Alfred Russel Wallace

“ The world-wide distribution of atmospheric dust is a remarkable phenomenon. As the blue colour of the sky is universal, the whole of the higher atmosphere must be pervaded by myriads of ultra-microscopical particles, which, by reflecting the blue rays only, give us not only the azure vault of heaven, but in combination [ 256] with the coarser dust of lower altitudes, diffused daylight, the grand forms and motions of the fleecy clouds, and the 'gentle rain from heaven' to refresh the parched earth and make it beautiful with foliage and flowers. ”

“ Lastly, I submit that the whole of the evidence I have here brought together leads to the conclusion that our earth is almost certainly the only inhabited planet in our solar system; and, further, that there is no inconceivability—no improbability even—in the conception that, in order to produce a world that should be precisely adapted in every detail for the orderly development of organic life culminating in man, such a vast and complex universe as that which we know exists around us, may have been absolutely required. ”

“ It has been the consideration of our wonderful atmosphere in its various relations to human life, and to all life, which has compelled me to this cry for the children and for outraged humanity. Will no body of humane men and women band themselves together, and take no rest till this crying evil is abolished, and with it nine-tenths of all the other evils that now afflict us? ”

“ Of beetles alone there are at least a hundred thousand distinct species now living, while in some parts of sub-arctic America mosquitoes are sometimes so excessively abundant that they obscure the sun. And when we think of the myriads that have existed through the vast ages [ 321] of geological time, the mind reels under the immensity of, to us, apparently useless life.
All nature tells us the same strange, mysterious story, of the exuberance of life, of endless variety, of unimaginable quantity. All this life upon our earth has led up to and culminated in that of man. ”

“ They hold that the marvellous complexity of forces which appear to control matter, if not actually to constitute it, are and must be mind-products; and when they see life and mind apparently rising out of matter and giving to its myriad forms an added complexity and unfathomable mystery, they see in this development an additional proof of the supremacy of mind. Such persons would be inclined to the belief of the great eighteenth century scholar, Dr. Bentley, that the soul of one virtuous man is of greater worth and excellency than the sun and all his planets and all the stars in the heavens ”

“ All the motions and functions of living things are periodic; growth and repair, assimilation and waste, go on alternately. All our organs are subject to fatigue and require rest. All kinds of stimulus must be of short duration or injurious results follow. Hence the advantage of darkness, when the stimuli of light and heat are partially removed, and we welcome 'tired nature's sweet restorer, balmy sleep'—giving rest to all the senses and faculties of body and mind, and endowing us with renewed vigour for another period of activity and enjoyment of life. ”

“ We have already seen within what narrow limits the temperature on a planet's surface must be maintained in order to develop and support life. We have also seen how numerous and how delicate are the conditions, such as density of atmosphere, extent and permanence of oceans, and distribution of sea and land, which are requisite, even with us, in order to render possible the continuous preservation of a sufficiently uniform temperature. Slight alterations one way or another might render the earth almost uninhabitable, through its being liable to alternations of too great heat or excessive cold. ”

“ There is, therefore, very good reason for the belief that the adaptability of a planet for a full development of life is primarily dependent, within very narrow limits, on its size and, more directly, on its mass. But if the earth owes its specially constituted atmosphere and its nicely adjusted quantity of water to such general causes as here indicated, and the same causes apply to the other planets of the solar system, then the only planet on which life can be possible is Venus. ”

“ We thus see that light is not a simple and uniform radiation from the sun, but is made up of a large number of separate rays, each of which produces in our eyes the sensation of a distinct colour. Light is now explained as being due to vibrations of ether, that mysterious substance which not only permeates all matter, but which fills space at least as far as the remotest of the visible stars and nebulæ. The exceedingly minute waves or vibrations of the ether produce all the phenomena of heat, light, and colour, as well as those chemical actions to which photography owes its wonderful powers. ”

“ Proctor argues, that 'The vast supplies of heat thus emitted by the stars not only suggest the conclusion that there must be worlds around these orbs for which these heat-supplies are intended, but point to the existence of the various forms of force into which heat may be transmuted. We know that the sun's heat poured upon our earth is stored up in vegetable and animal forms of life; is present in all the phenomena of nature—in winds and clouds and rain, in thunder and lightning, storm and hail; and that even the works of man are performed by virtue of the solar heat-supplies. ”

“ It has been well said that what we commonly term the sun is really the bright spherical nucleus of a nebulous body. This nucleus consists of matter in the gaseous state, but so compressed as to resemble a liquid or even a viscous fluid. About forty of the elements have been detected in the sun by means of the dark lines in its spectrum, but it is almost certain that all the elements, in some form or other, exist there. This semi-liquid glowing surface is termed the photosphere, since from it are given out the light and heat which reach our earth. ”

“ We could have plants without animals; we could not have animals without plants. And all this marvel and mystery of vegetable life, a mystery which we rarely ponder over because its effects are so familiar, is usually held to be sufficiently explained by the statement that it is all due to the special properties of protoplasm. Well might Huxley say, that protoplasm is not only a substance but a structure or mechanism, a mechanism kept at work by solar heat and light, and capable of producing a thousand times more varied and [ 199] marvellous results than all the human mechanism ever invented. ”

“ The most eminent astronomers in every part of the world look forward to the solution of these problems not, perhaps, as of any great value in themselves, but as steps towards a more complete knowledge of our universe as a whole. Their aim is to do for the star-system what Darwin did for the organic world, to discover the processes of change that are at work in the heavens, and to learn how the mysterious nebulæ, the various types of stars, and the clusters and systems of stars are related to each other. ”

“ How infinite in faculty! In form and moving, how express and admirable! In action how like an angel! In apprehension how like a god!' And for the development of such a being what is a universe such as ours? However vast it may seem to our faculties, it is as a mere nothing in the ocean of the infinite. ”

“ We thus find that the vast, invisible ocean of air in which we live, and which is so important to us that deprivation of it for a few minutes is destructive of life, produces also many other beneficial effects of which we usually take little account, except at times when storm or tempest, or excessive heat or cold, remind us how delicate is the balance of conditions on which our comfort, and even our lives, depend. ”

“ If there are myriads of other worlds, it seems incredible that they should each be the object of a special revelation and a special sacrifice. If, on the other hand, we are the only intelligent beings that exist in the material universe, and are really the highest creative product of a Being of infinite wisdom and power, they cannot but wonder at the vast apparent disproportion between the Creator and the created, and are sometimes driven to Atheism from the hopelessness of comprehending so mean and petty a result as the sole outcome of infinite power. ”

“ Professor Simon Newcomb calculates that, if there are one hundred million stars in the stellar universe each five times the mass of our sun, and spread over a space which light would require thirty thousand years to cross, then any mass traversing such a system with a velocity of more than twenty-five miles a second, would fly off into infinite space never to return. Now as there are many stars which have, apparently, very much more than this velocity, it would follow that the visible universe is unstable. ”

“ Had the vast mass of matter postulated by Lord Kelvin acquired no motion of revolution, but have fallen continuously towards the centre of mass, the motions developed when the more distant bodies approached that centre would have been extremely rapid; while, as they must have fallen in from every direction, they would have become more and more densely aggregated, and collisions of the most catastrophic nature would frequently have occurred, and this would have rendered the central portion of the universe the least stable and the least fitted to develop life. ”

“ It is the method of measuring the rate of motion of any of the visible heavenly bodies in a direction either directly towards us, or directly away from us, technically described as 'radial motion,' or by the expression—'in the line of sight.' And the extraordinary thing is that this power of measurement is altogether independent of distance, so that the rate of motion in miles per second of the remotest of the fixed stars, if sufficiently bright to show a distinct spectrum, can be measured with as much certainty and accuracy as in the case of a much nearer star or a planet. ”

“ Where, in the very brightest portion of the Galaxy, will we find a part equal in angular magnitude to the moon which affords us the same quantity of light? In the very brightest spot, the light probably does not amount to one hundredth part that of the full moon.' It follows that, even if dark stars were fifteen million times as numerous as the bright ones, Professor Newcomb's argument would still apply against an infinite universe of stars of the same average density as the portion we see. ”

“ We have seen how great is the difference in the estimates of geologists and those of physicists as to the time that has elapsed during the whole development of life. But the position we have now found for the sun, in the outer portion of the central star-cluster, may afford a clue to this problem. What we require is, some mode of keeping up the sun's heat during the enormous geological periods in which we have evidence of a wonderful uniformity in the earth's temperature, and therefore in the sun's heat-emission. ”

“ We do not say that organic life could not exist under altogether diverse conditions from those which we know or can conceive, conditions which may prevail in other universes constructed quite differently from ours, where other substances replace the matter and ether of our universe, and where other laws prevail. But, within the universe we know, there is not the slightest reason to suppose organic life to be possible, except under the same general conditions and laws which prevail here. ”

“ The whole bearing of the geological evidence indicates the wonderful continuity of conditions favourable for life, and for the most part of climatal conditions more favourable than those now prevailing, since a larger extent of land towards the North Pole was available for an abundant vegetation, and in all probability for an equally abundant animal life. We know, too, that there was never any total break in life-development; no epoch of such lowering or raising of temperature as to destroy all life; no such general subsidence as to submerge the whole land-surface. ”

“ The Obliquity of the Ecliptic
The effect of the obliquity of the earth's equator to its path round the sun, upon which depend our varying seasons and the inequality of day and night throughout all the temperate zones, is very generally known. But it is not usually considered that this obliquity is of any great importance as regards the suitability of the earth for the development and maintenance of life; and it seems to have been passed over as an accident hardly worth notice, because almost any other obliquity or none at all would have been equally advantageous. ”

“ Taking first our earth, he shows that the period during which life has existed upon it is very small in comparison with that during which it must have been slowly forming and cooling, and its atmosphere condensing so as to form land and water on its surface. And if we consider the time the earth has been occupied by man, that is a very minute part, perhaps not the thousandth part, of the period during which it has existed as a planet. ”

“ But this problem of measuring the sun's distance, and through it the dimensions of the orbits of all the planets of our system, sinks into insignificance when compared with the enormous difficulties in the way of the determination of the distance of the stars. As a great many people, perhaps the majority of the readers of any popular scientific book, have little knowledge of mathematics and cannot realise what an angle of a minute or a second really means, a little explanation and illustration of these terms will not be out of place. ”

“ It appears certain, therefore, that with half our present bulk of atmosphere life would be hardly possible on the earth on account of lowered temperature alone. And as there would certainly be an added difficulty in the needful supply of oxygen to animals and carbonic acid to plants, it seems highly probable that a reduction of density of even one-fourth might be sufficient to render a large portion of the globe a snow and ice-clad waste, and the remainder liable to such extremes of climate that only low forms of life could have arisen and been permanently maintained. ”

“ Before the discovery of the telescope the sizes of the planets were quite unknown, while the most that could be ascertained about the stars was, that they were at a very great distance from us. This being the extent of the knowledge of the ancients as to the actual dimensions and constitution of the visible universe, of which, be it remembered, the earth was held to be the centre, we cannot be surprised at the almost universal belief that this universe existed solely for the earth and its inhabitants. ”

“ Before trying to comprehend the physical conditions on any planet which are essential for the development and maintenance of a varied and complex system of organic life comparable to that of our earth, we must obtain some knowledge of what life is, and of the fundamental nature and properties of the living organism.
Physiologists and philosophers have made many attempts to define 'life,' but in most cases in aiming at absolute generality they have been vague and uninstructive. ”

“ Not only, therefore, is a sun needed to give light and heat, but it is quite possible that any sun would not answer the purpose. A sun is required whose light possesses those special rays which are effective for this operation, and as we know that the stars differ greatly in their spectra, and therefore in the nature of their light, all might not be able to effect this great transformation, which is one of the very first steps in rendering animal life possible on our earth, and therefore probably on all earths. ”

“ We have here a complete scheme of evolution, carrying us from those ill-defined but enormously diffused masses of gas and cosmic dust we know as nebulæ, through planetary nebulæ, nebulous stars, variable and double-stars, to red and white stars and on to those exhibiting the most intense blue-white lustre. We must remember, however, that the most brilliant of these stars, showing a gaseous spectrum and forming the culminating point of the ascending series, are not necessarily hotter than, or even so hot as, some of those far down on the descending scale ”

“ And to those who urge that in other worlds there may be other laws of nature which may render them quite as habitable by intelligent beings as our world is for us, he replies, that if we are to suppose new laws of nature in order to render each planet habitable, there is an end of all rational inquiry on the subject, and we may maintain and believe that animals may live on the moon without air or water, and on the sun exposed to heat which vaporises earths and metals. ”

“ On the whole, then, we have positive knowledge of the existence, in the sun, stars, and planetary and stellar spaces, of such a large proportion of the elements of our globe, and so few indications of any not forming part of it, that we are justified in the statement, that the whole stellar universe is, broadly speaking, constructed of the same series of elementary substances as those we can study upon our earth, and of which the whole realm of nature, animal, vegetable, and mineral, is composed. ”

“ But it is no new thought, no modern discovery, that we are thus utterly powerless to conceive or comprehend the idea of an Infinite Being, Almighty, All-knowing, Omnipresent, and Eternal, of whose inscrutable purpose the material universe is the unexplained manifestation. Science is in presence of the old, old mystery ”

“ It is only when a planet attains a mass at least a quarter that of the earth that it is capable of retaining water-vapour, one of the most essential of the gases; but with so small a mass as this, its whole atmosphere would probably be so limited in amount and so rare at the planet's surface that it would be quite unable to fulfil the various purposes for which an atmosphere is required in order to support life. ”

“ Yet further, even among stars having a similar physical constitution to our sun and of an equal or greater mass, only a portion of their period of luminosity would be suitable for the support of planetary life. While they are in process of formation by accretions of solid or gaseous masses, they would be subject to such fluctuations of temperature, and to such catastrophic outbursts when any larger mass than usual was drawn towards them, that the whole of this period—perhaps by far the longest portion of their existence—must be left out of the account of planet-producing suns. ”

“ With infinite space around us and infinite time before and behind us, there is no incongruity in this conception. A universe as large as ours for the purpose of bringing into existence many myriads of living, intellectual, moral, and spiritual beings, with unlimited possibilities of life and happiness, is surely not more out of proportion than is the complex machinery, the life-long labour, the ingenuity and invention which we have bestowed upon the production of the humble, the trivial, pin. ”