend to spin elaborate stories about love and free will. Here we stand, complex beings filled with emotions, dealing as best we can with biological imperatives we don't always understand. We are nurtured and we grow; we love, marry and have children, whom we in turn nurture and raise to become sentient adults. And there stands the virus, a few proteins wrapped around a single strand of DNA. This smallest of all biological entities is endowed with an incredible drive to reproduce itself. This minute speck, ten thousand or more times smaller than a bacterium, straddling the line between the living and the nonliving, can lay waste to a human being in a matter of days. In forms like the Ebola or Marburg viruses, or HIV, it has the potential to wipe out a significant portion of the human species. All this as it follows its destiny to reproduce itself, over and over and over again. A destiny written into a simple strand of DNA.

Is this the end of our quest to understand life and death, this double strand of four nucleic acids combined into a seemingly endless string of hieroglyphics? Embedded in this hologram are instructions specifying the composition and, ultimately, the exact placing of every molecule involved in the pure structure of a cell, the structure that interacts with ambient energy and food and oxygen to allow the cell to carry out its mission. And what is that mission? It is nothing less, and nothing more, than to facilitate copying and transmission of the DNA itself to the next generation. Our own DNA seems a bit less sure of itself than viral DNA; it makes a hundred trillion copies of itself - one set for each cell in the body - to ensure the transmission of just a few copies to the next generation. And then it directs the destruction of the other hundred trillion copies. And we die.

What drives DNA to reproduce itself? Why should it bother? What drives a lifeless, unfeeling virus to make more viruses? Why should a brain cell co-opt an entire doctor to save a tiny bit of DNA? This truly is where biology tapers off into pure chemistry and the thread of our existence disappears. This is the edge of the biological abyss, where the energy that permeates the universe interacts with structure to produce life. It is at this interface that we see both sides of ourselves, and where human beings sometimes see the face of God.

And a final thought……..

Our minds have come to regard our bodies as something more than a fancy vehicle for nurturing and transmitting DNA, and have made us unwilling to let reproduction be, as it is for all other living creatures, our only imperative, our only impact on the world in which we live. We have become thinking creatures who think about a great deal more than just our DNA. But the human mind is not the power that drives the universe. Whether we like it or not the mind, as brain, is driven ultimately by DNA, this bizarre molecule that is in turn driven - mindlessly, we presume; yet somehow desperately - to reproduce itself.

So are we simply being used by DNA for its own selfish ends? Perhaps. To paraphrase an old biological saw, a human being is just a germ cell’s way of making another germ cell - as is a cockroach; as is a cabbage. This is not a very flattering way to explain ourselves to ourselves. We want so desperately to be more than just a vehicle for DNA, and at least transiently we are. Yet somatic cells will die at the end of each generation, whether they are part of an insect wing or a human brain. We may come to understand death, but we cannot change this single, simple fact: in the larger scheme of things, it matters not a whit that some of these somatic cells contain all that we hold most dear about ourselves; our ability to think, to feel, to love - to write and read these very words. In terms of the basic process of life itself, which is the transmission of DNA from one generation to the next, all of this is just so much sound and fury, signifying certainly very little, and quite possibly nothing.