The Fitness of the Environment

^ "Der Organismus, Pflanze wie Tier, ist ein GefSss voU wassemer Losung, in dam sich als disperse Phase v^rschieden- aj-"^" ^oide befinden." — Bechhold, "Die KoUoide in be que^ Medizin." Dresden, 1912. ^uch properties are our present concern. Doubtless if it were not for the enormous quantity of water which exists upon our planet, all its physical properties would be of little avail to bring about its universal^im- portance in nature. This, however, as has been above explained, appears to be neither an accidental nor an uncommon phenomenon. Of the total extent of the earth's surface the oceans make up about three fourths, and they contain an amount of water sufficient, if the earth were a perfect sphere, to cover the whole area to a depth of between two and three miles. This corresponds to about 0.2 per cent of the volume of the globe. The occur- rence of water is, moreover, not less important and hardly less general upon the land. In addition to lakes and streams, water is al- most everywhere present in large quantities in the soil, retained there mainly by capillary action, and often at greater depths. The atmosphere also contains an abundance of water as aqueous vapor and as clouds. NowS the very occurrence of water upon the earth, and especially its permanent presence, is due in no small degree to its chemical stability in the existing physical and chemical con- ditions. This stability is of great moir'^^t in the various inorganic and organic T^ ettut,^.

in which water plays so large a part. In the first place the chemical reactions in which it is concerned during the process of geological evoljLition, though they are no doubt in the total of great magnitude, are both slow and far from violent. Long since any very active changes of this sort, so far as the superficial part of the crust is concerned, have run their course. In the second place water is really, at the temperature of the earth and in com- parison with most other chemical substances, an extremely inert body, for the union of hydro- gen with oxygen is so firm that it is not readily dissolved.

Thus water exists as a singularly inert con- stituent of the atmosphere, as a liquid nearly inactive in chemical processes on the surface and in the soil, and everywhere as a mild sol- vent which does not easily attack the sub- stances which in great variety dissolve in it. The chemical changes which do follow upon solution are not such as to produce substan- tial chemical transformations, and most sub- stances can pass through water unscathed. The nature of water, then, is a great factor in the chemical stability, which, no less than the physical stability of the environment, is es- sential to the living mechanism. But it may be questioned if such stability would not

necessarily be ultimately attained in greater or less degree with almost any other substance, as a result of the general tendency of chemical processes to reach a condition of equilibrium, and it will therefore be well to turn to more secure fields of inquiry. The most familiar among such are certain characteristics of water which have been long known, and which, as the Bridgewater Trea- tises and other works on natural theology testify, were formerly favorite subjects of metaphysical speculation, — the thermal prop- erties. These characteristics of water were recognized at an early stage in the develop- ment of modern science, and in many cases their special importance in meteorology and in other departments of the sciences of nature is almost self-evident.

First among these is the heat capacity or, as it is more commonly termed, the specific heat of water. This quantity has the value of 1.000 for th'i interval between 0° and 1° centigrade, a number which is due to the choice of water in defining the calorie or fundamental unit of heat. The calorie, small calorie, or gram . calorie is that quantity of heat which is required to raise the temperature of one gram of water through 1° centigrade, and it varies slightly with the temperature, having the relative values 1.000 for the in- terval from 0° to 1°, 0.998 for the interval from 4° to 5°, 0.992 for the interval from 15° to 16°, and its mean value for the interval from 0° to 100° is 1.004. The heat capacity of water is then 1.000, in that 1.000 calorie is re- quired to raise the temperature of 1.000 gram of water through 1.000 degree centigrade.

The approximate specific heats of a variety of important substances are as follows: — It is unnecessary to enter upon an elaborate analysis of the data concerning specific heats, for the magnitude of the specific heat of a substance is dependent upon its chemical nature, as was first made clear by Dulong and Petit in 1819. The law wb'cli bears their name consists of the statement that in the case of elementary substances the product of specific heat and atomic weight is a constant, — roughly, 6.4. Certainly this so-called raw is a mere approximation, aiid some elements, notably carbon, silicon, and boron, at the ordinary temperature, depart widely from its requirements, but in the main the approxi- mation holds good. Later the researches of Neumann, Garnier, Cannizaro, and especially of Kopp made possible an extension of the law to compounds.

It is evident that the law of Dulong and Petit amounts to the statement that for all elementary substances the quantity of heat which is required to change the temperature of every atom, regardless of its nature, is a constant. A brief discussion will serve to make this plain. According to the law the specific heat of an element varies inversely as its atomic weight, diminishing as the atomic weight increases, so that the product of the two quantities remains constant. But of course the number of atoms per gram of sub- stance also varies inversely as the atomic weight. Hence the specific heats of elemen- tary substances and the number of atoms per gram are always roughly proportional, which

can only be the case if all atoms, no matter of what element, require a constant amount of heat to raise their temperatures one degree. That is to say, in all elementary substances the heat capadty oLttm atom I's ppristaTit^ and independent of the nature of the element (with the qualifications above noted). The study of compounds has shown that this same generalization is also true of them. This means that in all substances the heat capacity of every atom is nearly constant and is independent of its nature and of that of the compound in which it finds itself.

Accordingly the law of Dulong and Petit may be formulated as follows ; — the specific heat of a substance multiplied by the average of the atomic weights of all the constitutent atoms in the molecule is often equal to about 6.4, and is always not very different from this number. This conclusion may be tested with the data above recorded. It must be confessed that such, data are not a briUiant confirmation of the law. A series of numbers which vary from 2.0 to 6.0 is something quite different from constancy, and every one of these numbers is less than 6,4. It is, however, certain that these quanti- ties are uniformly of the same order of magni- tude, and this is all that is of importance for our present purpose. For accordingly they prove that unless the average atomic weight of a substance be very low its specific heat cannot be very high. Of course only com- pounds which are largely made up of hydrogen can possess very low average atomic weights, and among such those will be lowest in this respect which contain a relatively small number of atoms of another element of low atomic weight, like carbon, nitrogen, oxygen, etc. Of such substances the hydrocarbons make up the only numerous group, and for the most part their specific heats appear to be, like that of elementary carbon itself, considerably lower even than would be predicted by the rule. So it is that the conclusion is warranted that water shares the characteristic of very high specific heat with a very small number of substances, among which hydrogen and am- monia are probably the only important chemi- cal individuals. From this conclusion another

follows directly ; namely, that water possesses certain nearly unique qualifications which are largely~respon^le for maHng the earth habitable, or at least very favorable as a habitation for living organisms. It need hardly be pointed out that this importance of the h igh heat__ eapaeity-€>£-water is a very well-known fact. Even in the early decades of the nineteenth century, when natural theology and argument from design were the subject of lively controversy, es- pecially in England, such subjects were very familiar, and an excellent temperate dis- cussion from the theologian's side will be found in Whewell's Bridgewater Treatise.^ At that time, before a clear formulation of the concept of adaptation existed, it was of course impos- sible to disentangle such natural fitness from the results of the organic evolutionary process. In the more modern period since the publi- cation of "The Origin of Species," the late Professor J. P. Cooke of Harvard has dwelt upon this and other properties of water and sought to show that, lying wholly apart from the new ideas, such phenomena remain

* Chapter IX of this work deals with "The Laws of Heat with Respect to Water." Although the ideas are somewhat vague, the importance of the capacity of water to absorb heat is cleairly brought out. unexplained and inexplicable by our present laws of natural science. He, too, endeavored to employ such facts as theological arguments but, in spite of many sound contentions, with less success in a more skeptical age.^ The most obvious effect of the high specific heat of water is the tendency of the ocean and of all lakes and streams to maintain %jiearly coTistant temperature. This phenomenon is of course not due to the high specific heat of water alone, being also dependent upon evaporation, freezing, and a variety of cir- cumstances which automatically mix and stir water. But in the long run the effect of high specific heat is of primary importance. It will be convenient to postpone considera- tion of the regulation and importance of the constant temperature of the ocean until the other properties of water which contribute thereto have been discussed.

' "Assume that the variations preserved by natural selec- tion are all accidental, a point on which naturalists greatly differ, still what is the result ? An adaptation to the environ- ment. According to the theory, then, the conditions of the environment are a determining cause ; and unless we believe that all nature was the result of a fortuitous concourse of atoms, we can find in these conditions abundant opportunities where intelligent causation can act." — Josiah Paksons Cooke, "The Credentials of Science." New York, 1888, p. 251.

water is the moderation of both summer and winter temperatures of the earth. It is not easy to estimate the total magnitude of this effect, but the manner in which it comes about is well illustrated by the differences between seaboard and inland climates or between the climate of a large part of the United States, which is a continental climate, and that of Western Europe, which is essentially an in- sular climate. In the most extreme form such moderation of climate is to be observed on the high seas and upon small islands. There are found the smallest known differences between the mean temperatures of diflFerent months of the year and of different hours of the day, and the least tendency to violent changes of temperature. The calculation of Zenker regarding normal temperatures may

be. cited as a good illustration of the nature of the case.^ It is unnecessary to discuss the efiFects upon living organisms of the equable tepi- perature of the ocean and of the moderation of climate, for obviously we are here confronted by a true instance of regulation of the environ- ment. The high heat capacity of water operates in still another manner to regulate tempera- ture upon the land and at the same time to increase the mobility of the environment of marine organisms. For directly or indirectly it is involved in the formation and duration of ocean currents, especially the movement of water in the depths from the polar to the tropical seas, and it determines the amount of heat carried by such currents. A similar and even more important "function" is the direct promotion of winds, with the resulting distribution of aqueous vapor throughout the atmosphere, a primary factor in the dissemina- tion of water by means of the rainfall. Here the essential thing is the existence of a vast warm reservoir in the tropics and of two similar cold reservoirs at the poles. Under

' A discussion of Zenker's work will be found in Hann's "Handbook of Climatology," translated by Ward, pp. 210- these circumstances the circulation of winds, bearing away water vapor from the tropical oceans, is inevitable, and the process is intensified by the high specific heat of water. , The living organism itself is directly favored by this same property of its principal constit- uent, because a given quantity of heat pro- duces as little change as possible in the tem- perature of its body. Man is an excellent case in point. An adult weighing 75 kilo- grams (165 pounds) when at rest produces daily about 2400 great calories, which is an amount of heat actually sufficient to raise the temperature of his body more than 32° centigrade. But if the heat capacity of his body corresponded to that of most substances, -the same quantity of heat would be sufficient to raise his temperature between 100° and 150°. In these conditions the elimination of heat would become a matter of far greater difficulty, and the accurate regulation of the temperature of the interior portion of his body, especially during periods of great muscular activity, well-nigh impossible. Extreme con- stancy of the body temperature is, of course, a matter of vital importance, at least for all highly organized beings, and it is hardly conceivable that it should be otherwise. In

the first place marked influence of change of temperature upon chemical reaction is almost universal, and as a rule an increase of 10° centigrade in temperature will more than double the rate of a chemical change.^ Sec- ondly all living organisms contain both chemi- cal substances and physico-chemical struc- tures or systems which begin to be altered, and usually irreversibly altered, at a tempera- ture which is very little above that of the human body.^ It is perhaps imaginable that

^ If the velocity of a chemical reaction be represented by a coefficient, h, the increase in its magnitude with rising tem- perature is unlike that of ordinary physical coefficients, and in many cases amounts to a two or threefold rise for a tem- perature increase of 10° centigrade. The well-known data concerning the transformation of dibromsuccinnic acid into brommaleic acid and hydrobromic acid in aqueous solution illustrate a typical case. ^ This is attested not only by the low temperature at which many proteins coagulate, but also by the action of temperatures between 50° and 60° to inactivate enzjmies, and

conditions might be otherwise in beings of a very different kind, but to-day every chemist well knows that if he is to control a chemical process, almost the first desideratum is rigid regulation of the temperature at which the process takes place.^ It is therefore incontestable that the un- usually high specific heat of water tends automatically and in most marked degree to regulate the temperature of the whole envi- ronment, of both air and water, land and sea, and that of the living organism itself. Like- wise the same property favors the circulation of water by facilitating the production of winds, besides contributing to the formation of ocean currents. Here is a striking instance of natural fitness, which in like degree is un- attainable with any other substance except ammonia.

to produce alterations in many of the complex substances that are involved in the phenomena of immunity and other similar things. 1 Almost the most conspicuous change in the equipment of modem chemical laboratories, as a result of the growth of physical chemistry, is the introduction everywhere of thermo- stats. Very different from specific heat in their relationship to the chemical constitution of a substance, but not unlike it in biological importance, are the so-called latent heats of melting and of evaporation.

The latent heat of melting is expressed as the number of calories which are required to convert one gram of solid at the freezing point into one gram of liquid at the same tempera- ture. For water its value is approximately 80, which indicates that the same quantity of heat must be employed to melt ice as to raise the temperature of the resulting ice- water to 80° centigrade. The latent heat of evaporation is similarly defined as the number of calories required to change one gram of liquid into vapor. Its magnitude depends upon the temperature at which the process takes place. The latent heat of evaporation of water is approximately 536. There is required, accordingly, as much heat to boil away one gram of water as to raise the temperature of 536 grams through 1° centigrade.

the high latent heats of fusion and evapora- tion of water upon the meteorological pro- cesses. When, for example, a body of water becomes cooled to its freezing point, the further abstraction of heat cannot lower its temperature below that point, which, to be sure, is somewhat variable in the case of salt water. And so long as water and ice exist in contact, the system constitutes a ther- mostat, a very accurate one if the water be fresh, which changes only in respect to the quantities of ice and water as heat is added or removed.^ Heating serves merely to melt the ice, cooling to freeze the water. Accord- ingly, as long as the earth shall remain habit'- able the cooling of its oceans and seas will remain rigidly limited by their freezing point. However inclement the atmosphere, the ocean can always support life until the final extinc- tion of water by cold. It is worthy of note that the freezing point of water, though to man with his carefully regulated body tem- perature apparently low, is in reality very high indeed compared with that of any like substances, — perhaps 100° centigrade above the average.

* In fact, there is no better means of obtaining a constant temperature in the chemical laboratory than by mixing pure ice with pure water. Hydride of antimony . Hydride of arsenic . , Hydrobromic acid . , Hydrochloric acid . , Hydrofluoric acid . . Hydriodic acid . . . Carbon dioxide . . . Hydride of phosphorus Hydrogen sulphide . . Sulphurous oxide . . . This is, no doubt, one of the most important facts with which we are concerned, for while a very large number of chemical processes take place quite freely at 0°, the conditions are very different at the freezing point of am- monia, for instance. At that temperature the velocity of most chemical processes is but a fraction of one per cent of their velocity at 0°, and a large part of the chemical activity which is familiar to us ceases.

The result of the unusually high freezing point of water and of the phenomenon of latent heat is felt, however, not merely in the avoidance of an excessive fall in the tempera- ture of lakes and seas. As above explained. whenever the ocean comes in contact with cHmates of very low temperature it tends to moderate them, the more effectively the greater the disparity between the temperature of the air and that of the water, and here latent heat is quite as important a factor, though indirectly, as specific heat.

It remains to point out that the latent heat of melting of water is nearly the greatest which has yet been discovered, being ex- ceeded, in fact, by that of ammonia alone. Lead . . Bromine . Cadmium . Iron . . . Gallium . Iodine Potassium . Copper . . Sodium Nickel . . Palladium . Phosphorus Platinum . Mercury . Sulphur . Silver . . Bismuth . Zinc . . . Tin . . . Accordingly, the processes above described possess nearly the highest possible eflSciency. A very large amount of heat must be ab- stracted from a body of water before it can be solidified; after a given amount of cool-

ing a very large quantity of water must re- main liquid; a body of water at 0° centi- grade can warm up a very large amount of colder air with the formation of a very small quantity of ice. Thus the permanency of the ocean, and the moderating eflEect of water upon cold climates are very nearly maximal. These are also facts, directly dependent upon the physico-chemical nature of water, which are remarkably favorable to the organism. Still more important is the latent heat of evaporation of water. Wherever water is in contact with the air, evaporation must take place until, if the system be of small dimen- sions, equilibrium is established between aque- ous vapor and the liquid; in short until the air is saturated with water. Unlike freezing, which occurs only at one particular tempera- ture, this process goes on continuously through- out all ranges of temperature at which liquid water can exist, and even upon ice at low tem- peratures. It is always accompanied by the conversion of heat, in the^ amount measured by the latent heat of evaporation, into other forms of energy; the heat becomes latent. And since air in contact with water is rarely saturated with aqueous vapor, owing to the constant movement of the atmosphere, the process of evaporation, with the accompany-

ing conversion of heat into latent heat, is a continuous process. The phenomenon is a variable one, however, for while at high tem- perature, both because of the greater supply of heat and because of the greater amount of water vapor that the air can hold, the process is very important and active, at low tem- perature it is far less considerable. This in itself is no doubt a benefit because it tends esJ>eciaUy to restrict the upward march of temperature when the temperature is high, but is of minor importance when the tempera- ture is low.

In view of the other favorable qualities of water it is perhaps not surprising to find that its latent heat of evaporation is by far the highest known. So great, in truth, is this quantity and so important the process that the latent heat of evaporation is one of the mo^ important regulatory factors at present known to meteorologists. When the sun shines upon a body of water, only a small part of the energy which the water receives contributes to the elevation of its temperature. Thus Fitzgerald has con- cluded from his studies of Lough Derg in Ireland during clear hot summer weather ^

* See Harm, "Handbook of Climatology," translated by Ward, p. 131. that in the morning the surface temperature rises about 0.6° per hour. This, however, appears to account for but a small fraction of the solar heat which the lake had taken up; the rest must have been expended in evaporation. Another element of great im- portance is the transparency of water. As a result the rays of the sun are not absorbed by the mere surface alone, but a considerable layer of water near the surface receives the heat.

At the equator the evaporation of the ocean appears to be about 2.3 meters per year/ which involves more than 1,000,000,000,000,- 000 calories of latent heat per square kilo- meter. The amount of heat which is em- ployed in evaporating water from 100 square kilometers of the tropical ocean is accordingly vastly more than all the energy employed in the metabolism of the total population of the United States, and it amounts to more than 100,000,000 horse power. This is equiv- alent to more than one horse power per square meter day and night throughout the year. To a greater or less extent all over the earth this same process goes on, and as a result the water vapor in the air probably averages between 15 and 20 kilograms per square meter of the earth's surface, an ample supply for the formation of rain. The effect of this enormous evaporation to moderate the tem- perature of the tropics is very considerable; but the heat which thus disappears is not lost. Rendered latent at the place of evap- oration, it is turned back into actual heat at

* This and other similar facts will also be found in the work of Hann. the point of condensation, and thus serves to warm another and cooler locality. This process, so vast that all the water power of the globe may be regarded as its secondary by-product, possesses, in respect to its ten- dency to moderate and equalize the temper- ature of ocean, of lakes, and of the climates of all the earth, a maximal value. No other liquid could, during the evaporation of a given quantity of material, bind so much heat; no other vapor could yield so much heat upon condensation.