EVOLUTION & THE SCIENTIFIC ACCOUNT OF THE ORIGINS OF LIFE
Evolution comes from the word evolve, which in early days meant twisting two scrolls so that one payed out, the other wound up the papryus. Today it still means about the same thing, a new popular theory replacing an old.
Some educators would have the basic tenets of science, as now taught, replaced with a novel doctrine called "Intelligent Design"
Last Friday, C-Span had two guests, one representing views of the Discovery Institute, the other that of Separation of Church and State, ably represented by Rev. Barry Lynn.
Their dialogue proceeded about as successfully as the current Hezbollah-Israili dispute, but fortunately didn't come to blows. However, just such nonsense can lead to blows, if economic issues become involved, like the late differences over abolition of slavery.
In fairness, I have copied the lead paragraph from Wiki-pedia on Intelligent Design, which won't please everybody, but since this is a self-generated encyclopedia, write it yourself!
>>>>>>>>>>>>>Intelligent?
Intelligent design (ID) is the concept that "certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection."[1] Its leading proponents, all of whom are affiliated with the Discovery Institute,[2] say that intelligent design is a scientific theory that stands on equal footing with, or is superior to, current scientific theories regarding the evolution and origin of life.[3]
An overwhelming majority[4] of the scientific community views intelligent design as pseudoscience[5][6] or junk science.[7] The U.S. National Academy of Sciences has stated that intelligent design "and other claims of supernatural intervention in the origin of life" are not science because they cannot be tested by experiment, do not generate any predictions, and propose no new hypotheses of their own.[8]
In Kitzmiller v. Dover Area School District (2005), a United States federal court ruled that a public school district requirement for science classes to teach that intelligent design is an alternative to evolution was a violation of the Establishment Clause of the First Amendment to the U.S. Constitution. United States District Judge John E. Jones III ruled that intelligent design is not science and is essentially religious in nature.[9]<<<<<<<<<<<<<<<<<<<<<<
It occurred to me that I should drag out my old book "Limitations of Science" which was authored in 1933 by J.W.N. Sullivan, who was limited as he has not had the last 70 years of one of the most productive scientific centuries known to me, and probably mankind. I discovered Chapter 4. "The Scientific Account of the Origins of Life" which I present below. Mind you Watson & Crick and their competent assistant Rosalind Franklin were probably in 1st grade when this book was written.
>>>>>>>>>>>>>>>>>>>>>>>J.W.N. Sullivan - Limitations of Science
About This Book
"At the present day," says J. W. N. Sullivan, "the scientific universe is more mysterious than it has ever been before in the history of thought. Although our knowledge of natural processes is greater than it has ever been, this knowledge is, in a way, less satisfactory, for in every direction we are faced by ambiguities and contradictions. Yet this state of affairs is not depressing; it is, on the contrary, extraordinarily stimulating. For we feel that our difficulties can only be resolved by man's imagination rising to the task of constructing radically new concepts. We have reached one of the great stages in the adventure of thought . . . We are required to see the universe with new eyes, and it is because it makes such demands and also holds out the promise of realizing them, that the study of science is so supremely worth while."
J. W. N. Sullivan sees present-day science as limited, but the potentialities of science, and the possibilities for the growth of human consciousness, as limitless. He traces the development of the various branches of modern science as aspects of an inter-related whole. He illuminates not only the facts of science, but the scientific spirit, the scientific method, as well. Perhaps, his most brilliant insights are into the moral and aesthetic values of science. "It is in its aesthetic aspect," he says, "that the chief charm of science resides." In his final valuation, Sullivan underlines the belief of many modern men of science that science gives us but a partial knowledge of reality and that, for example, our religious aspirations and our perceptions of beauty may not be the illusory phenomena they were once thought to be.
Mathematician, musician, philosopher, author of numerous books including one on Beethoven. J. W. N. Sullivan was named by Time as, "one of the world's four or five most brilliant interpreters of physics to the world of common men." He is regarded as one of the most accomplished men of his generation.
4. The Scientific Account of Origins
1
One of the most interesting questions that can be put to science is the question as to the origin of the present state of things. We are born into a world of inconceivable diversity. The mere varieties of material substance themselves defy enumeration. And even more unimaginable is the variety of living things, plants and animals. We ourselves, as has long been remarked, are fearfully and wonderfully made. The immediate scene of this panorama is the surface of a sphere of land and water, rotating on its axis, and circling round an immensely linger sphere of blazing gas. Attending it are other spheres which, judged by our standards, are completely meaningless, since they support no life, and have no bearings on ours. And the whole of this system, our sun and its planets, is, it appears, infinitely insignificant in the universe of matter. In every direction in space blaze countless millions of other suns, apparently without any reference whatever to our existence. Can we believe that this state of affairs always existed? If not, how did it come about?
It is probable that man has to reach a certain level of ease and culture before he can ask even this question seriously. For we cannot believe that the primitive cosmogonies, which asserted such things as that God took the sun, moon, and stars out of a box and hung them up, were intended as serious answers to a serious question. Some primitive peoples, however, took the questions a little more seriously, but not seriously enough to warrant any detailed examination of their theories.
The Greeks, however, elaborated a point of view which, with suitable modifications of detail, would still be held as a representative opinion. Plato says:
"The philosophers say that fire and water and earth and air all exist by nature and chance and none of them by art, and that the bodies which come next in order—the earth, sun, moon, and stars—have been created by means of these absolutely inanimate existences. The various elements are moved by chance and also by inherent forces according to certain affinities amongst them—of hot with cold, dry with moist, soft with hard, and according to all the other accidental mixtures of opposites which have of necessity happened. After this fashion has been created the whole of heaven and all that is therein, as well as all animals and plants and all the seasons. These come from these elements, not by any action of mind or of any God, or from art, but by nature and chance only."
This theory, that everything has come about by chance through the random action of "laws of nature," is probably still the most widely held theory amongst educated people. For many centuries, in Europe, this theory was opposed by the doctrine of special creation as taught in Genesis. Through the labours of modern scholars, however, the real meanings of the statements in Genesis have become so elusive that it would be difficult now to say precisely what the doctrine of special creation, as taught there, really is.
The first really scientific attempt to answer the question of the origin of things was published in 1796 by the French mathematician, Laplace, This was the famous Nebular Hypothesis. Its main idea had already been put forward by Kant but, owing to insufficient mathematical knowledge, his treatment of it was very faulty. Laplace assumed, to begin with, a huge mass of hot gas in a state of rotation. This assumption is not perfectly gratuitous, for the existence of such bodies is suggested by telescopic observation. As this mass of gas cooled it would contract and rotate faster. It would also assume a flattened form. There would come a stage in this process when the outermost ring of this flattened body would become detached from the main mass. This would happen when the centrifugal force of the outer rotating particles was just sufficient to balance the gravitational attraction drawing them towards the centre. The outermost ring, detached in this way, would, Laplace thought, condense and form a planet. The main mass would continue to contract and to increase its rate of rotation until a second ring was left behind, and then a third ring, and so on. Each of these would condense to form a planet. The remaining central mass is the sun. The planets, by rotating on their axes, would also throw off rings which, condensing in their turn, form satellites.
Although this theory enjoyed an immense popularity with scientific men for many years, modern mathematical research shows, pretty conclusively, that it cannot possibly be true. It appears that the scale is altogether too small. A rotating mass of gas, only large enough to supply the matter of the solar system, could not throw off planets. The rings that Laplace imagines being thrown off would not, as a matter of fact, condense. The mutual gravitational attraction of their particles would not be strong enough to prevail against the tendency of these particles to fly apart. Such rings of gas would merely dissipate themselves through space. They could not condense unless the primitive nebula was millions of times bigger than the nebula imagined by Laplace.
There is evidence for the existence of such nebula. They are the "spiral nebula," of which many millions are known to exist. Photographs of these bodies show them in all stages of development, and we see that they are passing through a process very like that imagined by Laplace. The process is not exactly the same for, instead of throwing off circular rings, these great nebulæ throw out spiral arms. Along the spiral arms there occur points of condensation. But each of these points results, not in a body the size of a planet, but in a body the size of a star. Laplace's nebular hypothesis, if applied on a scale sufficiently large to make it mathematically possible, results, not in the birth of planets, but in the birth of stars. As a theory of the birth of stellar universes it is pretty generally accepted. The change in the scale of the original theory is, we see, gigantic. A spiral nebula contains, on the average, enough material to make several thousand million stars. For such bodies Laplace's theory is applicable. It does nothing to explain the origin of the solar system.
The theory which seems to be, on the whole, the best attested supposes that the solar system resulted from a very rare accident. It is supposed that the planets were torn out of the sun by the close approach of a passing star. If the star were sufficiently massive and its approach sufficiently close, huge tides would be raised on the sun, and ultimately a colossal cigar-shaped filament would be torn out of it. Centres of condensation would be set up in this filament, and each of these centres would separate off as a planet.
The evidence for this theory is quite good. In the first place the cigar-shaped filament, thickest in the middle, corresponds pretty well with observed sizes of the planets. For, if we imagine the planets lying in a straight line from the sun, in the order of their distances, the largest planets, Jupiter and Saturn, occur about the middle of this line. In either direction from the middle, towards or away from the sun, the planets tail off in size—approximately, at any rate. They would fit fairly well into a cigar-shaped filament. At first the orbits of the planets would be very elliptical, not nearly circular, as they are now. And in the course of describing these elongated ellipses they would, at some period, pass very close to the sun. If they were still in a sufficiently plastic condition, the sun would act on them as the passing star had acted on the sun, and pull filaments out of them. These filaments would condense and so give rise to the satellites.
This theory may be pursued, quite convincingly, into details. Thus it is a curious fact that the two largest planets, Jupiter and Saturn, each have nine comparatively small satellites, while the earth and Neptune each have one comparatively large satellite. This may be explained by taking into account the different rates of cooling of these differently sized bodies. The mathematical theory shows that the more liquid a planet was at birth the less likely it would be to break up under the gravitational attraction of the sun. But, if it did break up, it would give birth to a comparatively large satellite. Now it is natural to suppose that the large planets, Jupiter and Saturn, remained gaseous longer than Neptune or the earth, and therefore each produced several small planets instead of one large one. Still smaller planets, Venus and Mercury, have no satellites at all.
An apparent difficulty arises with the other two planets. Both Mars and Uranus are something of a misfit in the cigar, being smaller than they should be. And they each have small satellites, Uranus having four, and Mars two. But this may be explained by supposing that they were the smallest planets to be born in the gaseous state, that their condensing power was therefore less, and that they therefore lost some of their material by dissipation. Thus the theory hangs, together very well, without any undue straining of the interpretation.
The theory also explains the fact that the planetary orbits are now nearly circular. At the beginning, as we have seen, they were very far from circular. But we may suppose that, in the catastrophic break-up of the sun. a great deal of dusty, gaseous matter would be scattered throughout the surrounding space. The planets in moving through this, dust, would be moving through a resisting medium, and it can be shown that the effect of this would be to make their orbits gradually approach the circular form. Indeed, the present departure of the planetary orbits from the strictly circular form enables the time that has elapsed since the break-up of the sun to be approximately calculated. The calculation is very approximate, however, owing to our lack of knowledge of the distribution of the primitive dust, and only allows us to say that the breakup occurred some time between one thou¬sand million and ten thousand million years ago. Much-closer limits can be reached by other methods, as we shall see later.
2
A probable figure for the age of the earth, in round numbers, is two thousand million years. For practically the whole of that time the earth has been mainly solid. It has been calculated that the earth must have solidified within fifteen thousand years of its birth. This is a very small fraction of its life. And ever since the solidification occurred, the temperature of the surface of the earth has remained practically the same as it is now. For it can be shown that heat from the interior could percolate only very slowly through the crust. By far the greater part of the heat came from the sun, and the sun's radiating power must have been very much the same then as it is now.
At first the solid rocks composing the crust would, of course, have been only a little below their boiling point, since they had only just cooled down enough to solidify. As they continued to cool they would contract violently, and enor¬mous fractures would occur. Having reached their present temperature, the rocks, as we have seen, would not get any cooler. But the inside of the earth would go on cooling and contracting until finally the outer crust would be left suspended, like a huge arch, without any material to rest on. There would come a time when the crust could no longer stand the strain, and it would collapse. Having settled down in its new position, the process would begin again, and after a time the crust would again collapse. It is thought that six or seven of these great crumblings can be traced in the earth's history. In this way, it is claimed, the existence of mountains on the earth's surface can be accounted for. There are other theories of mountain formation, but none, perhaps, so satisfactory as this.
But although this theory can account for the existence of mountains, it cannot account so satisfactorily for some other features of the earth's surface. In particular, it does not account for the distribution of earth and water. The great difficulty is the Pacific Ocean, which covers half the earth's surface. Why should all the land be crowded into one hemisphere of the earth? One theory suggests that the Pacific Ocean covers the depression left in the earth when the moon was torn out of it. But this supposes that the earth had solidified at the time the moon was born, and mathematical calculation seems to show that the moon could not have been born from a solid earth. The disruptive force of the gaseous sun would not have been sufficient, however close to it the earth may have passed. If, on the other hand, we suppose the earth to have been liquid, then obviously the separation of the moon from it could not have caused a depression, since the fluid would at once fill it up.
Another theory suggests that the great depression of the Pacific Ocean may have been scooped out by the primitive tides. We must remember that the moon only gradually moved away to its present distance from the earth. Now the nearer the moon is to the earth the greater is its tide-raising capacity. It can be calculated that, in those early days, the moon was raising tides nearly three miles high. Supposing that there already existed some difference of level between the northern and the southern hemisphere, these tides would tend to increase that difference. For water flows with more rapidity in an already deep place, and so tends to deepen it further. But this theory, like some others that have been proposed, is not much more, at present, than a speculation.
The age of the earth, since it solidified, can be determined with fair accuracy by a number of different methods. The best method is a result of the discovery of the radio-active elements. Uranium is such an element. It gradually transforms itself, at a perfectly definite rate, into lead. The rate of this transformation, it is found, is not altered by any extremes of temperature or pressure to which we can subject it. We are justified in regarding this rate as invariable. Fragments of uranium are found in certain rocks, and have doubtless formed part of those rocks since they first solidified. Together with the uranium we find lead. Now we cannot at once conclude, of course, that all the lead we find in the presence of uranium has been produced by the disintegration of uranium. But it so happens that lead produced from uranium is somewhat lighter than ordinary lead. It is possible to say, therefore, of any piece of lead, whether or not it has been produced by uranium disintegration. From this we can calculate how long the uranium present in that rock has been disintegrating, and since the uranium has been present in the rock ever since the rock solidified, we learn the age of the solid rock. Estimates of this kind tell us that the rocks cannot have solidified less than fourteen hundred million years ago. These estimates are based upon the contents of the oldest rocks known to us. It may be, therefore, that the earth is still older than this. Other considerations, however, make it unlikely that the earth could have been, say, twice or three times as old as this. A good round figure for its age, as we have already said, is two thousand million years. This figure also agrees very well with geological estimates.
3
The subsequent history of our earth is the chief concern of geology. It is strange that the science of geology is of such recent growth. The existence of various kinds of material — chalk, limestone, clay, etc. — arranged in layers one on top of the other, would have suggested, one thinks, that the top layers were formed after the lower ones. But it is usually supposed that this reflection was left for William Smith to make, an English surveyor, who roamed about England at the end of the eighteenth century, constructing canals. It had, however, occurred to people before him, and James Hutton had already published his ‘Theory of the Earth,’ in which he ascribes the different layers to a quiet orderly de¬posit over a long period, and not as due to one single catastrophic flood — the Deluge. But William Smith was the first to publish a coloured geological map and to discuss, in a satisfactory way, the distribution of fossils through the various geological layers.
The existence of fossils had long been known. We know now that fossils are the actual remains of animals or plants that have been buried by natural causes (even the cast of a fossil shell, that is, the impression it has left on the rock, is called a fossil), but for a long time they were supposed to be curious "sports" of nature. The fossil of a marine organism, for instance, found high up on a hill was, with the early notions of the creation of the world, a difficult thing to interpret. In the early part of the sixteenth century fossils were supposed by some Italians to have been formed in the hills by the action of the stars, a view which, prior to 1579, Leonardo da Vinci combated. Then the hypothesis arose of a plastic force or, according to Andrea Mattioli, a fatty matter capable of fashioning stones into organic forms. But the hypothesis which held its place longer than any other, and is not yet extinct among the unscientific, is that they were relics of the Mosaic deluge.
But William Smith showed that certain geological layers have each their characteristic series of fossils. Some of these fossils are like species now living. Others are perceptibly different. Smith showed that some members of a series are wont to occur also in the layer above, others in the layer below, others in all three. This persistence shows that changes in these particular animals and plants, at any rate, could not have been sudden. Smith also noticed that, the farther back we go, the more do the fossils differ from forms now living, until presently we come to layers where all the species are extinct, and differ markedly from anything living now.
Going still farther back we meet still other extinct forms, so that by the time we reach the lowest layers many dozens of extinct animals and plants have been encountered, all merging gradually into those above and below. Deeper still we find the fossils becoming exceedingly rare, and finally we reach a depth where they seem to be entirely absent.
These facts, in themselves, very strongly suggest a progress in time, and the early geologists, Button and Lyell, showed that small physical changes, operating through long periods of time, could account for the formation of the different geological layers. In Dr. Watts's words:
"Their work showed that physical processes, similar to those which, can be studied in operation in different parts of the world of the present, are sufficient to account for the nature of the rocks of the past and the phenomena presented by them; that rocks of all kinds are being worn down at slow but reasonable rates by rain, rivers, and the sea; that the debris is being transported and laid down layer by layer in lakes or on the sea-bed; that this sediment is being compacted into stony rock, lifted to form new land, deformed to produce the structures presented by the rocks themselves and by their aggregates in moun¬tain systems, sculptured and given the relief of land surfaces, cut down or depressed beneath the sea to receive a new load of sediment; that continents, too, may have been built and mountain ranges erected without any violent catastrophe, comparable in any degree with the magnitude of the earth as a whole, but as the outcome of slow and continually renewed movements, each on a comparatively small scale; and that all this has proceeded without any disturbing effect on, life, such as was contemplated by the catastrophists, though it must necessarily have had its influence on the details for its migration: that, in brief, the rocks which bear the record of the history of the earth are the product of an infinity of small causes operating through a vast range of time."
On the assumption that the geological layers have been gradually formed by processes such as are operating at the present day, it is possible to estimate, approximately, the time that has elapsed since the first rocks began to be formed. The maximum observed thicknesses of the various geological layers total 529,000 feet, a little over one hundred miles. The rates of deposition observed at the present day vary considerably according to the local conditions. Thus the rate for Great Britain may be taken as one foot in three thousand years, while for North America the rate is nearly three times as slow. On the other hand Egyptian deposits occur at the rapid rate of one foot every four or five hundred years. If we wish to get the same round figure of two thousand million years for the age of the earth that other methods have given us, we must assume that the geological layers have been deposited, on the average, at the rate of one foot per four thousand years. As we see by-looking at the present figures for Great Britain and North America, this is not at all an unreasonable figure. Thus we may say that the age of the earth, obtained from purely geological considerations, is fully consonant with the esti¬mates derived from entirely different sources and is, to that extent, a confirmation of the theories of the geologists.
We see that the geological evidence is that the earth's crust has, in the main, been formed in an orderly manner, and not by a succession of catastrophes. We have the same impression when we study the fossils contained in these layers. We have abundant evidence of a slow and orderly progression of animal and plant forms. The highest animals, for instance, the mammals, exist only in the newer rocks. Lower down we find reptiles and birds. Preceding these are amphibians, and preceding the amphibians are fishes. Beneath the fishes lies a vast thickness of rock containing only invertebrate animals. A similar progress is observed in the case of plants. There can be no question but that the more complex animals appeared on the earth later than the simpler ones, and it suggests itself that a process of ‘evolution’ has been at work, whereby the simpler creatures have grad¬ually given rise to the more complex. A detailed study of the geological records ought to show us all the steps of this process, and acquaint us with all the forms that living things have assumed.
But the difficulties attending the detailed examination are considerable. A large proportion of organisms will not be buried in conditions favourable for their preservation. Many of the bodies washed out to sea, for example, will be devoured by other creatures, and only their hard coverings would be likely to be preserved. Even when these are preserved, the influence of percolating water may dissolve them, or they may be destroyed by chemical and mechanical changes in the rocks themselves. Furthermore, layers which once formed part of the sea-bed may be raised above sea-level, and then the exposed portion is exposed to all the crumbling effects of weathering, so that it and its fossil contents are gradually dispersed. We must remember, also, that only a fraction of the earth's surface is exposed to observation in cliffs and quarries, etc., and that many of these exposed portions occur in countries not yet adequately investigated. It is possible, also, that some of the exposed portions have not been quarried in a way favourable to the exhibition of their fossil contents and, even where the contents are exposed, they often pass in the first instance through unskilled hands, and so are mangled and distorted by the time they reach those who could have interpreted their evidence.
We see, therefore, that it would be unreasonable to expect geology to provide us with a perfectly clear and detailed account of the development of living forms. Nevertheless, considering the necessary imperfections of the geological record, the amount of evidence it offers is quite surprising. This evidence makes it practically impossible to believe that all the various species of animals and plants have been separate creations. We are forced to conclude that species have been modified in the course of time, that they are not fixed, and that, on the whole, progress has been from the more simple to the more complex.
The general outlook that alone seems consistent with the facts is admirably put by Darwin when he says:
"If we admit that the geological record is imperfect in an extreme degree, then such facts as the record gives, support the theory of descent with modification. New species have come on the stage slowly and at successive intervals; and the amount of change, after equal intervals of time, is widely different in different groups. The extinction of species and of whole groups of species reappear when the chain of ordinary generation has once been broken. The gradual diffusion of dominant forms, with the slow modification of their descendants, causes the forms of life, after long intervals of time, to appear as if they had changed simultaneously throughout the world. The fact of the fossil remains of each formation being in some degree intermediate in character between the fossils in the formations above and below, is simply explained by their intermediate position in the chain of descent. The grand fact that all extinct organic beings belong to the same system with recent beings, falling cither into the same or into intermediate groups, follows from the living and the extinct being the offspring of common parents."
We are forced to very much the same reflections when we study the ‘geographical’ distribution of animals and plants, as Darwin goes on to say:
"Looking to geographical distribution, if we admit that there has been during the long course of ages much migration from one part of the world to another, owing to former climatical and geographical changes and to many occasional and unknown means of dispersal, then we can understand, on the theory of descent with modification, most of the great leading facts in Distribution. We can see why there should be so striking a parallelism in the distribution of organic beings throughout space, and in their geological succession throughout time; for in both cases the beings have been connected by the bond of ordinary generation, and the means of modification have been the same. We see the full meaning of the wonderful fact, which must have struck every traveller, namely, that on the same continent, under heat and cold, on mountain and lowland, on deserts and marshes, most of the inhabitants within each great class are plainly related; for they will generally be descendants of the same progenitors and early colonists. On this same principle, although two areas may present the same physical conditions of life, we need feel no surprise at their inhabitants being widely different, if they had been for a long period completely separated from each other; for, as the relation of organism to organism is the most important of all relations, and as the two areas will have received colonists from some third source or from each other, at various periods and in different proportions, the course of modification in the two areas will inevitably be different."
The evidence scattered both through time and space leads us to believe that species are not fixed. It is interesting, in this connexion, to note that the definition of a species has always been a difficult matter. Authorities often disagree as to whether two given creatures belong to the same or to different species.
Lamarck, who was the first to make the question of the constancy of species a matter of general scientific discussion, believed that there is a "natural sequence" for living organisms, and that, if we knew all the species that exist and that ever have existed, we should be able to form them into a sort of long ladder or chain so that, starting at the beginning, we would arrive, by a series of almost imperceptible steps, at the end. Lamarck held that all our schemes of classification of animals into distinct species are artificial, and this conviction led him to the idea that species are essentially fluid. He pointed out that domesticated animals differ very markedly from their wild originals, and that man, by selective breeding from a common ancestor, has produced extraordinary variations, as, for instance, the greyhound, the spaniel, the bull-dog. Everybody would say, judging merely from their appearance, that these animals belonged to different species, yet they have a common ancestor. Changes just as remarkable, said Lamarck, are constantly taking place in nature.
4
Lamarck's theory of evolution, although at one time pretty generally discredited, has now been revived by a number of prominent biologists. According to Lamarck, changes in an animal occur through use and disuse. Organs which are specially exercised become specially developed. The need for this special exercise arises from the conditions in which the animal lives; thus a changing environment, by making different demands on an animal, changes the animal. The giraffe, for instance, has developed its long neck in periods of relative scarcity by endeavouring to browse on higher and higher branches of trees. On the other hand, organs that are never exercised tend to disappear altogether. The eyes of animals that have taken to living in the dark grow smaller and smaller, generation after generation, until the late descendants are born eyeless.
The great assumption made by this theory is that the effects of personal, individual effort are transmitted to the offspring of that individual. This is a doctrine that is very much in dispute among modern biologists. We shall refer to this controversy later. In the meantime we must describe the most famous of all biological theories, the theory which, whatever its present position may be, has, by the attention it has directed to the matter, caused the ‘fact’ of evolution to be accepted by all biologists. That theory is Darwin's theory of Natural Selection.
We must first mention an apparently unrelated historical fact. At the end of the eighteenth century political theories were common subjects of discussion. The American Declaration of Independence and the manifestoes of the French Revolution made such topics as the "Rights of Man," "Natural Justice," etc. matters of general interest. Many philosophers taught that the day of complete liberty and complete equality for all men was about to dawn. The Rev. T. R. Malthus, mathematician and economist, reflected that this state of affairs would lead to a vast over-population of the world. In such a world, population would rapidly outgrow the means of subsistence and therefore, he argued, checks on population would be necessary if misery and vice were to be avoided. He expressed these ideas in a book called Essay on Population. This essay was read, years later, by two biologists, Darwin and Wallace, and it started the same train of thought in each of them.
Let us start from some simple arithmetical facts. "The common thrush," Professor MacBride tells us, "begins to produce eggs when it is one year old, and its average length of life is about ten years. Every year a pair of thrushes will rear two broods, each consisting of about four nestlings. Starting from the offspring of a single pair we find that if ail survived and mated, at the end of the tenth year, that is, at the completion of the life cycle of the parents, they would have produced a population of 19½ million. These in another ten years would grow to nearly 200 million million, and at the end of thirty years to about 1200 million million million. There would not be room for more than the one hundred and fifty-thousandth part of such an army of thrushes on the entire surface of the earth even if all stood side by side touching each other." Since, in fact, thrushes take up a very small part of the earth's surface, although they have been breeding for much more than thirty years, it is obvious that only a very small proportion of those born can survive and reproduce their kind. Similar remarks apply to innumerable other species of animals. Herrings, for instance, if allowed to proliferate undisturbed, would speedily choke up all the seas of the world. Darwin and Wallace were, of course, familiar with these facts, and it occurred to them that here we have Malthus's over-population problem in an exaggerated form. Malthus advocated "checks" to keep the population down. It is obvious that nature must apply checks of the most stringent kind. Of what nature are these checks?
They are varied, but the main ones are obvious when we reflect that the organism, whether plant or animal, must obtain food and avoid enemies. The success of the organism in doing this will in some cases be due to luck. We know that some seed falls on good ground, and some on stony ground. A falling slate from a roof may knock out the brains of a Newton as well as those of a cinema star. But such accidents do nothing to ‘vary’ a species. The most they could do would be to exterminate it. But those individuals of a species which possessed some mental or physical advantages over their fellows, who were better adapted to the common environment, would, in the ordinary struggle for existence, and apart from sheer bad luck, have a greater chance of surviving and reproducing their kind. And if these advan¬tages were of a kind that are inheritable, the species would tend to change.
That, briefly, is the simple idea of Natural Selection. Innumerable instances can be given. Thus it has often been recorded that lions, in attacking a herd of zebra or antelopes, invariably choose the weaker quarry. In general, as we should expect, strength and fleetness are advantages in the struggle for existence. This is so evidently what we would expect that it is hardly necessary to give instances of it. And we can easily see that there are many other characteristics, a greater or lesser measure of which would give their possessors a better chance of surviving.
The theory of natural selection thus rests upon two main facts, (1) that there are individual differences between members of the same species, and (2) that there is a struggle for existence. Each of these facts is incontrovertible. Offspring and parents are never exactly alike, a fact which makes selective breeding possible. And it is astonishing the varieties that selective breeding can produce, if continued over a long time, from small and haphazard differences. The amazingly various pigeons, for example, the pouter, the tumbler, and so on, are all descended from the ordinary rock pigeon. These varieties have been deliberately brought about by the breeder, who selects the points for which he will breed. He carefully mates those pigeons which have a vari¬ation in the required direction. The theory of natural selection states that a similar process occurs in nature. The struggle for existence takes the place of the human breeder. Nature sets a premium upon certain varieties as compared with others. Variations are continually occurring in all directions, as it were, and at random. Nature weeds out those that are unfavourable, and thus, little by little, a particular variation is established. It is supposed that in this way, given the vast periods of geologic time, every living and extinct species of animal and plant has been produced from some primitive form.
In this theory the origin of variations is left an unsolved problem. The theory merely states that they occur; it gives no reason for their occurrence. Further, Darwin, at any rate, assumed that the variations are always small, of the kind that we observe in daily experience. He also assumed that many of these variations occur entirely at random. But he also supposed that some of them come about through the purposive striving of the animal. He accepted, at any rate as a subsidiary factor, Lamarck's theory that the effects of use and disuse of organs can produce modifications which are inheritable.
The modern theory, what is called Neo-Darwinism, has been purified of certain of these assumptions. The notion that the effects of use and disuse can be inherited was at¬tacked by Weismann. He pointed out that the reproductive cell of an organism is derived solely from the reproductive cell of its parent. None of its characteristics depend upon the rest of the parent's body. The germ-plasm, as he called the substance of the reproductive cell, passes without breach of continuity from generation to generation. The various bodies which contain it, in its passage down the ages, are mere vehicles or sheaths for it. Nothing that happens to any particular body in this chain is transmitted to any subsequent body, unless the happening is of such a kind as to influence the germ-plasm. Weismann cut the tails off generation after generation of mice, but the subsequent generations of mice were all born with tails, and the tails showed no tendency to get shorter. It appears that the cutting-off of a tail does not influence the germ-plasm. Mutilations, at any rate, are not inheritable. That section of the human race that practices circumcision finds that the practice must be continued in every generation. There is no tendency for the effect to become inheritable.
More recent experiments have avoided the method of mutilation, and have studied the effect upon the organism of varying the environment in such ways as may be expected to occur in nature. Changes in the organism can be brought about in this way, but it is still a matter of controversy as to whether such changes are inheritable. The reader who is con¬cerned to accept only the definitely established conclusions of science roust regard the question of the inheritance of acquired characteristics as being still open.
It may be pointed out, incidentally, that Neo-Darwinism, by denying that the purposive striving of the organism has any influence on its evolution, makes the whole of evolution a mindless process. That is, so far as the mind incorporated in living organisms is concerned. It is still possible to hold, of course, that a Mind, a Designer, is controlling the course of evolution, but the means employed seem to be purely mechanical. Inheritable variations occur quite independently of any purpose or striving on the part of the organism. It is in this sense that variations are said to occur "at random." It may be, nevertheless, that a detailed study of the way variations come about will reveal "purpose," although this purpose is not expressible in terms of the personal ambitions of the organism.
The mechanism of heredity, about which a good deal is now known, was first illuminated by the researches of the Abbe Mendel. These researches were neglected for about half a century and were then encountered, almost simultaneously, by three independent biologists. To the student accustomed to the atmosphere of the "exact" sciences these researches, and the developments that have grown out of them, are quite unusually congenial. We here move in the clear and pleasant atmosphere of precise quantitative results and we have, underlying them, a theory at least as clear as the atomic theory in its early stages and one which, besides accounting for the known facts, leads to successful prediction. So much of biology, or at least of "natural history," presents us with an array of facts rather than gratifies our desire for comprehension. This is due, of course, to the sheer complexity of the subject and to the difficulty of isolating appropriate leading concepts. But in the matter of heredity, good working concepts have been found. They give no 'ultimate’ explanation, of course, any more than the atomic theory gave an ultimate explanation of the constitution of matter. And, in fact, the Mendelian theory is not unlike the atomic theory. The Mendelian theory asserts that inheritable characteristics are transmitted by discrete units. These units, from two parents, may exist side by side in the offspring, but they do not blend. We see at once that the laws of transmittance must be entirely different from what would occur in true blendings.
Let us consider, for example, a flower which exists in two varieties, red and white. The result of crossing these two varieties is to produce a pink flower. If these pink flowers are now bred between themselves, they do not produce, exclusively, pink flowers. They produce pink flowers, white flowers, and red flowers. We get the clue to the mechanism by which this occurs by studying the proportions in which these various colours are produced. In any large number we shall find that half the flowers are pink, a quarter red, and a quarter white.
The mechanism that would produce these results is very simple. Let us suppose, for example, that each flower, whatever its colour, contains two units of some kind which deter¬mines its colour. When two flowers are bred together, the offspring selects one unit from each parent. White flowers have two white-producing units. Red flowers have two red-producing units. When a white and a red flower are crossed, the offspring, which must take one unit from each parent, necessarily contains one red and one white unit. It is therefore a pink flower, and the crossing of a white and a red flower obviously can produce nothing but a pink flower. But now consider the result of breeding two pink flowers. Each flower contains a red and a white unit. The offspring may select a white from one and a white from the other. It will then be a white flower. Or it is just as likely to select a red from one and a red from the other. It will then be a red flower. Since each of these cases is equally likely we should expect to find as many white offspring as red offspring. But offspring containing one red and one white unit will occur just twice as often as either of the preceding cases. For the chance of selecting red-red is the same as the chance of selecting red-white. There will thus be a pink corresponding to every red. And the chance of selecting white-white is the same as the chance of selecting white-red. Thus there will be as many pinks as whites, for both red-white and white-red give pink. So we see that there will be twice as many pinks as there are either reds or whites. That is to say, one-half the progeny will be pink, and the other half will be split up equally into reds and whites. This agrees with the experimental evidence.
We see that these laws of inheritance are very different from those of pure blending. If, for instance, we cross a pink with a red we should expect, on the theory of pure blending, that the offspring would be a darker shade of pink. But on the present theory we see that each offspring must be like one or other of the parents, either an ordinary red or an ordinary pink. For the two units selected by the offspring must be either red-red or red-white. No other combination is possible. Similarly, the result of a cross between a pink and a white must be either a white or a pink.
The units we have discussed hitherto are supposed to be of equal strength, as it were. A red unit and a white unit are equally matched, with the result that, when they are both present, the product is pink. But there are many observed results that cannot be explained by this simple hypothesis. We have to introduce units which are ‘dominan’t and units which are ‘recessive.’ An organism which contains a dominant unit and a recessive unit will not manifest intermediate characteristics. It will only manifest the characteristics belonging to the dominant unit. If, in our previous example, red had been dominant and white recessive, then the results of a cross would all have been red. Each of the offspring would contain one red and one white unit, but in each case the white would have been overpowered, as it were, by the red. But if we breed from this new generation of reds, we shall get both reds and whites as offspring. For since each parent contains a red and a white unit the offspring may select a white unit from each parent. The offspring will then, of course, be white. All the other offspring will be red, but some of them will be true reds, that is reel-red, while the others will have the same units as our previous pinks, that is, red-white.
It was by studying the effects of units of this kind that Mendel was led to his theory. He experimented with two varieties of peas, Tall and Dwarf. "Tall" is a characteristic which is dominant to Dwarf. The result of the cross was to produce Tall peas, but these, when bred together, produced Dwarfs as well as Tails. And of the Talls produced, some turned out to be true Talls and the others hybrid Talls.
We see that a recessive unit is a sort of lurking character¬istic. Only when combined with another recessive unit can it manifest itself. It is stated, for instance, that, in the eyes of human beings, brown is dominant to blue. Thus a brown-eyed couple may give birth to a blue-eyed child. For it may be that neither parent is truly brown; each of them may be brown-blue. So that the child may select the blue unit from each parent. But it is evident that blue-eyed parents cannot give birth to a brown-eyed child. For blue eyes cannot exist unless they are blue-blue, unless they are blue all through, as it were. Thus there can be no brown units for the child to select. According to some authorities there are certain human abnormalities, some kinds of insanity and deaf-mutism, which are produced by recessive units. Thus it can happen that two normal people can produce an idiot child.
So far we have, in any particular case, dealt with only one characteristic, colour, height, and so on. But any organism has, of course, many characteristics. Each of these characteristics obeys Mendel's laws, and they are inherited independently of one another. Thus the possible combinations that can result from crossing, when we take into account several characteristics, can be very numerous.
The physical basis of these laws has been discovered. It has long been known that every living thing is built up out of "cells," and each cell contains a number of microscopic bodies called chromosomes. The cells of each species of organism contain their own distinctive set of chromosomes. A cell of the human body, for example, contains forty-eight chromosomes. For some creatures there are only two chromosomes, for others some hundreds. And chromosomes differ in size and shape.
Cells grow by division. A cell splits in half and becomes two cells. This process is accompanied by a number of very complicated internal phenomena, but the upshot of it, from our present point of view, is that each daughter cell emerges with the same chromosome outfit that was possessed by the original cell. This is secured by the fact that each chromosome, while the original cell is dividing, splits in half along its length, one half going to one daughter cell and other half to the other. An exception occurs when the reproductive cells are being made. In that case the chromosomes of the original cell do not split in half, but half the total number goes to one daughter cell and half to the other. Thus the human ovum and the human spermatozoon each contains twenty-four chromosomes. When the ovum is fertilized, the spermatozoon adds to its own stock of chromosomes, and thus the fertilized cell contains its proper outfit of forty-eight chromosomes, half being derived from the female and half from the male. This is the mechanism of heredity.
In speaking of the "mechanism" of heredity we are using a term that is commonly employed by biologists. One must not conclude, however, that any mechanical explanation of these phenomena has been given. As a matter of fact, a mechanical explanation has not been even remotely approached, and some biologists believe that such an explanation is impossible. These biologists maintain that the sciences of life must use concepts peculiar to themselves, and that the concepts found adequate for physics and chemistry are inadequate for the phenomena of life. There has always, of course, been a school of biologists who hold that life cannot be explained on mechanical principles. Amongst them we must reckon the vitalists who asserted that a vital force, besides the forces known to physics and chemistry, plays a part in living phenomena. Vitalism is now discredited, how¬ever, but it does not follow that mechanics will be found sufficient. It is the less likely in view of the fact that mechanics has been found insufficient even in physics itself. A really adequate group of concepts, applicable to biological phenomena, has not yet been isolated.
Chromosomes are not simple bodies. Each chromosome is supposed to contain a chain of still smaller bodies, called genes, and these genes are the real units of heredity. Experiments, in particular the famous series of experiments carried out by Professor Morgan and his school on the fruit-fly ‘Drosophila melanogaster,’ seem to make it clear that each gene is responsible for a definite characteristic. On the evidence afforded by a prolonged series of experiments Professor Morgan has constructed a map showing the distribution of the genes in the chromosomes of the fruit-fly, and against each gene is the particular characteristic for which it is responsible. Colour, shape of wing, presence or absence of eyes, and various other characteristics have been mapped in this way. In some cases a single gene is sufficient to produce a very marked effect. In other cases the effect is produced by a number of genes conspiring together. It can happen, also, that different genes counteract one another. It cannot yet be definitely asserted that all inheritance depends on genes. But the possible exceptions are comparatively few, and it seems clear that in nearly all cases the genes play at least the predominant role.
If we suppose that all inheritable characteristics are conveyed by the genes, we see that the theory of evolution requires us to suppose that changes in the genes can occur. The various theories of evolution, therefore, are really theories as to how these changes take place. There is no doubt, to begin with, that changes do occur. Sudden alterations, in both animals and plants, have often been observed. These alterations are not mere variations, such as are produced by the ordinary shuffling of the genes; they are much more radical and testify to an actual change in the germ-plasm itself. They are called ‘mutations.’ A number of biologists, perhaps the majority, believe that mutations occur at random. Others believe that individual striving, on the part of the animal, can affect its germ-plasm, or that environmental influences can produce changes in it.
There is also the theory called Orthogenesis which slates that the germ-plasm, in particular cases, at any rate, is predetermined to develop in certain ways. This development goes on quite irrespective of whether or not it is advantageous to the organism concerned. And there are the vitalistic theories, of which Bergson's ‘Elan Vital’ is the most celebrated. We here have the course of evolution attributed to a purposeful striving manifesting itself in matter. This purposeful striving is not the God of the old theologians. It is not something directing the evolutionary process from outside, it is something embodied and manifested in the world of living things, and in ourselves it has reached consciousness. None of these theories has yet received general assent and, in this sense, the contribution of biology to modern thought is not yet unambiguous. So far as biology is concerned, Plato's summary of the Greek theory that everything came about by "chance" is still a possible, but not a necessary, belief.
The theory of genes and mutations makes the process of inheritance much more intelligible than it was before. It is not yet generally agreed, however, that in mutations we have found the actual raw material with which evolution has worked. Observed mutations, say some authorities, are not sufficiently profound to explain the origin of species. And it has been asserted that, of the mutations that have actually been produced under experimental conditions, practically all are detrimental to the organism concerned. In spite of the immense number of observations that have been made, and of the detailed experimental work that has been clone in recent years, there is not yet unanimity of opinion as to the way, or ways, in which evolution has come about.
But as to the fact of evolution there is universal assent. A study of the world of living things, present and past, makes such a conclusion inevitable. On a broad sweep, the progress from simple to more complicated forms is too obvious to be disputed. There are instances, it is true, where nature seems to go backwards. It has happened that evolution seems to reach its limit in some particular direction, and that the end-products of the process become extinct, while some still surviving ancestral simple form starts off evolving on a new line. Such eddies in the main current are not always explainable, but, in general, the emergence of the different species of animals and plants in time fits in with the evolutionary hypothesis.
The beginning of the evolutionary process raises a question which is as yet unanswerable. What was the origin of life on this planet? Until fairly recent times there was a pretty general belief in the occurrence of "spontaneous generation." It was supposed that lowly forms of life developed spontaneously from, for example, putrefying meat. But careful experiments, notably those of Pasteur, showed that this conclusion was due to imperfect observation, and it became an accepted doctrine that life never arises except from life. So far as actual evidence goes, this is still the only possible conclusion. But since it is a conclusion that seems to lead back to some supernatural creative act, it is a conclusion that scientific men find very difficult of acceptance. It carries with it what are felt to be, in the present mental climate, undesirable philosophic implications, and it is opposed to the scientific desire for continuity. It introduces an unaccountable break in the chain of causation, and therefore cannot be admitted as part of science unless it is quite impossible to reject it. For that reason most scientific men prefer to believe that life arose, in some way not yet understood, from inorganic matter in accordance with the laws of physics and chemistry.
There is also the hypothesis, held by a few distinguished scientific men, that life is as old as matter and, in that sense, has had no origin. Lord Kelvin thought that the germs of life may have reached our planet from some other world. We are to picture these "germs" wandering about space from the beginning of time, and developing into various forms of living things whenever they strike a favourable soil. This means, of course, that the life of the wandering germs can remain dormant for an indefinite time. Arrhenius maintained that this was possible owing to the low temperature and lack of water-vapour in interstellar space. It has been found that certain bacteria, kept at a temperature of —200° C., are still alive at the end of six months, and the seeds of certain plants have been found to be still alive at the end of a century. Loeb stated that there is no reason why spores should lose more of their germinating power in ten thousand years than in six months. But, naturally, the indefinite persistence of life in the conditions of interstellar space is not a matter that can be tested experimentally. If it is to be believed, it must be as an article of faith.
The hypothesis that life has developed from inorganic matter is, at present, still an article of faith, although various chemists have put forward various hypothetical accounts as to how they think it might have been clone. The fact remains, however, that none of these processes have been reproduced in a laboratory, and so their possibility lacks experimental proof. This aspect of the question was best summed up by T. H. Huxley sixty years ago. Modern knowledge has nothing essential to add:
"Looking back through the prodigious vista of the past, I find no record of the commencement of life, and therefore I am devoid of any means of forming a definite conclusion as to the conditions 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 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 protoplasm from not living 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 protoplasm from such matters as ammonium carbonates, oxalates and tartrates, alkaline and earthly 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."
It may be that some light will be thrown upon the general question by the further investigation of what are called the "filter-passing" organisms. These organisms are too small to be seen by the microscope, and they reveal their presence only indirectly. They are the cause of certain diseases. The question has been raised as to whether they are "alive" or not, and it seems that the question can be answered both ways. In fact, their characteristics reveal an unsuspected ambiguity of the term "life." It is possible that we have here a connecting link between what we ordinarily mean by living and not living matter.
In surveying this account of the way in which the world came to be as it is, we see that none of the chief hypotheses belong to the very highest class of scientific theory. None of them have the degree of validity of, for example, the electromagnetic theory of light. And it is unlikely that they ever will have this degree of validity, since they cannot be subjected to the test of experiment. The theory that the planets were born from the sun by the tidal effects of a passing star is such a theory. Even if instrumental power were so developed as to make such a phenomenon observable in some distant part of the heavens, the chances against its occurrence are so great as to make it very unlikely that it would ever be observed. Theories as to the early history of our planet are in a similar case; they deal with a set of conditions that cannot be reproduced. In this sense they may be called historical theories and, like history itself, they may reach a high degree of validity.
Theories of evolution do not altogether belong to this class. Evolution is presumably still going on, and is presumably due to the same causes that operated in past times. By selecting organisms which have a short life and which breed rapidly, such as ‘Drosophila,’ and perhaps by speeding up the process by artificial restrictions, it may be that we shall actually observe the process of evolution. Observation of the geological records suffices to establish the fact that evolution has occurred; the definite determination of the method of its occurrence must presumably await the results of experimental investigation.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< Whew!
"It is in its aesthetic aspect," he says, "that the chief charm of science resides."
Maybe we can explore this facet of Sullivan's Mind at a later date. JEO
NOTE: permission to reprint portions of "Limitations of Science" has not as yet been obtained from the Viking Press Inc.
posted by James E. Opfell @ 8:11 PM
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