What Is Life?

What is life?" The question has been asked innumerable times but has been answered to the satisfaction of few. Science is based on the experience that nature gives intelligent answers to intelligent questions. To senseless questions, nature gives senseless answers - or no answers at all. If nature has never provided an answer to this question, perhaps something is wrong with the question.

The question is wrong indeed. It has no sense, for life in itself does not exist. No one has seen or measured life. Life is always linked to material systems; what man sees and measures are living systems of matter. Life is not a thing to be studied; rather, "being alive" is a quality of some physical systems.

A look at the living world reveals an incredible variety of shapes, sizes, forms, and colors. There seems to be an infinite variability among living systems. How can man approach such complexity? How can he ask intelligent questions?

One key to an intelligent approach may be the simple fact that things can be put together in two different ways: randomly or meaningfully. Things put together in random fashion form a senseless heap. Nine persons selected at random and placed together probably will form nothing more than a slightly puzzled collection of nine individuals. Nine persons selected and combined in a meaningful fashion may form a championship baseball team. The whole in this case is more than the sum of its parts - it is what is called organization.

If an atomic nucleus is combined with electrons, an atom is formed. This atom is something entirely new, quite different from electrons or nuclei alone. When atoms are combined, molecules are formed. Again, a new thing is generated with strikingly different qualities. Smaller molecules - say, amino acids - may be combined to form a "macromolecule" - perhaps a protein. This macromolecule has a number of amazing qualities. It demonstrates self-organization - the ability to create more complex, higher structures. It may act as an enzyme to speed up a particular chemical reaction, or it may act as an antibody to neutralize the effects of some other specific protein molecule. Proteins can be created in a literally inexhaustible variety of forms, each with its own qualities.

Macromolelcules may be combined to form small "organelles", such as mitochondria or muscle fibrils. When they are combined, the result is a cell - the unit of life, the miracle of creation - capable of reproduction and of independent existence.

The more complex the system, the more complex its qualities. Organs may be built from cells; from organs may come an individual organism, such as a human being. Individuals in turn may be combined to form societies or populations, which again have their own rules. At each level of complexity are new qualities not present in the simpler levels. The study of each level yields new information for the biologist.

The history of biology has been marked by a penetration into ever smaller dimensions. In the sixteenth century, Vesalius was dependent on his unaided eyesight for his study of the human body. In the following century, the optical microscope led to the discovery of many new details of structure. Marcello Malpighi observed the capillary vessels that complete the cycle of blood circulation and showed that even such tiny insects as the silkworm have an intricate internal structure. Anton van Leeuwenhoek described blood cells and the compound eyes of insects. Robert Hooke described the cellular structure of plants.

As microscopes were improved, more and more details of structure were described. By the nineteenth century, it was becoming clear that all complex organisms are composed of semi-independent units called cells. The major structural features of cells were established. Bacteria were discovered and studied.

In this century, the electron microscope has taken the scientist down to molecular dimensions, and he has learned to observe with x-rays as well as with visible light. Organic chemistry was established in the nineteenth century, and by the beginning of this century, it was clear that this approach could be applied to the study of living systems. Biologists have had to learn a new anatomy - the anatomy of molecules. Chemists and physicists have penetrated the atom, first finding the elementary particles and then moving still deeper into the realm of wave mechanics. The discovery of the wave properties of the electron has given a deep insight into the nature of biological reactions.

As scientists attempt to understand a living system, they move down from dimension to dimension, from one level of complexity to the next lower level. I followed this course in my own studies. I moved from anatomy to the study of tissues, then to electron microscopy and chemistry, and finally to quantum mechanics. This downward journey through the scale of dimensions has its irony, for in my search for the secret of life, I ended up with atoms and electrons, which have no life at all. Somewhere along the line, life has run out through my fingers. So, in my old age, I am now retracing my steps, trying to fight my way back toward the cell - the organism.

I have concluded that life is not linked to any particular unit; it is the expression of the harmonious collaboration of all. As I descended through the levels of complexity, I studied simpler units and found myself speaking more and more in the language of chemistry and physics.

J. F. Danielli has shown that the subcellular organs of various cells are interchangeable. They can be transferred from one cell to another, much as organs can be transplanted from one human individual to another. The parts of the cell have no individuality. The quality of individuality resides in the higher organization - in the cell or the individual.

No one yet knows the higher principle that holds a cell together. Perhaps the answer will be found in irreversible thermodynamics. The good working order of a living cell may correspond to a stable state with a high probability of occurrence. Perhaps some new principle - as yet undiscovered - keeps the cell together. Living systems do not only maintain their good working order but they all tend to improve it, to make the working structure more complex. When the fundamental principle that holds the cell together is found, perhaps we will then also understand what brought together the first living system and understand what drives living systems toward self-perfection.

Scientists know today that rather complex molecules - amino acids, nucleic bases, even macromolecules - can under certain conditions be built without intervention of living systems. They are still seeking the principle that brought