ONE of the most obvious questions about life is, Where does it begin? When a child first becomes inquisitive he rarely asks, ‘Who am I?’ in the manner of Socrates, but in practically every case he will ask his embarrassed mother, ‘Where do I come from?’ It seems that the question of life’s origin suggests itself to the human mind sooner than the question of its essence. The problem of life itself is too deep for the average person. He observes it daily. He takes it for granted. But that it must begin somewhere he can understand. Witness the commotion aroused by the Tennessee debate on whether life began by special creation or by evolution — commotion not only among the theologians and scientists directly interested, but among the common people of every walk of life. On the other hand discussions regarding the nature of life itself usually take place in the seclusive halls of big universities, and seldom are reported in the front-page columns of newspapers.
Man, being alive himself, has always taken a keen interest in all other living things around him. Among the earliest attempts at art and decoration by our caveman ancestors we find more images of horses and trees than of lifeless rocks and mountains. And throughout recorded history man has had his ideas regarding the origin of living things. He could not help but notice that living things were not all alike. Some were smaller and simpler in their make-up than others. He followed life down the scale to the smallest and simplest thing he could see, and in so doing he was led to the conclusion that life began spontaneously in filth and dirt. Beyond that point he found no sign of life, but only lifeless matter like rock and water and air. In the scale of things on this earth, therefore, life seemed to begin with the worms and moulds found in rotting and decaying substances.
No more was known about this subject until the beginning of our present scientific age. When we consider that 90 per cent of what we know we have learned through the medium of our eyes, it is not surprising that modern biology dates back only to the seventeenth century, when the compound microscope was discovered. This literally opened man’s eyes. The microscope made it possible for man to see things several hundred times smaller than his natural eyes had ever seen before. With the aid of the microscope it was discovered that all living things consist of cells of about the same size, but that large animals and plants are composed of a greater number of them than the small ones, as large buildings are constructed of more bricks and stones than are small buildings. The smallest animals, like amœbæ, and the smallest plants, like algæ, consist of only one cell. For many years these tiny creatures, found in the grime and slime of stagnant pools, were considered to be the lowest limit and therefore the beginning of life.
But in the last half of the nineteenth century Pasteur discovered bacteria. Bacteria are so much smaller than other cells that many of them can live and multiply inside of a single cell, like rabbits in a barn. Some bacteria are so small that even with the microscope one can hardly see them. It was soon noticed that bacteria were not all alike. Many species were found to exist. A few were disease-producing. Most of them were not only harmless but of great value — as, for instance, in breaking down dead animal and plant matter into useful soil for the growth of new vegetation. Bacteria vary in shape, the commonest being the spheres called cocci, the rods called bacilli, and the spirals called spirilla. They vary in size, but are all invisible to the naked eye.
Pasteur furthermore exploded the belief that life originates spontaneously during the process of fermentation and decay. He proved experimentally that every cell and every bacterium descends from a parent cell of the same variety, and he was unable to find any living thing springing from dead matter. Fermentation and decay he showed to be the result of the life activities of yeast cells and bacteria, and not the cause of such living things. Man had previously put the cart in front of the horse in that respect.
Bacteria were the smallest units of life the scientists could detect with the microscope. It had been hoped that a sufficiently powerful microscope could be constructed to permit still further investigation; but it was found that the human eye cannot perceive objects smaller than the wave length of light, and that limit had been reached. The hope of facing life at its very source seemed to be blasted. There still remained a gap between the bacteria and lifeless matter, an unexplored and alluring region of existence where scientists felt that life must begin. Darwin convincingly suggested that over a period of millions of years species of animals or plants could evolve from a lower to a higher order, even if biologists found that every cell descended from a like parent cell in the course of laboratory observation; because what is the human life span, and even the period of recorded human history, as compared with the millions of years of evolutionary development? Scientists have become more and more convinced that evolution is not only a thing of the past, a matter of history, but a going thing. Life is progressing right now. And if it is progressing all along the line, it should also be constantly beginning. So the problem of where life begins has had to be attacked from another angle than that of the microscope.
The chemists and physicists began to interest themselves in the problems of the biologist. They had methods of investigation in their bag of tricks with which the biologist was not so well acquainted. Living material, called protoplasm, was analyzed. It was found to consist essentially of a compound called protein, which could be split into less complicated molecules called amino acids. Starting from the other end of the scale of chemical complexity, they devised methods of synthesizing these amino acids, and even making some protein artificially. To be sure, they had to tax their brains to the utmost, because these substances are the most complex in chemistry; and the chemists are still a long way from having completed their job.
From the standpoint of physics, protoplasm was found to be a jellylike material, called colloid, the particles of which carry an electrical charge opposite to that of their environmental solution. The physiochemist now had visions of creating living substances. He seemed so close to it. Occasionally some enthusiastic reporter would tell the newspaper readers that the trick had been done. But up to the present time the chemists and physicists have not succeeded in getting farther than the lifeless protein molecules. At that point they also came to a blind alley. At that point in their study of lifeless matter, up the scale of complexity of molecules, they arrived at the same baffling gap which stopped the ambitions of the biologists in their study of living things on the downward scale. It became clear to all that there was a gap, yet all were convinced that life must begin in that gap.
Now gaps have been conquered before. The most interesting chapters in the history of science deal with such conquests of gaps. What can be more fascinating than the really true story of Neptune, that most distant and large planet of our own solar system? Leverrier, a French astronomer, noticed that Uranus was acted upon by something which nobody knew existed. He computed the attractions and repulsions so accurately that in 1846 Galle, a German astronomer, was able to point his telescope toward that gap and demonstrate the actual existence of a large planet. There was Neptune. He was not found by accident; Leverrier knew that he had to be just there. And in the field of chemistry, also, several gaps in Mendeléeff’s table of elements, arranged according to their atomic weights and other properties, have successfully been filled. Thus in 1869 three elements, scandium, gallium, and germanium, were discovered because they had been missing in the scale of Mendeléeff. The gaps into which they fitted had been known. And even the discovery of radium by Madame Curie and her husband was at least partially made possible by the knowledge of an unfilled gap in the series of elements.
Life begins somewhere and somehow in a gap between the lowest of a series of definitely living organisms, the smallest and simplest bacteria, and the highest of a series of lifeless chemical compounds, the proteins, which are the chemical basis of living protoplasm. At least as far as size, complexity of physical construction, and functional activity are concerned, it is in this gap that living things first appear to our senses.
In reading about evolution we are told that at a certain stage, many millions of years ago, life began to develop from the lifeless materials of our earth by the combining of certain chemical molecules under ideal conditions of moisture, atmosphere, and sunshine. After that, life evolved very gradually into higher and higher stages of complexity and function. One gets the idea that life started only once many ages ago. That may be the case. But if evolution is a going thing at the present time, — as biologists and sociologists say it is, — and if life to-day is progressing toward better quality, is it not reasonable to assume that evolution at the lower end of the scale should also be in operation, and that life is constantly beginning, constantly growing out of the lifeless physicochemical background?
It is a well-known fact that there is an enormous amount of life activity in the regions beyond the limits of our natural vision. The soil, the water, and even the air, as has been recently shown at Cambridge, are teeming with bacteria of various kinds. And bacteria can multiply faster in a few minutes than the human race has done in the period of recorded history. Now just beyond the bacteria lies the gap where life must begin to make its appearance in the series of things on our planet, starting with the electron and atom on the one end and ending with man on the other end.
Do we know anything about this gap between the lifeless and the living things? Yes, we do. Within the last few years certain discoveries have been made which are not as yet known to the average layman. Thanks to the invention of the ultramicroscope and to the perfection of bacteriological, physical, and chemical technique, a new field of knowledge has been opened up which for years had escaped the searching eyes of the scientists. While perfecting the methods of studying the smallest bacteria, laboratory workers discovered the ultramicroscope and the porcelain filter. And as a result of the discovery of these two instruments of research man got his first glimpse into that mysterious gap between the lifeless and the living.
We have said before that objects which are smaller than the wave length of light cannot be seen directly even through the most powerful microscope. But, if illuminated from the side, they can be seen, because each particle becomes a point of light reflection. Just as dust in the air of a room, otherwise invisible, can be seen in the sunlight shining through a crack in the side wall — an experience we all have had. Based on this principle, the ultramicroscope enables us to see things hundreds of times smaller than the smallest thing that can be seen through the ordinary microscope. And then there is the porcelain filter, which is used to separate the microscopically visible from the invisible. The latter pass through and are called filter passers. By using filters of different grades of porcelain we can measure the size of these filter passers.
Life has been discovered in material which goes through filters. This form of life is the smallest known to-day.
The first intimation that filtrable living things exist was the discovery in 1892 that tobacco mosaic, a disease of tobacco leaves, was caused by an invisible germ that escaped through the meshes of a filter. Since then many other diseases of plants, animals, and man have been found to be caused by filter passers. Among them are such common ones as dog distemper, footand-mouth disease, chicken pox, smallpox, and measles. Altogether almost a hundred filtrable living organisms are known to-day. Some of them are harmless, probably even useful — like, for instance, the bacteriophage, a filtrable virus discovered in 1917 by D’Herelle of the Pasteur Institute at Paris, which destroys certain diseaseproducing bacteria.
To-day there are many scientists actively working with the different varieties of filtrable viruses, and some of them, who are philosophically inclined, are beginning to consider these filtrable organisms the connecting link between the non-living and the living things of this world. For, as we mentioned before, when we ascend the series of non-living things from electron to atom to molecule, before we can continue with our series of living things, starting with bacteria, we come to a gap in continuity. In this gap we should expect to find something which is not quite as dead as a brick, or quite as alive as a sunflower. And, lo and behold, scientists are not in agreement as to the ‘aliveness’ of filtrable viruses. Now, it has been shown that filter passers are not alike, but can be divided into species, some lower and some higher. We find that the lower species, like the bacteriophage, resemble in many ways the enzymes and are nearer to what we should call the non-living. On the other hand we find that the higher species, like smallpox virus, are definitely alive, which means that they eat and grow and multiply, show signs of adaptation to environment, and can be cultured in the laboratory.
When filter-passing life was first discovered it was thought that it probably was a liquid form of life. But the ultramicroscope disclosed the fact that it occurs in units of definite size, and that the size is smaller as the characteristics of the species approach the non-living, and larger as they approach the living. The size of all filter passers, however, is as much smaller than that of bacteria as a mouse is smaller than a dog. It is believed that all filter passers are parasitic in nature, and that they cannot live independently of their hosts. In some cases, as in smallpox virus, the human cells act as the host. In other cases bacteria are the hosts, in which case we are reminded of the saying, ‘Great fleas have little fleas upon their backs to bite ’em.’ The fact that, among bacteria the smaller species live and multiply within the host cells, while the larger ones live outside the cells, together with the fact that filter passers apparently all live within the host cells, shows the close evolutionary relationship between the two and the immaturity of the little filter passers as far as their being independent living organisms is concerned.
Chemically, filter passers consist of protein as all other living things do. It is estimated that a unit filter passer consists of about three hundred molecules of protein compound. Each unit carries an electronegative charge. Exposure to heat permanently stops all manifestation of life among the filter passers as it does among all other living things. In other words, heat kills the filter passer. Cold, on the other hand, simply suspends the signs of life temporarily. Whether these tiny organisms are sentient, whether they are conscious, we do not know. But it is probable that any living thing, no matter how small, that knows its own habitat and pabulum and gets along in this world must have at least some consciousness and judgment. So when we take all known facts about these microscopically invisible things into consideration, we must come to the conclusion that they must be alive, some probably more so and some probably less.
Now, whether filter-passing organisms as we know them to-day are the smallest living things, we do not know. But they certainly fit into the gap between the largest and most complex non-living chemical molecule, the protein molecule, and the smallest and simplest living thing known until recently, the bacterium. The filter passer completes the series of units in nature, which starts with the electron and ends with man. Situated in the middle of the series, at the dividing line between the lifeless and the living, we find that it has certain attributes of each. If it is not the smallest and simplest living thing, then it must at least resemble it, because there is not enough room within the gap to allow for much else. At least in the light of present scientific knowledge, life begins with these filter passers to come to our attention as we ascend the scale of nature from electron to man. From some such simple origin the evolution of life on this earth at one time began. Or could it be that it is constantly beginning from something similar to these filter passers, even to-day?