The Fitness of the Environment

drogen and carbon must exist at or near the surface when a crust forms upon a cool- ing star. The nature of the chemical combinations into which these elements at first enter is perhaps open to some question. But as the temperature falls in the cooling of a sun or planet the affinities of carbon and hydrogen for oxygen increase, so that carbonic acid and water must normally result. For oxygen is almost certainly present in the sun; it is found in meteorites, and the vast store of it in the earth's atmosphere and crust (roughly one half of their total mass) justifies the be- lief that it is everywhere one of the commonest of elements. Hence an atmosphere contain- ing water and carbonic acid appears to be a normal envelope of a new crust upon a cooling body. Even were not these substances at first present in such an atmosphere, volcanoes must soon belch them forth in enormous quantities to relieve the pressure which inevi- table chemical processes set up.

It is clear that no one can give an exhaus- tive description of the formation of the earth's atmosphere and the changes which underlie vulcanism, so long as the theoretical considera- tions involved remain often more obscure than the facts. However, be the process what it may, it is at least automatic, and must repeat itself in other similar circumstances. There is, moreover, direct evidence in sup- port of the above conclusions. Spectro- scopic investigation has proved the presence of water vapor in the atmospheres of Mars, Venus, Jupiter, and Saturn, and nobody has suggested what the snowcaps of Mars may be unless they are real snow (hoarfrost) or, im- probably, carbonic acid. Lowell and Arrhe- nius agree in considering them snowcaps.^

In the earth's atmosphere carbonic acid has been very largely converted into oxygen and vegetable matter, which later has been turned into enormous quantities of coal. It is, in fact, possible, in accordance with the sugges- tion of Koene, that all the oxygen of the atmosphere has been thus formed from car- bon dioxide, and that therefore coal, peat, and other similar substances within the earth are chemically equivalent to the oxygen now free. If a typical atmosphere must contain water and carbon dioxide, its evolution must ob- viously be in part conditioned by the presence of these substances. Hence terrestrial meteor- ology, no less than terrestrial geology, must be in greater or less degree a special case of a

general process, and meteorological condi- tions on the earth cannot be perfectly unique. A number of circumstances, however, cause far greater variations in meteorological pro- cesses than in most other phenomena which have yet been discussed. For instance, on small astronomical bodies with weak gravi- tational attractions atmospheres cannot long endure. Like the moon these bodies must gradually lose nearly all their gases to space. Such loss has almost certainly occurred from the earth itself, and probably accounts for the absence of hydrogen and helium from the air. These gases, being very light, are not attracted with sufficient force to the earth, and gradually rise to the upper level of the atmosphere and fly away. Again, in the ab- sence of a near-by sun which steadily provides energy to balance loss by radiation, the period during which water and carbonic acid can remain in an atmosphere must be relatively short. Gradually, but in a time wholly in- considerable in comparison with the duration of the terrestrial atmosphere, the gases sur- rounding bodies so placed must condense and then solidify. Finally, a body which con- stantly turns one face to a sun must slowly condense its whole atmosphere upon its dark.

cold surface, and so no less certainly be de- prived of a gaseous envelope and of oceans. Accordingly it appears safe to say that really durable atmospheric conditions depend j upon sufficient size of the planet, the presence I of a sun, and rotation.^ No doubt a host of other factors which exist in the case of the earth are only less important. In any event, all such phenomena, though varied by chance, are of automatic origin, and whatever may be the peculiarities of our solar system there is no reason to suppose that like conditions are not of frequent occurrence. Throughout space there must be thousands of planets which, like the earth and Mars, are enveloped in an atmosphere that endures through count- less centuries, and that contains great quan- tities of water and carbon dioxide. ! All such atmospheres must in greater or less degree manifest general meteorological phenomena. There must be winds and clouds, rain and snow and ice, the formation of oceans and ocean currents, streams and lakes, all in- terrelated by complex cyclic processes which endure. Tides, too^ and magnetic and elec- trical phenomena cannot be absent, while

1 A full discussion of all such problems will be found in the "Lehrbuch" of Arrhenius and in S. GUnther's "Handbuch der Geophysik." Two volumes, Stuttgart. 1897-1898. the action of water through long ages must accomphsh its gigantic work of disintegration and sedimentation. Soil must be formed, and water must penetrate it. In short a possible abode of life not unlike the earth apparently must be a frequent occurrence in space. Such, in the present state of knowledge, are the general cosmographical views which naturally suggest themselves to one who considers the possibility of life throughout the universe. The solar system appears to be, in its most general traits, a fair sample of the whole ; the sun is a typical star ; the planets are certainly members of a large class of similar bodies. These various types of material aggregation are a good deal alike , wherever they occur. They are formed of the same matter, probably in very much the same proportions. They are actuated by the same manifestations of the same energy, and their evolutionary histories are similar. One and all are likely to possess, for a longer or shorter time, climates which make life possible. On the other hand, it is already obvious that

the solar system, and especially the earth among planets, are very favorable for life, partly through apparently accidental circum- stances. Putting aside, therefore, the biological fitness of the special climates of the earth both as a familiar fact, and as possibly in no small de- gree accidental, we may more advantageously give our attention at once to other phenomena which appear to be of a far more general character, — the occurrence of large quanti- ties of water and carbon dioxide in the atmos- phere, and the fundamental meteorological processes which their presence involves. Ni- trogen and various other substances auto- matically find a place beside water and car- bonic acid, but it will be convenient to pass them by or to postpone the consideration until other aspects of the subject have been more fully developed.

Of course a consideration of the prop- erties of water and carbonic acid might be approached from a study of terrestrial processes exclusively. But since the assump- tion that such phenomena are common occur- rences throughout the universe, and that they are the normal result of cosmic evolution, does not in any way modify the subsequent course of the inquiry, there appears to be no loss of logical security from its introduction. Mean- while the evidence that the special phenomena under discussion are probably the nowise ex- ceptional outcome of the operation of general laws, and not merely sporadic, cannot fail to lend weight to whatever conclusions may ultimately be reached.

Obviously it is in the physical and chemical attributes of these two compounds and their constituent elements that we find very many of the conditions which make life possible upon the earth. They are material, provided and mobilized automatically, out of which living things undoubtedly can be formed. Moreover if we limit our study to the physico- chemical properties of water and carbonic acid, and to the compounds of carbon, hydro- gen, and oxygen, we shall greatly simplify our problem. It cannot be denied that this re- striction, no less than the earlier decision to restrict the postulated characteristics of life to complexity, regulation, and metabolism, is sure to limit the inquiry, often perhaps in a very unwelcome manner. On the other hand, the gain in economy and security is once

more of great importance, and at present is perhaps essential to clear thinking. Such a procedure manifestly influences not at all the validity of any conclusions which may be reached; only it must not be forgotten that the conclusions apply directly to our limited field of inquiry alone. Such is the outcome of a preliminary glance at the many departments of science which are necessarily involved in the ques- tion of fitness of the environment. Living things permit themselves to be simplified into mechanisms which are complex, regulated, and provided with a metabolism ; the environ- ment, by a series of eliminations, is reduced to water and carbonic acid. These are sim- plifications counseled solely by expediency. Neither logical process is necessary ; each in- volves a disregard for many circumstances which might be of weight in the present in- quiry. But in the end there stands out a perfectly simple problem which is undoubt- edly soluble. That problem may be stated as follows : In what degree are the physical, \ chemical, and general meteorological char- !

acteristics of water and carbon dioxide and of the compounds of carbon, hydrogen, and oxygen favorable to a mechanism which must be physically, chemically, and physiologi- cally complex, which must be itself well regu- lated in a well-regulated environment, and which must carry on an active exchange of matter and energy with that environment ? The first step in seeking a solution must be to review the data of physics and chemistry which describe the properties of water and carbonic acid, having due regard to their meteorological significance. Such data of the highest accuracy exist in great profusion, for almost every conceivable property of these substances has been studied with patient care. Next, the properties of the compounds of carbon, hydrogen, and oxygen must be con- sidered, and some of the characteristics of the chemical reactions into which they enter must be discussed. For this examination the unparalleled development of the science of organic chemistry provides ample material. All of these things must be scrutinized quan- titatively as well as qualitatively, and here again there is no lack of necessary information.

Immediately one advantage of the method here proposed becomes evident. We can deal with the familiar abstractions of physical science, — specific heat, coefficient of expan- sion, solubility, heat of reaction, etc., — and thereby we shall gain all the advantages of the most exact sciences. No qualifications, no doubtful or contentious matter, no imper- fect descriptions need enter. In this manner it will be easy to estimate the absolute biological fitness in certain re- spects of water and carbonic acid, and at once a host of automatic results of their proper- ties will become evident. Many of these re- sults, such as the nearly constant temperature of the ocean, the ample rainfall, the freezing of water upon the surface, the great variety of carbon compounds, are familiar subjects of speculation, though since Darwin little in- terest has been manifested in them; others, only recently brought to light by the growth of physical science, are nearly or quite un- known in this connection. All deserve to receive more serious attention from biologists than is at present vouchsafed them, for they constitute a part of the very foundation of general biology, and they cause many of the phenomena with which man is concerned in his struggle for mastery of the environment.

Yet the mere exposition of such facts and relationships cannot suffice in a discussion of the fitness of the environment. In the first place these are in the main familiar ideas, and if they were altogether conclusive to prove the existence of really significant fitness, if they could be regarded as alone adequate to establish the necessity of putting fitness by the side of adaptation as a coordinate factor in causing the marvels of life, it is hard to be- lieve that they would have been so long neg- lected. In the second place there is nothing comparative about such information. Water is indeed a wonderful substance which fills its place in nature most satisfactorily, but would not another substance do as well ? Is not ammonia, for example, a possible substi- tute ? And are there not many other chemical bodies which might, in a very different world, serve equally useful purposes ? Perhaps, too, the great variety of carbon compounds which are known to the chemist are known only be- cause the vital processes furnish an abundance of material with which to experiment. Is it not possible, therefore, that another element, silicon, for instance, may enter into even greater varieties of compounds ? It is such questions, ever present in the minds of men of science, yet never carefully scrutinized to see if an answer be possible, which, I suspect, have long deflected attention from this subject. Clearly, therefore, it will be necessary to

compare the properties of water and carbonic acid and of the carbon compounds with those of other substances. It will be necessary to find out whether these substances are not only fit but fittest, — and this no doubt is a task of a very different sort. It may even seem at first sight an impossible one, but I hope to show that this is not the case, and that in spite of the incompleteness of our physical and chemical knowledge, it may be pressed to a satisfactory issue. A few remarks may now indicate the general line of thought we shall pursue, and then the actual study must pro- vide the proof.

The very const ant temperature of the o cean is a most important factor in the economy o f nature. It constitutes, for example, a vital regulation of the environment of a large pro- portion of all the living organisms of the world, and it has many other important "functions." This constancy of temperature is in large part due to the magnitude of the specific heat of water. Other things being equals the greater the specific heat of water, the more constant must be the temperature of the ocean. If,

then, the specific heat of water, as is actually the case, be nearly or quite a maximum among all specific heats, it follows that the fitness of water in this respect is nearly maximal. Again the ocean contains an astonishing variety of substances in solution, and they are present often in large quantities. In this manner a very great supply of food in very great variety is offered marine organisms. Of course such richness of the environment is an exceedingly favorable circumstance for the organism, and it is due principally to the ability of water to dissolve a multitude of things in large quantities. It is not to be supposed that the substances present in sea water are all of use to every organism. This need not be the case at all ; but a variety of supplies which may be adapted to special re- quirements as they arise, here iodine, there cop- per, for instance, is a very genuine advantage. Further, the vast utility of the solvent action of water in blood, lymph, and all the body fluids is too patent to call for comment. If, now, it can be shown that the eflSciency of water is nearly or quite a maximum, as it really is, among all known solvents, then it must be evident that in another respect the fitness of water is nearly or quite maximal.

quired to tear apart molecules of water, and to liberate hydrogen and oxygen, is very great indeed, and when hydrogen and oxygen re- combine to form water, this energy must reappear, — under ordinary circumstances as heat. This fact, too, is very favorable for the organism, because almost all compounds which contain hydrogen yield a great deal of energy when they are burned ; they are, in short, great reservoirs of energy which can be tapped in the process of metabolism. If, therefore, the heat of combustion of hydrogen be nearly or quite a maximum, as it is, among all sub- stances, it is clear that water is again, in an- other respect, most wonderfully fitted for life.

Finally, if it be true, and such is the case, that very few of the substances which share the fitness of water in one of these character- istics also share or approach its fitness in either of the others, and that none possesses all these qualifications in a degree that merits consideration, it must, I conceive, be admitted that so far as the investigation has proceeded water is the only possible fit substance. A criticism may here be made; are there not other substances which possess other groups of qualifications which water lacks ? And that is a difficulty which is even harder to meet. But in the first place it is evident

that there are not an infinity of important physical properties; in fact there are very few. And in the second place it is evident, both from centuries of experience in physical science and from the postulates above adopted regarding life, which undoubtedly do in the main describe its physico-chemical character- istics, that very few properties indeed are of importance in the least comparable with those which I have mentioned. Finally, it is in the highest degree probable that we are acquainted with most of the truly essential physical properties, and know them as biologically important, when they are so ; and I think we shall find it possible to consider them all, and thus to make the argument complete.

Meanwhile it should be noted that there are two different ways of illustrating the fitness of a physical property. Properly employed, both are free from fallacy, and it will be de- sirable for us to employ both. Thus it may be shown, as in the case of the temperature of the ocean, that a particular property of water, its high specific heat, automatically produces a maximum of something which is favorable to life. Or again, as in the case of the regula- tion of the temperature of the human body by the process of perspiration, it may be shown that a particular property of water, its high

heat of vaporization, has been utilized through adaptation of the organism to secure very- high efficiency in a physiological process. Such is the method which must be followed in order to decide the question of the fitness of the environment. The physico-chemical char- acteristics of water, carbonic acid, and the carbon compounds are to be taken up one by one, and their absolute and relative magnitudes considered. The possible utility of such proper- ties, both automatically and through process of organic adaptation, must then be estimated, bearing in mind the fundamental characteris- tics of the living organism which have been arbitrarily postulated. Finally the various favorable qualities of water, carbonic acid, and the carbon compounds must be grouped together in order to see if they constitute a unique ensemble of fitness, among all possible chemical substances, for a living organism which must be complex, regulated, and en- gaged in active metabolism.

At length the problem of fitness appears in a simple form. The road to a solution is open, and we may now proceed to an untram- meled discussion of unexceptionable data and well-known laws of physics, chemistry, meteor- ology, and physiology. Without further hypo- thetical difficulties, these must lead to the goal. IT was assuredly not chance that led Thales to found philosophy and science with the assertion that water is the origin of all things. Whether his belief was most influenced by the wetness of animal tissues and fluids, or by early poetic cosmogonies, or by the ever pres- ent importance of the sea to the lonians,^ however vague his conception of water may, indeed must, have been, he at least expressed a conclusion which proceeded from experience and serious reflection. Later, when positive knowledge had already grown to be a sub- stantial basis for speculation, both meteor- ological and chemical views contributed to the decision of Empedocles and Aristotle to include water among the elements.^ And it is especially worthy of note that of earth, air,

2 Windelband, I.e.; S. Gunther, "Geschiclite der Natur- wissenschaften." Reclam, Leipzig, Vol. I, p.l9. fire, and water the last is the only one which happens to be an individual chemical com- pound. From that day to this the unique position of water has never been shaken. It re&^ins the most familiar and the most im- portant of all things. Within a comparatively recent time, to be sure, it has definitely lost its claim to be a true element, in the modern sense, but meanwhile almost every great development of science has but contributed to make its importance more clear. In physics, in chemistry, in geology, in meteorology, and in biology nothing else threatens its preeminence. The physicist has perforce chosen it to define his standards of density, of heat capacity, etc., and as a means to obtain fixed points in thermometry. The chemist has often been almost exclusively concerned with reactions which take place in aqueous solution, and the unique chemical properties of water are of fundamental sig- nificance in most of the departments of his science. In geology neptunism has at length won a certain though incomplete truimph over plutonism, and the action of water now appears to be far the most momentous factor in geolog- ical evolution.^ The meteorologist perceives

1 "Of all geological agencies water is the most obvious and apparently the greatest, though its efficiency is conditioned that tlie incomparable mobility of water, which depends upon its peculiar physical prop- erties and upon its existence in vast quanti- ties in all three states of solid, liquid, and gas, is the chief factor among the propertie„v of matter to determine the nature of the phenom- upon the presence of the atmosphere, upon the relief of the land, and upon the radiant energy of the sun. Tiirough the agency of rainfall, of surface streams, of underground waters, and of wave action, the hydrosphere is constantly modifying the surface of the Uthosphere,. whUe at the same time it is bearing into the various basins the wash of the land and depositing it in stratified beds. It thereby becomes the great agency for the degradation of the land and the buUding up of the basin bottoms. . It works upon the land partly by dissolving soluble portions of the rock substance, and partly by mechanical action. The solution of the soluble part usu- ally loosens the insoluble, and renders it an easy prey of the surface waters. These transport the loosened material to the valleys and at length to the great basins, meanwhile roll- ing and grinding it and thus reducing it to rounder forms and a finer state, until at length it reaches the still waters or the low gradients of the basins and comes to rest. The hydrosphere is, therefore, both destructive and constructive in its action. As the beds of sediment which, it lays down follow one another in orderly succession, each later one lying above each earlier one, they form a time record. And as relics of the life of each age become more or less imbedded in these sediments, they furnish the means of following the history of life from age to age. The historical record of geology is, therefore, very largely dependent upon the fact that the waters have thus buried in systematic order the successive life of the ages." — Chamberlin and Salisbubt, "Geology." New York, 1904, Vol. I, p. 8.

ena which he studies;^ and the physiologist has found that water is invariably the prin- ^"Of all the terrestrial agents by which the surface of the fyl th is geologically modified, by far the most important is Water. We have already seen, when following hypogene changes, how large a share is taken by water in the phenom- ena of volcanoes and in other subterranean processes. Re- turning to the surface of the earth and watching the opera- tions of the atmosphere, we soon learn how important a part of these is sustained by the aqueous vapor that pervades the atmosphere.

"The substance which we term water exists on the earth in three well-known forms : (1) gaseous, as invisible vapor ; (2) liquid, as water; and (3) solid, as ice. The gaseous form has already been noticed as one of the characteristic ingredients of the atmosphere. Vast quantities of vapor are continually rising from the surface of the seas, rivers, lakes, snow fields, and glaciers of the world. This vapor rema;ins invisible until the air containing it is cooled down below its dewpoint, or point of saturation, — a result which follows upon the union or collision of two aSrial currents of different temperatures, or the rise of the air into the upper cold regions of the atmosphere, where it is chilled by expansion, by radiation, or by contact with cold mountains. Condensa- tion appears only to take place on free surfaces, and the formation of cloud and mist is explained by condensation upon the fine microscopic dust of which the atmosphere is full. At first minute particles of water vapor appear, which either remain in the liquid condition, or, if the temperature is sufficiently low, are frozen into ice. As these changes take place over considerable spaces of the sky, they give rise to the phenomena of clouds. Further condensation augments the size of the cloud particles, and at last they fall to the sur- face of the earth, if still liquid, as rain ; if solid, as snow or hail; if partly solid and partly liquid, as sleet. As the vapor is largely raised from the ocean surface, so in great

cipal constituent of active living organisms.^ Water is ingested in greater amounts than all measure it falls back again directly into the ocean. A con- siderable proportion, however, descends upon the landi and it is this part of the condensed vapor which we have 'now to follow. Upon the higher elevations it falls as snow, and gathers there into snow fields, which, by means of glaciers, send their drainage towards the valleys and plains. Else- where it falls chiefly as rain, some of which sinks underground to gush forth again in springs, while the rest pours down the slopes of the land, swelling the brooks and torrents which, fed both by springs and rains, gather into broader and yet broader rivers that bear the accumulated drainage of the land out to sea. Thence once more the vapor rises, con- densing into clouds and rain to feed the innumerable water channels by which the land is furrowed from mountain top to seashore.

"In this vast system of circulation, ceaselessly renewed, there is not a drop of water that is not busy with its allotted task of changing the face of the earth. When the vapor ascends into the air, it is, comparatively speaking, chemi- cally pure. But when, after being condensed into visible form, and working its way over or under the surface of the land, it once more enters the sea, it is no longer pure, but more or less loaded with material taken by it out of the air, rocks, or soUs through which it has traveled. Day by day the process is advancing. So far as we can tell, it has never ceased since the first shower of rain fell upon the earth. We may well believe, therefore, that it must have worked marvels upon the surface of our planet in past time, and that it may effect transformation in the future." — Geikie, "Textbook of Geology." London, 1903, 4th ed., Vol. I, pp. 447, 448.

^ Thus water makes up from 70 to 85 per cent of fishes, about 87 per cent of oysters, 85 per cent of apples, 78 per cent of potatoes, 95 per cent of the edible portion of lettuce, etc. other substances combined, and it is no less the chief excretion. It is the vehicle of the principal foods and excretory products, for most of these are dissolved as they enter or leave the body.^ Indeed, as clearer ideas of the physico-chemical organization of proto- plasm have developed it has become evident that the organism itself is essentially an aqueous solution in which are spread out col- loidal substances of vast complexity.^ As a result of these conditions there is hardly a physiological process in which water is not of fundamental importance.

All of these circumstances, which completely justify the interest in water which Thales and Aristotle, and nearly all later students of nature have manifested, depend in great part upon the quantity of water which is present out- side the earth's crust, and upon its often, unique physical and chemical properties. * Properly speaking, the entrance of the foods into the body is across the wall of the intestine; at this point the foods have all undergone digestion and are almost exclu- sively in solution. In like manner excretion takes place across the renal epitheUum, or the epithelium of the lungs, or across that of the sweat glands ; these too are traversed only by substances in solution.