The Fitness of the Environment

It must be remembered, however, that such conclusions depend upon reasoning from analogy, a dangerous proceed- ing. We may now return to the problem of the fitness of the environment. So long as ideas of the nature of living things remain vague and ill-defined, it is clearly impossible, as a rule, to distinguish between an adaptation of the organism to the environment and a ease of fitness of the environment for life, in the very most general sense. No doubt there are clear instances of both phenomena which require no close analysis for their interpreta- tion. Thus the hand is surely an instance of adaptation, and the anomalous expansion of water on cooling near its freezing point an instance of environmental fitness. But how much weight is to be assigned to adapta- tion and how much to fitness in discussing the relations between marine organisms and the ■ ocean ? Evidently to answer such questions we must possess clear and precise ideas and definitions of living things. Life must by ar- bitrary process of logic be changed from the varying thing which it is into an independ- ent variable or an invariant, shorn of many of its most interesting qualities to be sure, but no longer inviting fallacy through our

Such is the purpose, and the justification, for setting up the postulates of complexity, regulation, and metabolism as inherent in that mechanism which is called the living organism. With them, at length, we face the problem-which awaits us. To what ex- tent do the characteristics of matter and energy and the cosmic processes favor the existence of mechanisms which must be com- plex, highly regulated, and provided with suitable matter and energy as food ? If it shall appear that the fitness of the environment to fulfill these demands of life is great, we may then ask whether it is so great that we can- not reasonably assume it to be accidental, and finally we may inquire what manner of law is capable of explaining such fitness of the very nature of things.

AN examination of the relationship be- tween Uf e and the environment, in which by means of the simphfying postulates pre- viously developed life is arbitrarily taken as an invariant, should, if it is to be quite general, rest upon a physico-chemical description of the whole universe. We require to know the form and structure of stars and of interstellar space, of nebulae and of solar systems, and the conditions and changes which accompany such aggregations of matter. Evidently this requirement can be but imperfectly fulfilled, and yet one need not be too apologetic in venturing the attempt. In the end, to be sure, we shall found our argument upon the safe basis of terrestrial phenomena, but mean- time it will be an advantage to consider con- ditions far and wide.

The science of cosmography is probably the earliest of all the natural sciences, and cosmological speculation appears to accom- pany it from the outset. Long before the dawn of history the Chaldeans possessed much accurate information about the stars, and the zodiac was known to the Egyptians not less than fifteen centuries before our era. Always pursued with great interest, such studies received their first provisional systematic for- mulation at the hands of Hipparchus in the second century B.C. He, the greatest of the astronomers of antiquity, succeeded in bring- ing the apparent movements of the sun, moon, and planets into an arbitrary scheme which was nearly perfect for the sun, though less so for the other movable celestial bodies. He also measured and catalogued the positions of a large number of fixed stars. Upon this secure foundation of quantitative observa- tions modern astronomy has built. At the beginning of the modern period Copernicus, Tycho Brahe, Kepler, Galileo, and Newton reduced the phenomena of the solar system to law. At a later day speculations based upon their results and upon growing knowl- edge of physics and chemistry led Thomas Wright, Kant, and finally Laplace to a ra- tional, if somewhat imperfect, cosmological

theory of the solar system. Finally, ever more accurate observations and the marvel- ous fertility of spectroscopical investigations have brought the stars within our reach. The whole universe now appears to be not unlike our part of it, both chemically and physically. The same forms of matter, the same material aggregates, the same manifes- tations of energy, and similar movements are everywhere present. The stars are no longer changeless, but violently active bodies ; they are no longer permanent, but evolving sys- tems ; they are born, they grow, age, and die; and throughout their evolution they obey laws, which, though as yet imperfectly known, appear to be common to all. Mean- time the study of nebulae, comets, and meteor- ites has kept pace with other departments of the science, and our interpretation of the re- sults of stellar astronomy ^ constantly gains from ever increasing knowledge of the physical and chemical processes in the sun.

The universe which thus gradually has been revealed to the astronomer is made up of a relatively small number of types of material ^ A description of such facts from the physico-chemical point of view may be fomid in Arrhenius's "Lehrbuch der kosmichen Physik." Leipzig, 1903. A brief popular account of some of the facts in the same author's " Worids in the Mak- ing," translated by Boms. New York and London, 1908. aggregation. These include luminous dense bodies like the sun and stars; non-luminous dense bodies like the earth, the moon, the planets, and invisible partners of certain stars ; nebulae, comets, and meteorites. The larger of these bodies are separated by vast extents of space which contain only rare meteorites, perhaps minute traces of gaseous material, and cosmic dust. There can be little doubt that other types of bodies do not commonly occur in that portion of the universe which is open to astronomical investigation. Both the enormous collections of astronomical data which are now at hand and the beginnings of clear knowledge of cosmic processes justify this belief. Of what may lie beyond the visible stars we can, of course, know nothing.

The nature of the stars is revealed to us chiefly by study of their spectra, according to which they have been roughly classified, by Vogel ^ for example, quite simply into three principal types. I. White stars in which there is marked evidence of the presence of hydrogen, or, in some instances, helium. The stars of this class undoubtedly are extremely hot, the helium stars probably especially so. Their atmospheres seem to be very dense and to consist of hydrogen or helium or a mixture of the two gases. There is evidence that some of these stars possess very high rotational velocities.

II. Yellow stars, including the sun, whose spectra indicate the presence of hydrogen and numerous metals, — sodium, iron, calcium, magnesium, etc. The lines which show the presence of hydrogen in the stars of this type vary in intensity. The current belief is that those stars which appear to possess more hydrogen are the hottest. The stars of this type are less hot than those of type I. III. Reddish stars whose spectra show little or no sign of the presence of hydrogen, but indicate that of chemical compounds, in- cluding hydrocarbons. The presence in these spectra of the lines of sodium, iron, calcium, and magnesium is clearly established. Stars of this type are evidently the coolest of lumi- nous dense bodies.

This classification is, of course, provisional and unsatisfactory, and probably sometimes results in bringing together relatively unlike stars and in separating such as are very much akin. Moreover, subdivisions in the classifica- tion are necessary and hard to make. Other better but more complex classifications appear to exist, but they suflFer only in less degree from like defects. In short all the known facts can best be explained by the assump- tion that the stars represent different stages of development of suns.^ In that case this

1 "Bei Durchmusterung der Specktra der verschiedenen Sterne kann man sich nicht des Gedankens erwehren, dass die verschiedenen Sterngruppen verschiedenen Entwick- lungsstadien entsprechen. Die jungsten und warmsten aller Sterne wUren (nach der allgemeinen Ansicht, vgl. weiter unten Kap. Kosmogonie) diejenigen der ersten Gruppe. Das kontinuierliche Licht, welches von dem eigentlichen Stemkorper ausstrahjt, rlihrt haupstfichlich von Kondensa- tionen, wolkenartigen BUdungen in der Atmosphare der Sterne, zum geringeren Teil von den stark verdichteten Metalldampfen im Inneren des Sterns her. In den hbheren Schichten dieser Atmosphare finden sich die leichten Gase, WasserstoEE oder Helium oder aUe beide, weiter unten Metall- dampfe. Bei den Sternen erster Klasse ist die Atmosphare der leichten Gase so dick und heiss, dass die fUr uns sicht- baren Kondensationen beinahe alle in diesen oberen Schichten vor sich gehen. Wir sehen deshalb keine oder nur schwache MetalUinien, dagegen sehr starke Wasserstoflf- oder Helium- linien. BisweUen ist die Menge und Temperatur der leichten Gase genUgend, um helle Umkehrungen dieser Linien zu verursachen. Bei dem zweiten Spektraltypus ist die Ab- kUhlimg weiter fortgeschritten, so dass Kondensationen nicht nur in den hochsten Schichten der Atmosphare, sondem auch innerhalb der Metallatmosphare vorkonmien. Man sieht dann die dunklen MetalUinien scharf hervortreten. Das Zurllcktreten des violetten Endes des Spektrums und einige schwache BSnder im roten Tefl deuten auf niedrigere Tem- peratur hin. Bei den rotlichen Sternen treten tiefe Temper- atur andeutende Erscheinungen noch mehr hervor. Die bei denselben gewohnlich vorkommende Veranderlichtkeit lasst auf das Vorkommen von kalteren und warmeren Perioden

development or evolution must be a contin- uous process through which every sun slowly passes, and on the whole all suns must be much alike. Certainly we have the best of evidence to justify the assumption that most stars, including the sun, have very much the same chemical composition, and that differ- ences in spectra are due to the slowly progress- ing physico-chemical changes which have accompanied the process of cooling. Needless to say, the chemical composition of the sun itself is far better known than that of the stars. Particularly prominent among his constituent elements are those above mentioned: hydrogen, sodium, calcium, mag-

schliessen, wie solche in geringerem Maasstab bei unserer Sonne durch die Fleckenperiode sich kundgeben. Zuletzt wird die Leuchtkraft der Sterne sekr schwach und das Licht ausgepragtrot, der relativ niedrigen Temperatur entsprech- end. Nach diesem Stadium kommt dasjenige, worin die dunklen nltraroten StraHen allein henrschen, der Stem ist in einen nichtleuchtenenden Himmelskorper Ubergegangen (vgl.* weiter unten Kap. Kosmogonie). Im Grossen und Ganzen zeigen die Sterne dieselbe chemi- sche zusammensetzung wie die Sonne. Die hervorragende Eolle des Wasserstoffs und Heliums, sowei des Eisens, Na- triums, Calciums und Magnesiums, macht sich uberall be- merkbar. Es ist dann kein Zweifel, dass unsere Sonne mit den Fixsternen sehr nahe verwandt ist, und zwar ist sie als ein Fixstern der ersten Abteilung in der zweiten Klasse an- zusehen." — Abehenius, "Kosmische Physik." Leipzig, 1903, p. 27.

nesium, and iron. Also some others, which because of their low density are concentrated near the surface, are known to occur. The elements which have not yet been discovered are those like the metalloids which do not un- der ordinary circumstances give well-marked spectra, and those like gold, platinum, and mercury, whose higher specific gravities may be supposed to cause their accumulation in the interior. Carbon is certainly present, and almost certainly oxygen as well. Indeed it is only reasonable to conclude, as Kirchhoff originally suggested,^ that all the elements

* "Diese Vorstellung von der Beschaffenheit der Sonne stimmt mit der von Laplace begriindeten Hypothese Uber die Bildung unseres Planetensystems uberein. Wenn die Masse, die jetzt in den einzelnen Korpem dieses Systems verdichtet ist, in fruheren Zeiten einen zusammenhangenden Nebel von ungeheurer Ausdehnung bildete, durch dessen Znsanunenziehung Sonne, Planeten und Monde entstanden sind, so mussten alle diese Kbrper bei ihrer Bildung im wesentlichen von ahnlicher chemischer Zusammensetzung sein. Die Geologie hat gelehrt, dass die Erde einst in glU- hend fliissigem Zustande sicli befunden tat ; man muss anneh- men, dass auch die anderen Korper unseres Systems einmal in einem solchen gewesen sind. Die AbkUhlung, die infolge der Ausstrahlung der Warme bei aUen eingetreten ist, hat aber bei ihnen sehr verschiedene grade erlangt ; und wShrend der Mond kalter als die Erdegeworden ist, ist die Temperatur des SonnenkSipers noch nicht unter die Weissgluhhitze gesunken. Die irdische Atmosphare, die jetzt nur wenige Elemente enthalt, musste, als die Erde noch gliihte, eine viel mannigfaltigere Zusammensetzung haben ; alle in der GlUh-

are present in the sun, and very often, at least, in the stars. Exceptions may arise, but probably they will hardly suffice to invalidate the rule. The large, dark, dense bodies which are directly known to us are the planets and their satellites. There are, however, many in- dications that the heavens are occupied by great numbers of "dead" suns, incrusted and therefore no longer luminous. Such appear to be the only conclusions which can be drawn from a study of the energetics of solar evolu- tion, for sooner or later a sun must cool from loss of energy until at length a crust forms, and, barring catastrophe, it must then endure for- ever. Moreover, as we have seen, the varying aspects of the stars seem to disclose suns in all stages of such a process.

More nearly direct is the evidence furnished by study of variable stars of the Algol type. Algol itself (/S Persei) is a star of second magnitude with a period of 2 days, 20 hours, 48 minutes, 53.8 seconds. During each period hitze fluchtigen Stofife mussten in ihr vorkommen. Eine entsprechende Beschaffeaheit muss heute noch die Atmosphere der Somie besitzen." — G. Kihchhoff, — " Untersuchungen liber das Somienspektrum und die Spektren der Chemischen Elemente." Abhandlungen der Koniglichen Akademie der Wissenschaften zu Berlin, 1861. Zweite, durch einen An- hang vermehrte Ausgabe. Berlin, 1862.

for about 2j days it shines with constant in- tensity; thereupon it begins to decline and in approximately 4^ hours sinks to its minimum of brightness; then it becomes gradually brighter until after 4^ hours more it has re- attained its full brilliancy. This behavior is explained by the supposition that Algol is accompanied by a dark star and that their movements are such that a partial eclipse occurs every 69 hours. Pickering has suc- ceeded in calculating, upon the assumption that the dark star as a whole intercepts the rays of Algol, the approximate sizes, veloci- ties, and orbits of these two stars, one of which is quite invisible. Many similar phe- nomena lead to similar conclusions regarding other variable stars.

It is apparent that such dark bodies, whether extinct suns or planets, represent another stage in celestial evolution. Their past his- tories may be various, for there is still room for much doubt as to the manner of formation and origin of planets, but at any rate all are probably derived from luminous stars or planets through the process of cooling, with its accompanying crust formation. Like their earlier forms, they must therefore be made up of matter as we know it, since when a heavenly body puts on a crust, it does not change the

matter of which it is composed. Finally terrestrial chemistry completes the evidence regarding the composition of such astronom- ical bodies; geophysics that regarding their state. The number of extinct suns is prob- ably very great ; Arrhenius thinks it not un- likely that they may be one hundred times more numerous than the luminous stars.^ It is more difficult to gain a clear idea of the nebulae, for such aggregations of matter are very diverse in appearance, and none lie near enough to the earth for us to study them as we study the solar system. However, in- vestigation of new stars, of the spiral forms of many nebulae, of the so-called star rifts which appear to be due to the movement of a large body through a nebula, sweeping up smaller bodies and leaving a channel behind, and a variety of considerations dependent upon the modern development of the sciences of physics and chemistry, all contribute to a growing belief that nebulae may often, and sometimes at least do certainly arise from col- lisions between dense bodies. Further, the nature of the processes by which stars may be formed out of nebulae becomes constantly better understood, and while there is small ground to regard our present science of nebulae

as final, there is none at all for the belief that anything essentially inexplicable either physico-chemically or genetically will be dis- covered in their organization. Putting aside all contentious matters, it is abundantly clear that nebulae, however they may vary among themselves, are made up of vast extents of gaseous material and dust which are exceedingly rare and at very low temperature, and that they may contain all kinds of foci of condensation, from stars to meteorites, in great variety of forms and conditions.

On the whole the common-sense judgment that the solar system may be taken as a fair sample of the universe, and that its probable evolution is in the main typical of cosmic evolution in general seems to be well founded. Any other hypothesis does violence to a host of facts, and .to the larger generalizations of modern science. If now we seek to make the best of existing astronomical knowledge, as hastily sketched, in the study of our biological problem, cer- tain considerations at once present themselves..

Obviously it is not everywhere in such a uni- verse that life can exist. The visible stars, like the sun, certainly cannot support life. Throughout such bodies durable and complex arrangements of matter are impossible, for if formed, they must be at once dissipated by catastrophes far greater than any which can occur upon the earth's crust. The enormous intensity of heat, even in the most superficial parts of suns, must effectually preclude any state of matter but the gaseous, and thus prevent the existence there of anything of the nature of a mechanism. Such bodies, apart only from continuous variation from center to periphery, in the proportions of the elements, in density, and in the nature of the chemical unions between the elements, must be essentially homogeneous. They can scarcely possess relatively as much structure as the earth's atmosphere. In truth the sun itself seems to be the one and only durable solar mechanism.

Not less evident is the impossibility of active life in interstellar space or in nebulae. Dor- mant life (panspermia) may indeed be possible universally, except only in the neighborhood of suns. But if life is to be fed, if there is to be active metabolism, including exchange of matter with the environment, something more nourishing than the rare molecules of a nebula, or the still rarer particles of interstellar space, must be provided. We may safely conclude, therefore, on the basis of our reliable knowledge of the universe, that active life can exist probably only upon a dense, crusted body ^; for, of course, the in- terior of the earth is no better suited to life than is the interior of the sun.

We have perhaps taken a long road to arrive at so familiar an idea. But our task involves the consideration of every conceivable form of life, not merely that relatively anthropo- morphic kind which we commonly think of when speculating loosely regarding life in other worlds. It is indeed possible that the common-sense judgment of the universe which declares our solar system to be on the whole, in its funda- mental characteristics, typical of every such system may turn out to be in some respects unjustified. For the present, however, so long as we use it only as an indication of the direction in which we are to turn our atten- tion, there is certainly no risk whatever in fol- lowing this hypothesis in the later discussion.

' For an interesting discussion of the necessary conditions of existence see P. Lowell, "Mars as the Abode of Life." The Macmillan Company, New York, 1908. Let us, accordingly, now examine such phenomena as are likely to occur upon the surfaces of bodies which in the course of cosmic evolution have acquired a solid crust. In faithfully carrying out such a plan, the sciences of geology and meteorology must be brought under contribution, and climatic conditions must receive especial attention. Not, to be sure, that our globe in every respect can fairly be taken as meteorologically typical of all incrusted bodies. On the contrary, there are a large number of phenomena which are unquestionably of highest significance in fa- voring the existence of life on this particular planet which appear to be accidental and prob- ably somewhat uncommon.^ Such are the

* These also have been favorite subjects in the works on natural theology. The Bridgewater Treatises of Whewell and of Prout are replete with illustrations, those of Whewell often moderately expounded, while Front's are, as a rule, most curious and antiquated. "Lastly, who will venture to assert that the distribution of sea and of land, as they now exist, though apparently so disproportionate, is not actually necessary as the world is at present constituted ? What would be the result, for instance, if the Pacific or the Atlantic oceans were to be con- verted into continents ? Would not the climates of the exist-

size of the sun taken in relation with, its dis- tance from the earth; the size of the earth, which enables it to retain its present atmos- phere; the eccentricity of its orbit and the inclination of the ecliptic; the relative amounts of land and sea, and a host of other factors. Together these probably make of the earth, in comparison with other bodies, an extremely favorable abode for the living organism. Yet it cannot be denied that in detailed chemical constitution the earth is certainly more or less typical of all similar bodies. Moreover the earth's crust and its atmosphere, being formed in accordance with

ing continents, as formerly observed, be completely changed by such an addition to the land, and the whole of their fertile regions be reduced to arid deserts ? Now, this distribution of sea and of land, so wonderfully adapted as it appears to be to the present state of things, depends of course ia a great measure upon the absolute quantity of water in the world. While, on the other hand, the relative gravity of water, as com- pared with that of the earth, keeps the ocean within its destined limits, notwithstanding its incessant motion. Thus Laplace has shown that the world would have been con- stantly liable to have been deluged from the slightest causes, had the mean density of the ocean exceeded that of the earth ! Hence the adjustment of the quantity of water and of its density, as compared with that of the earth, afford some of the most marked and beautiful instances of design," — Phout, The Bridgewater Treatises, Treatise VIII, "Chemistry, Meteorology, and the Function of Digestion." London, 1834, pr,-^l«6-187.

general laws, are likewise typical or at all events were so at the time of their origin. Neither can the change in crust and atmos- phere which time has wrought be wholly unique, though here a possible exception may again arise in the action of life itself. Since we do not at present positively know of the existence of life elsewhere and certainly have no detailed knowledge of its nature, we can- not feel sure that the conversion of atmos- pheric carbonic acid into oxygen and coal is either a universal or a common occurrence. In details of the geological process indeed there may well be marked differences. Probably the greatest variation will occur in the relative duration of conditions like those , which we now enjoy on the earth, the length or brevity of the period from the full establishment of the circulation of water by evaporation, cloud formation, rainfall, with the flow of lakes and streams, until its extinction by cold. Thus there is more liability of error in an analyis of the general characteristics of those spon- taneous changes which must occur upon the surface of a body after the formation of a crust than there is in the attempt to dis- cover the general characteristics of stellar evolution. But here again our knowledge is not based upon terrestrial phenomena «lone.

With greater or less completeness and accu- racy the atmospheres of the moon, of Mars, and of other planets have been studied and accounted for. Even at the earliest period in the evolu- tion of a typical star there appears to be a progressive variation in chemical composi- tion from center to periphery. Theoreti- cally it seems inevitable that the heaviest elements should be concentrated in the interior and that those of lowest atomic weight should be present in greatest amount near the sur- face. Actually, as above stated, spectro- scopic investigation fully confirms this view. Thus the spectra of typical hot stars show that hydrogen is an invariable constituent of their superficial parts. Indeed the uni- versal presence of hydrogen under such cir- cumstances is undoubtedly one of the most clearly established facts of stellar astronomy. As stars cool and become red the spectral changes quite as unmistakably point to the presence of carbon. Accordingly we possess the best of evidence and the best of reasons for the belief that large quantities of hy-