Origin Of Life
( Originally Published 1909 )
THE discussion of the origin of life is introduced by J. Arthur Thomson, of Aberdeen University, in 'The Science of Life' with the following words: "If it were the object of this book to give a statement of the established facts of biology, our discussion of the origin of life might be condensed into a single sentence: We do not know anything in regard to the origin of life. The only certainty is a negative one there is no established case in which living organisms have arisen apart from parent organisms of the same kind."
There are two distinct questions connected with the origin of life: First, how did it first originate in the early eras of the world's history? and, second, does life to-day originate spontaneously in inorganic matter? It seems best to consider these separately. Professor Max Verworn, of the University of Jena, gives a good summary of the various theories concerning the origin of life, and it is from his 'General Physiology' that some of the following illustrations have been taken.
The origin of life upon the earth is a first and leading problem. The idea that the earth was once in a highly heated condition is accepted in modern science. And this fact that it once was in a condition in which the temperature was enormously high and not a drop of water existed upon it, in short, a condition in which the vital conditions that are now regarded as indispensable to the existence of organisms were wanting, will always be an important factor with which all speculations upon the origin of life upon the earth must deal. Obviously in that highly heated condition life in its present form, at least, could not have existed. Then one of two things must have happened after the earth cooled down either inorganic matter must have become living matter or living matter must have come from other planets than this.
But if life came hither from other worlds, the interesting question as to the beginning of life remains. Helmholtz has said, "Organic life either has begun to exist at some one time or has existed for eternity." Evidently the two notions are mutually exclusive. Which affords the most reasonable basis of explanation? The idea that life has existed in the universe from eternity and has simply been transferred from one world to another is known as the theory of 'cosmozoa.' It was suggested by H. E. Richter (1865, '70 and '71), who assumed that among particles moving about in space, like meteorites, there are the germs of microscopic organisms capable of establishing life on the earth. Helmholtz and Sir William Thomson have discussed this question of the transference of living matter from other heavenly bodies to this earth and both term this view not unscientific. Helmholtz (1884) held that meteors which swarm everywhere in space might be the bearers of such germs in their cool interior cavities. He thought it a correct scientific procedure to question whether life may not be even as old as matter and its germs passed from world to world and developed wherever favorable conditions exist.
In the present condition of knowledge it is scarcely possible to obtain a direct contradiction of this doctrine and conclusive proof of its impossibility. This will be true so long as experience does not suffice to enable man to recognise as wholly impossible the transfer of protoplasmic germs of life from one world to another. But, altho direct contradiction of the doctrine is at present impossible, the thought that living substance has existed from eternity and has never originated from inorganic substance appears in the highest degree improbable.
Setting aside the 'cosmozoa' theory as improbable, and before considering the alternative view of the spontaneous generation of life from lifeless matter on the earth, mention should be made of Preyer's view that living matter is the primary thing and that lifeless matter has been derived from the living. According to this view, life must have existed when the earth was incandescent. Preyer fits his theory to this fact by giving to his conception of life a scope wider than that usually allowed, including not only present living matter but also incandescent liquid masses as they once existed. Life then had no origin ; it existed even in the beginning of the material universe. In fact, the view seems to identify life with motion. Evidently the language used constitutes the chief difference between this and the doctrine that living matter as now recognised was spontaneously generated from matter customarily termed lifeless. Whether from primeval conditions incandescent matter, which from our usual standpoint would certainly be considered lifeless, was really living and separated out that which we call lifeless or whether it was lifeless with the power to evolve into living matter are questions of greater metaphysical flavor than of direct interest in the biological science of to-day. In either case the original incandescent matter must have possessed the potentiality of evolving and differentiating into what is now recognised as living and lifeless matter. It matters little whether in philosophical moods it is sought to establish the primary vital force, for after all, as has been shown, vital force is not unique among the forces of the universe.
One of the most suggestive works discussing the origin of life from lifeless matter on the earth is by the famous German physiologist Pflüger (1875). He discussed the problem from the standpoint of physiological chemistry and follows it out far into detail. The essential point of Pfluger's investigation is constituted by the chemical characteristics of proteid as that substance with which life in its essentials is inseparably united. There exists a fundamental difference between dead proteid, as it occurs e.g., in egg albumen, and living proteid, as it constitutes living substance; this difference is the self decomposition of the latter. All living substance is continually being decomposed, in some degree spontaneously and more through outside influences, while dead proteid under favorable conditions remains intact for an unlimited time.
Further, Pflüger assumes on scientific grounds that the presence of cyanogen in living matter is responsible for the characteristic properties of living proteid, especially its great powers of decomposition. From this he concludes that the beginning of organic life was in cyanogen. Hence the problem of the origin of living substance culminates in the question: How does cyanogen arise
Here, organic chemistry presents the highly significant fact, that cyanogen and its compounds, such as potassium cyanide, ammonium cyanide, hydrocyanic acid, cyanic acid, etc., arise only in an incandescent heat e.g., when the necessary nitrogenous compounds are brought in con-tact with burning coal, or when the mass is heated to a white heat. "Accordingly, nothing is clearer than the possibility of the formation of cyanogen compounds when the earth was wholly or partially in a fiery or heated state." Moreover, chemistry shows how the other essential constituents of proteid, such as the hydrocarbons, the alcohol radicals, etc., can likewise arise synthetically in heat.
"It is seen," says Pflüger, "how strongly and remarkably all facts of chemistry point to fire as the force that has produced by synthesis the constituents of proteid. In other words, life is derived from fire, and its fundamental conditions were laid down at a time when the earth was still an incandescent ball. If now we consider the immeasurably long time during which the cooling of the earth's surface dragged itself slowly along, cyanogen and the compounds that contain cyanogen and hydrocarbon substances had time and opportunity to indulge extensively their great tendency toward transformation and polymerization and to pass over with the aid of oxygen, and later of water and salts, into that self destructive proteid, living matter."
Pflüger thereupon summarizes his ideas in the following sentences: "Accordingly, I would say that the first proteid to arise was living matter, endowed in all its radicals with the property of vigorously attracting similar constituents, adding them chemically to its molecule, and thus growing ad infinitum. According to this idea, living proteid does not need to have a constant molecular weight; it is a huge molecule undergoing constant, never ending formation and constant decomposition, and probably be-haves toward the usual chemical molecules as the sun behaves toward small meteors.
"In the plant, living proteid simply continues to do what it has always done since its origin i.e., regenerate or grow; wherefore I believe that all proteid existing in the world today was derived directly from the first proteid."
This idea of Pflüger's in essentials is generally accepted, for most present day biologists prefer to think of life as having originated directly from substances usually regarded as lifeless and of all existing living proteid as having descended in direct continuity from the first proteid. Moreover, some biologists follow Helmholtz and others in thinking that the first proteid may possibly have originated in some other part of the universe, but astronomy and geology offer good reason for believing that living matter might have originated on the earth when in its evolution to its present state conditions became right for its development.
However, notwithstanding all the speculations concerning the subject, it must be recognised that the problem is one of metaphysics rather than of natural science. The ordinary methods of scientific investigation are not applicable to the problem and one can only theorize as to the basis of life as it is known. But there cannot be any certainty that life in its beginning, under possibly vastly different conditions from those obtaining today, possessed the distinctive properties discovered in it by modern science.
That master of modern philosophical biology, Thomas H. Huxley, discussed the origin of life in his Presidential Address before the British Association for the Advancement of Science, forty years ago, and his words, while expressing the' ideas outlined above, stand high among the statements of the philosophical problems of biology. "Looking back through the prodigious vista of the past," he writes, "I find no record of commencement of life, and therefore I am devoid of any means of forming a definite conclusion as to the condition of its appearance. Belief, in the scientific sense of the word, is a serious matter and needs strong foundations. To say, therefore, in the admitted absence of evidence, that I have any belief as to the mode in which the existing forms of life have originated, would be using words in a wrong sense.
"But expectation is permissible where belief is not; and if it were given to me to look beyond the abyss of geologically recorded time to the still more remote period when the earth was passing through physical and chemical conditions which it can no more see again than a man can: recall his infancy, I should expect to be a witness of the evolution of living substance from nonliving matter. I should expect to see it appear under forms of great simplicity, endowed, like existing fungi, with the power of determining the formation of new living matter from such matters as ammonium carbonates, oxalates and tartrates, alkaline and earthy phosphates, and water, without the aid of light. That is the expectation to which analogical reasoning leads me; but I beg you once more to recollect that I have no right to call my opinion anything but an act of philosophical faith."
The second question to be considered is that of spontaneous generation. The view that life originally began in nonliving matter i.e., was spontaneously generated, is commonly accepted by twentieth century biology. But it should be noted that "belief in the spontaneous generation of simple living matter in the early ages of the worlds history is quite different from the belief that even today new living matter originates spontaneously without the influence of preexisting living matter."
This idea that living things, including even animals as complicated as flies and frogs, originate directly from lifeless matter, long after the first origin of life, has been widely accepted and is believed even today by many unscientific people. It is to this supposed origin of living matter within the period of human history that the term 'spontaneous generation' ('archegony,' 'abiogenesis,' 'generatio spontanea' or 'aequivoca') is most commonly applied and few authors of articles on the subject have included discussion of the first origin of life. Obviously the fundamental problems would be the same, no matter whether the spontaneous appearance of life in lifeless mat-ter occurred in the beginning of all life or occurs to-day. But the first is entirely beyond the power of scientific investigation, while if life now originates spontaneously a critical application of the methods of 'modern science ought to prove it and to throw light on the method of origin. Investigators have therefore been timulated to test the truth of the theory and to look for the key which will unlock the mystery of the first origin of life.
A vast amount of critical work has been done with the result that the biologists of the Victorian era proved that life does not originate spontaneously in any of the cases claimed to have been observed. In other words, life does not now spontaneously originate in lifeless matter so far as is known. This does not mean that it cannot or does not originate in some unknown form. This is a possibility which biologists recognise, and so they stand in an open-minded attitude ready to witness the origin of life from lifeless matter and really somewhat disappointed in that this opportunity has not yet come.
The story of the theory of spontaneous generation is one of the most fantastic in all biology. Thomson says: "If the longevity of a belief were an index to its' truth, the theory of spontaneous generation should rank high among the veracities, for it flourished throughout twenty centuries and more. We cannot trace the history of the theory in all its details, but the story may be recommended to the psychological historian as a labyrinth of error, with glimpses of truth at every turn."
The belief in spontaneous generation is recorded in literature back as far as Anaximander (611-547 B.C.), He believed that eels and other aquatic forms are produced directly from lifeless matter. His pupil Anaximenes (588-524 B.C.) "introduced the idea of primordial terrestrial slime, a mixture of earth and water, from which, under the influence of the sun's heat, plants, animals and human beings are directly produced in the abiogenetic fashion," says Osborn in 'From the Greeks to Darwin.' Diogenes and Xenophanes, the first to recognise the true nature of fossils, also believed in spontaneous generation. Then came the "father of natural history," Aristotle (384-322 B.c.), who fostered this idea so strongly that it has persisted for more than twenty centuries. He taught that not only small animals, but even frogs, snakes and eels are produced spontaneously from mud.
Long after Aristotle, men found no difficulty in believing in cases of spontaneous generation which would now be rejected as monstrous by the most fanatical supporter of the doctrine. Shellfish of all kinds were considered to be without parental origin. Eels were supposed to spring spontaneously from the fat ooze of the Nile. Caterpillars were the spontaneous products of the leaves on which they fed; while winged insects, serpents, rats and mice were all thought capable of being generated without sexual intervention.
The development of embryology and the knowledge of the life-histories of plants and animals gradually set aside many supposed cases of spontaneous generation. A little observation showed that individuals of these species developed from eggs produced by parents of the same species. But it is interesting to note that certain philosophers, notably among them being Augustine (353-430), still held to spontaneous generation as occasionally happening in animals reproducing by the sexual method. According to Augustine, from the beginning there had existed two kinds of germs of living things: first, visible ones, placed by the Creator in animals and plants; and second, invisible ones, latent and becoming active only under certain conditions of combination and temperature. It is these which produce plants and animals in great numbers without any cooperation of existing organisms. This was a naturalistic way of explaining the sudden appearance of countless numbers of frogs, insects and other animals which to-day offers no difficulty, now that the remarkable fertility of animals is known.
Even a man like Cesalpino (1519-1603), who did some excellent botanical work, and had, long before Harvey, some clear ideas as to the circulation of the blood, "believed that frogs might be generated from the mud with the help of sunshine," says Thompson, "and even suggested similar origin of the aboriginal Americans. The botanists were no better than the zoologists. One of their favorite notions was that the green dust which grows in damp weather on trees and stones, which is now known to consist of unicellular Algae, such as 'Pleurococcus,' was a standing evidence of the genetic connection between the dead and the living, between the mineral and the vegetable; even Bacon of Verulam believed in the spontaneous origin of some higher plants, like thistles, from earth; and the Italian botanist Matthioli regarded the duckweed, whose leaf like shoots are so common on the surface of pools, as a condensation of the still water, and a starting-point for higher forms of plant life; while even Harvey continued to believe in spontaneous generation."
A scientific experiment to test spontaneous generation was first undertaken by Francesco Redi, a distinguished Italian physician and scholar. The origin of maggots from putrefying flesh had long been accepted as a clear case of spontaneous generation. Tyndall, in an article on spontaneous generation, writes of this as follows : "Lacking the checks imposed by fuller investigation, the conclusion that flesh possesses and exerts this generative power is a natural one. I well remember when a child of ten or twelve seeing a joint of imperfectly salted beef cut into, and coils of maggots laid bare within the mass. Without a moment's hesitation I jumped to the conclusion that these maggots had been spontaneously generated in the meat. I had no knowledge which could qualify or oppose this conclusion, and for the time it was irresistible. The childhood of the individual typifies that of the race, and the belief here enunciated was that of the world for nearly two thousand years."
To the examination of this very point the celebrated Francesco Redi addressed himself in 1668. He had seen the maggots of putrefying flesh, and reflected on their possible origin. But he was not content with mere reflection, nor with the theoretic guesswork which his predecessors had founded upon their imperfect observations. Watching meat during its passage from freshness to decay, prior to the appearance of maggots he invariably observed flies buzzing round the meat and frequently alighting on it. The maggots, he thought, might be the half-developed progeny of these flies.
"The inductive guess precedes experiment, by which, however, it must be finally tested. Redi knew this, and acted accordingly. Placing fresh meat in a jar and covering the mouth with paper, he found that, tho the meat putrefied in the ordinary way, it never bred maggots, while the same meat placed in open jars soon swarmed with these organisms. For the paper cover he then substituted fine gauze, through which the odor of the meat could rise. Over it the flies buzzed, and on it they laid their eggs, but the meshes being too small to permit the eggs to fall through, no maggots were generated in the meat. They were, on the contrary, hatched upon the gauze. By a series of such experiments Redi destroyed the belief in the spontaneous generation of maggots in meat, and with it doubt-less many related beliefs. The combat was continued by Vallisneri, Schwammerdam and Réaumur, who succeeded in banishing the notion of spontaneous generation from the scientific minds of their day. Indeed, as regards such complex organisms as those which formed the subject of their researches, the notion was banished forever, so far as accepted science was concerned." However, to this day many untutored persons firmly believe that dead horse-hairs placed in water transform themselves into horse-hair eels and that meat generates maggots and other forms of life.
In the latter half of the seventeenth century the great improvement of the microscope as an instrument of investigation paved the way to a new phase of the discussion of spontaneous generation. This came about because of the fact that the instrument brought into view a world of life formed of individuals so minute so close as it seemed to the ultimate particles of matter as to suggest an easy passage from atoms to organisms. Animal and vegetable infusions exposed to the air were found clouded and crowded with creatures far beyond the reach of unaided vision, but perfectly visible to an eye strengthened by the microscope. With reference to their origin these organisms were called 'Infusoria.' Stagnant pools were found full of them, and the obvious difficulty of assigning a germinal origin to existences so minute furnished the precise condition necessary to give new play to the notion of heterogenesis or spontaneous generation.
Many scientific men of that day took up the question of the origin of the microscopic organisms. A Scotch priest, Turbervill Needham (1750), showed that animalcules (Infusorians and the like) appeared even in decoctions which had been boiled and corked up. As we should now say, this result was due to imperfect sterilization and imperfect corking of the tubes; but it was used by Buffon, who was much interested in Needham's work, to bolster up a pet theory of his, that life resided in indestructible organic molecules, and that these were liberated after death or in decomposition as the aforesaid Infusorians or animalcules.
This result of Needham's was contradicted in 1777 by the Abbé Spallanzani who charged his flasks with organic infusions, sealed their necks with the blowpipe, subjected them in this condition to the heat of boiling water, and subsequently exposed them to temperatures favorable to the development of life. The infusions continued unchanged for months, and when the flasks were subsequently opened no trace of life was found. Spallanzani's flasks must have contained but little air and it was objected by the chemists, who had now discovered oxygen, that life could not be expected where this gas was more or less absent, and that the boiling process might irretrievably injure the 'organic molecules.'
Schultze and Schwann (1836, 1837) were thus led to make fresh experiments; they carefully boiled the infusions and supplied air which had been passed through red hot tubes or acids, no animacules appeared; they then sup-plied air which had not been so purified, and in the same infusions the animalcules appeared. Schwann's final conclusion was "that putrefaction is due to decompositions of organic matter attendant on the multiplication therein of minute organisms. These organisms are derived not from the air but from something contained in the air, which is destroyed by a sufficiently high temperature."
The next step in advance came in 1854, when Schroeder and Dusch did what is now so often done as a class experiment: they boiled infusions, and while the steam was coming off plugged the neck of the flask with cotton-wool. This allows the passage of oxygen, but keeps back germs ; and in most cases the sterilization is quite effective. In 1859 a book was published which seemed to overturn some of the best established facts of previous investigators. Its title was 'Héterogénie,' and its author was F. A. Pouchet, Director of the Museum of Natural History at Rouen, a strong believer in the theory of spontaneous generation. "Never," says Tyndall, "did a subject require the exercise of the cold critical faculty more than this one. To a man of Pouchet's temperament the subject was full of danger-danger not lessened by the theoretic bias with which he approached it."
Pasteur's work in chemistry and in special research in fermentation had prepared him for this investigation. He knew more than Pouchet as to the insidious ways of microbes ; he showed the weak point of his antagonist's experiments, and gained the prize offered in 186o by the Academy, for "well-contrived experiments to throw new light upon the question of spontaneous generation." Pasteur threw light on the subject by his study of the organized particles many of them living or dead bacteria which float in the air. He opened twenty sealed flasks containing organic infusions in the pure air of the Mer de Glace, and only one thereafter showed signs of life ; but eight out of twenty opened on the plains, and all of the twenty opened in town, developed germs. These and other experiments, carried out with a severity perfectly obvious to the instructed scientific reader, and accompanied by a logic equally severe, restored the conviction that, even in these lower reaches of the scale of being, life does not appear without the operation of antecedent life. Pasteur's brusque conclusion was that "spontaneous generation is a chimera."
These experiments by Pasteur laid the foundation for a long series of studies of micro-organisms by himself, Tyndall and others. Tyndall describes the famous experiment in which he proves that "not in the air, nor in the in-fusions, nor in anything continuous diffused through the air, but in discrete (organic) particles, suspended in the air and nourished by the infusions, we are to seek the cause of life" as follows: "Supposing an infusion intrinsic-ally barren, but readily susceptible of putrefaction when exposed to common air, to be brought into contact with unilluminable air (air freed from dust particles), what would be the result? It would never putrefy. Let a condensed beam be sent through a large flask or bolthead containing common air. The track of the beam is seen within the flask the dust revealing the light, and the light revealing the dust. Cork the flask, stuff its neck with cotton-wool, or simply turn its mouth downward and leave it undisturbed for a day or two. Examined afterward with the luminous beam, no track is visible ; the light passes through the flask as through a vacuum. The floating matter has abolished itself, being now attached to the interior surface of the flask. Were it the object effectually to detain the dirt, that surface might be coated with some sticky substance. Here, then, without 'torturing' the air in any way, is a means of ridding it, or rather of enabling it to rid itself, of floating matter.
"We have now to devise a means," he continues, "of testing the action of such spontaneously purified air upon putrescible infusions. Wooden chambers, or cases, accordingly are constructed, having glass fronts, side-windows and backdoors. Through the bottoms of the chambers test-tubes pass air-tight; their open ends, for about one-fifth of the length of the tubes, being within the chambers. Provision is made for a free connection through sinuous channels between the inner and the outer air. Through such channels, tho open, no dust will reach the chamber. The top of each chamber is perforated by a circular hole two inches in diameter, closed air tight by a sheet of india rubber. This is pierced in the middle by a pin, and through the pinhole is pushed the shank of a long pipette, ending above in a small funnel. The shank also passes through a stuffing-box of cotton-wool moistened with glycerine; so that, tightly clasped by the rubber and wool, the pipette is not likely in its motions up and down to carry any dust into the chamber.
"The chamber is carefully closed and permitted to remain quiet for two or three days. Examined at the beginning by a beam sent through its windows, the air is found laden with floating matter, which in three days has wholly disappeared. To prevent its ever rising again, the internal sur-face of the chamber was at the outset coated with glycerine. The fresh but putrescible liquid is introduced into the six tubes in succession by means of the pipette. Permitted to remain without further precaution, every one of the tubes would putrefy and fill itself with life. The liquid has been in contact with the dust-laden air outside by which it has been infected, and the infection must be destroyed. This is done by plunging the six tubes into a bath of heated oil arid boiling the infusion. The time requisite to destroy the infection depends wholly upon its nature. Two minutes' boiling suffices to destroy some contagia, whereas two hundred minutes' boiling fails to destroy others. After the infusion has been sterilized, the oil bath is withdrawn, and the liquid, whose putrescibility has been in no way affected by the boiling, is abandoned to the air of the chamber.
"With such chambers I tested, in the autumn and winter of 1875-6, infusions of the most various kinds, embracing natural animal liquids, the flesh and viscera of domestic animals, game, fish and vegetables. More than fifty chambers, each with its series of infusions, were tested. many of them repeatedly. There was no shade of uncertainty in any of the results. In every instance we had, within the chamber, perfect limpidity and sweetness, which in some cases lasted for more than a year without the chamber, with the same infusion, putridity and its characteristic smells. In no instance was the least countenance lent to the notion that an infusion deprived by heat of its inherent life, and placed in contact with air cleansed of its visibly suspended matter, has any power to generate life anew.
"The argument is now to be clenched by an experiment which will remove every residue of doubt as to the ability of the infusions here employed to sustain life. We open the back doors of our sealed chambers, and permit the common air with its floating particles to have access to our tubes. For three months they have remained pellucid and sweet flesh, fish and vegetable extracts purer than ever cook manufactured. Three days' exposure to the dusty air suffices to render them muddy, fetid and swarming with infusorial life. The liquids are thus proved, one and all, ready for putrefaction when the contaminating agent is applied."
Many such experiments as these established beyond a doubt the fact that no known case of spontaneous generation occurs under the present conditions of life. 'Omne vivum e vivo' would correctly express the accepted view of the twentieth-century biologists, provided it be translated `all life from life' under known existing conditions, but probably life from the lifeless in its first origin on this earth or elsewhere.
That all living matter existing today has descended directly from preexisting living matter is the doctrine of `Biogenesis,' the rival of the dethroned doctrine of `Abiogenesis.' Observe that the doctrine of biogenesis refers simply to what is now happening and has been happening in all times of which we have strictly scientific records. The theory of biogenesis thus understood as the prevailing natural process will still stand even if, as seems probable, some lucky physiological chemist succeeds in synthesizing under artificial conditions new living matter, entirely independent of preexisting living matter. He will have done nothing more than repeat under unusual and artificially controlled conditions the processes which probably occurred when in the evolution of matter in the post incandescent ages of the earth living proteid, progenitor of all future organisms, first came into existence. So far as the future succession of organisms on this earth is concerned, it can-not even be imagined that living matter synthesized in scientific laboratories will play any part. The law of biogenesis, now established as firmly as that of gravitation, may be expected to stand as the very rock of ages in the science of biology.
Such is in outline the story of one of the greatest fallacies with which modern science has had to deal. But, strange to say, the establishment of the truth of biogenesis, which directly is of little importance to man, has laid the foundation for practical researches of a most momentous kind. To Pasteur and the other great generals in the last battles against the theory of spontaneous generation is due the honor of the establishment of the new science of bacteriology which in the last two decades has come to play such a mighty part in the development of modern life.