Origin of Life

How the Globe Was Stocked With Life

Ever since man began to think in the connected way that follows self-consciousness, he has pondered, with a mixture of fear, reverence, and curiosity, on the nature of life and its origin. The world in which he found himself was a vast mystery which, very crudely at first, he sought to penetrate. All his paths of thought led him circling back to himself as the greatest mystery of all. He struggled with the problem for thousands of years, framing fanciful guessworks, erecting elaborate structures of logic on foundations of error, emotion, and presumption, fashioning beautiful fables and theories (and waging wars to compel other men to accept them), yet found no better solution than that life must be a gift from some unknown, perhaps unknowable, source. Even lately, learned philosophers, such as Helmholtz and Kelvin, supposed it brought to the earth (in germs) by meteorites—fragments of exploded planets that had borne life before they went to destruction; or, like Arrhenius, postulated an impalpable dust, or "panspermia," scattered through all space and borne from the atmosphere of one planet to another. But all such hypotheses only threw the question of origin one step further back.

Meanwhile, beginning a few hundred years ago, when greater privilege of inquiry became possible in a jealous society, naturalists had tried to attack the problem from a new angle. They asked themselves whether they might not, by intensive study of living things, find the quality of life itself, hoping that if that could be done the source of it might be disclosed. In their earnest work they constantly improved their methods and their instruments, and so penetrated deeper and deeper into the constitution of plants and animals, until at last they found the ultimate particle in the cell and discovered living things so simple that they consisted of one cell alone; but why that microscopic particle was alive, while the grain of crystal beside it, or the drop of water in which it swam, was not  alive, remained unexplained.

Thereupon some of the naturalists fell back into the ranks of the speculative and religious persons who were content to believe the endowment of the world with life an act of a Divine Creator—something above and outside of nature as otherwise manifested; others asserted an equivalent but more materialistic doctrine that they styled "spontaneous generation," which presently was shown to be untrue, at least in the way they formulated it; and a third group confessed that they did not know whence life came, nor were they much concerned to know.

Life Constantly Originated By Nature's Productive Energy

This quest having failed—although it had taught much by the way—the chemists, who had been making marvelous discoveries in the inorganic lifeless half of nature, undertook a far more serious exploration of the organic living half. You have interpreted very fully, they told the naturalists, the forms, and structure, and functions of organisms, but can get no further; now let us chemists try whether we cannot find the principle of life by analyzing the substance  of living things.

Profiting by their experience, they turned to the colloids in hope of a clue. A colloid is a substance that shows no power of crystallization, and is composed of molecules united by their own affinity, and not by atomic affinity. They have a gelatinlike nature or composition, although varying greatly in chemical composition and general character. They differ widely in stability, for instance, some being easily upset by a change in conditions; and this peculiarity is of great importance in relation to the phenomena of life, for colloids enter largely into the composition of all living bodies, but always in a delicately balanced union with crystalloids. "The colloid is in fact," declared Thomas Graham, who first investigated its properties, "a dynamical state of matter; the crystalloid being the statical condition. The colloid possesses Energia. It may be looked upon as the probable primary source of the force appearing in the phenomena of vitality."

Now, many of the properties of inorganic colloids approximate those found in living structures, which appear to be "alive" by reason of the conversion of the energy of the sunlight into the chemical energy of their constituent (organic) colloids. The agent in this conversion is the green substance chlorophyll in the cell or cells of the plant; and, directly or indirectly, all the energy in living things arises from this one source, transmuted by this one transformer. Yet chlorophyll is far too complex a substance to arise as a first step from inorganic matter, even where conditions are suitable for life to appear; and the spontaneous production of such a thing as a bacterium would not solve the problem, for the new-born cell would have no organic food, and must at once perish. In an utterly lifeless planet inorganic colloids must first develop, and in time one of these must begin to evolve not a living cell, or anything so complex as a bacillus, but something in the way of a molecule holding a higher store of chemical energy than anything before it. Later such colloids, perhaps uniting with others, would begin to condense and form more complex organic molecules, and finally effect unions with crystalloids. Thus would organic complexity gradually be led up to, chlorophyll brought into being, and life appear. One of the foremost of the biochemists, Prof. Benjamin Moore, of the University of Liverpool, has summed this up picturesquely:

"It was no fortuitous combination of chances, and no cosmic dust, which brought life to the womb of our ancient Mother Earth in the far-distant Paleozoic ages, but a well-regulated orderly development, which comes to every mother earth in the universe in the maturity of her creation when the conditions arrive within the suitable limits. Given the presence of matter and energy forms under the proper conditions, life must come inevitably.... If this view be the true one, there must exist a whole world of living creatures which the microscope has never shown us, leading up to bacteria and the protozoa. The brink of life lies ... away down among the colloids, and the beginning of life was not a fortuitous event occurring millions of years ago and never again repeated, but one which in its primordial stages keeps on repeating itself all the time and in our generation. So that, if all intelligent creatures were by some holocaust destroyed, up out of the depths in process of millions of years intelligent beings would once more emerge."

That is to say, life arose through a recombination of forces preexisting in the cosmos, and the fact was but a step in the evolutionary process. "Such evolution," the American biologist, Henry Fairfield Osborn, declares with emphasis, "is essentially constructive, and ... is continually giving birth to an infinite variety of new forms and functions which never appeared in the universe before. It is a continuous creation or creative evolution. Although this creative power is something new derived from the old, it presents the first of the numerous contrasts between the living and the lifeless world."

Life's Borderland

Although in some respects a deceptive resemblance may appear between the living and the nonliving, the distinction is definite. Living bodies, plant or animal, are made up of protoplasm, which, although mineral in substance, consists of a combination never found in the mineral kingdom. It gives to the body containing it the power of growth, and this growth is by additions from within. Minerals may increase in size, but only by additions from without. The prime characteristics of living organisms is that they reproduce their kind, given favorable conditions. Minerals never do so. A correlative of life and growth is death, but minerals never die. In the course of its career every animal or plant, in proportion to its need or the degree of complexity of its organs, develops within itself characteristic compounds, such as albumin, gluten, starch, cellulose, fat and other chemical results, not a trace of any of which is to be found in rocks or soil, or in the water or in the air. No distinction in nature is so absolute as that between the inorganic and the organic realms, the nonliving and living things, so far as our senses can perceive them.

When, however, we consider the two prime divisions of the living world—animal and vegetable—so diverse in their higher developments, we find them springing from the same base in a single cell of almost structureless protoplasm, and so alike in this simplest form as to be in some cases indistinguishable—mere drops of living matter whose functions are so limited that they present no discriminative characteristics. Indeed, marking a definite boundary between animals and plants may be difficult in cases much higher in the scale than these primitive globules of protoplasm.

A fundamental distinction between plants and animals as we now know them is the exclusive possession by plants of the green substance chlorophyll, by the presence of which their food is transformed under the influence of sunlight into vital energy in a manner essentially different from that by which animals assimilate their substance. Chlorophyll is a complex, nitrogenous, colloidal substance, produced by and always associated with, protoplasm, and related to the coloring matter of the blood of animals. It is restricted to plants, and usually resides only in definite portions of the cell; yet we have good reason for believing, as Prof. William F. Ganong tells us, that our present green plants were preceded in time by a colorless kind of the utmost simplicity, and without chlorophyll, which yet could make their own food from carbon dioxide and water by using the energy of chemical oxidation of soil-minerals in place of sunlight. "We have precisely such chemosynthetic organisms, a kind of soil bacteria, still living on the earth at this day; and they are doubtless the lineal descendants of the ancient forms, which probably lived in the mud of shallow seas that may be full of them yet." These ancient chemosynthetic organisms were neither animal nor plant, but both and between. They must have expanded, varied, evolved, thus originating a great many branches, most of which perished.

Now, from this biochemical borderland of life, let us turn our attention to the living world as we know it to-day, or as preserved for us in the "record of the rocks," pausing only to fix well in our minds the main distinctions between animals and plants. Plants have no special organs for digestion or circulation, nor any nervous system. Most plants absorb inorganic food, such as water, carbonic acid gas, nitrate of ammonia, phosphates, silica, etc. No animal swallows any of these minerals as food. On the other hand, plants manufacture from such materials the food on which animals exist, by the production and storage in their tissues of starch, sugar, and nitrogenous substances. The two kingdoms supplement one another. They are mutually dependent, and probably originated simultaneously.