36
abundant in many rocks, lost 0.075 gramme. The mean of theresults showed that 0.08 gramme was washed in a year from eachsquare metre. Such results give us some indication of the rate atwhich the work of solution goes on in the finely dividedsoils.[1]
It might be urged that, as the mechanical break up of rocks, andthe production in this way of large surfaces, must be at thebasis of solvent and chemical denudation, these latter activitiesshould be predominant in the mountains. The answer to this isthat the soils rarely owe their existence to mechanical actions.The alluvium of the valleys constitutes only narrow margins tothe rivers; the finer _débris_ from the mountains is rapidlybrought into the ocean. The soils which cover the greater part ofcontinental areas have had a very different origin.
In any quarry where a section of the soil and of the underlyingrock is visible, we may study the mode of formation of soils. Ourobservations are, we will suppose, pursued in a granite quarry.We first note that the material of the soil nearest the surfaceis intermixed with the roots of grasses, trees, or shrubs.Examining a handful of this soil, we see glistening flakes ofmica which plainly are derived from the original granite. Washingoff the finer particles, we find the largest remaining grains arecomposed of the all but indestructible quartz.
[1] Proc. Roy. Irish Acad., VIII., Ser. A, p. 21.
37
This also is from the granite. Some few of the grains are ofchalky-looking felspar; again a granitic mineral. What is thefiner silt we have washed off? It, too, is composed of mineralparticles to a great extent; rock dust stained with iron oxideand intermixed with organic remains, both animal and vegetable.But if we make a chemical analysis of the finer silt we find thatthe composition is by no means that of the granite beneath. Thechemist is able to say, from a study of his results, that therehas been, in the first place, a large loss of material attendingthe conversion of the granite to the soil. He finds aconcentration of certain of the more resistant substances of thegranite arising from the loss of the less resistant. Thus thepercentage amount of alumina is increased. The percentage of ironis also increased. But silica and most other substances show adiminished percentage. Notably lime has nearly disappeared. Sodais much reduced; so is magnesia. Potash is not so completelyabstracted. Finally, owing to hydration, there is much morecombined water in the soil than in the rock. This is a typicalresult for rocks of this kind.
Deeper in the soil we often observe a change of texture. It hasbecome finer, and at the same time the clay is paler in colour.This subsoil represents the finer particles carried by rain fromabove. The change of colour is due to the state of the iron whichis less oxidised low down in the soil. Beneath the subsoil thesoil grows
38
again coarser. Finally, we recognise in it fragments of granitewhich ever grow larger as we descend, till the soil has becomereplaced by the loose and shattered rock. Beneath this the onlysign of weathering apparent in the rock is the rusty hue impartedby the oxidised iron which the percolating rain has leached fromiron-bearing minerals.
The soil we have examined has plainly been derived in situ fromthe underlying rock. It represents the more insoluble residueafter water and acids have done their work. Each year there mustbe a very slow sinking of the surface, but the ablation isinfinitesimal.
The depth of such a soil may be considerable. The total surfaceexposed by the countless grains of which it is composed isenormous. In a cubic foot of average soil the surface area of thegrains may be 50,000 square feet or more. Hence a soil only twofeet deep may expose 100,000 square feet for each square foot ofsurface area.
It is true that soils formed in this manner by atmospheric andorganic actions take a very long time to grow. It must beremembered, however, that the process is throughout attended bythe removal in solution: of chemically altered materials.
Considerations such as the foregoing must convince us that whilethe accumulation of the detrital sediments around the continentsis largely the result of activities progressing on the steeperslopes of the land, that is,
39
among the mountainous regions, the feeding of the salts to theocean arises from the slower work of meteorological and organicagencies attacking the molecular constitution of the rocks;processes which best proceed where the drainage is sluggish andthe quiescent conditions permit of the development of abundantorganic growth and decay.
Statistics of the solvent denudation of the continents supportthis view. Within recent years a very large amount of work hasbeen expended on the chemical investigation of river waters ofAmerica and of Europe. F. W. Clarke has, at the expense of muchlabour, collected and compared these results. They are expressedas so many tonnes removed in solution per square mile per annum.For North America the result shows 79 tonnes so removed; forEurope 100 tonnes. Now there is a notable difference between themean elevations of these two continents. North America has a meanelevation of 700 metres over sea level, whereas the meanelevation of Europe is but 300 metres. We see in these figuresthat the more mountainous land supplies less dissolved matter tothe ocean than the land of lower elevation, as our study has ledus to expect.
We have now considered the source of the detrital sediments, aswell as of the dissolved matter which has given to the ocean, inthe course of geological time, its present gigantic load ofsalts. It is true there are further solvent and chemical effectsexerted by the sea water
40
upon the sediments discharged into it; but we are justified inconcluding that, relatively to the similar actions taking placein the soils, the solvent and chemical work of the ocean issmall. The fact is, the deposited detrital sediments around thecontinents occupy an area small when contrasted with the vaststretches of the land. The area of deposition is much less thanthat of denudation; probably hardly as much as one twentieth.And, again, the conditions of aeration and circulation whichlargely promote chemical and solvent denudation in the soils arerelatively limited and ineffective in the detrital oceanicdeposits.
The summation of the amounts of dissolved and detrital materialswhich denudation has brought into the ocean during the longdenudative history of the Earth, as we might anticipate, revealsquantities of almost unrealisable greatness. The facts are amongthe most impressive which geological science has brought tolight. Elsewhere in this volume they have been mentioned whendiscussing the age of the Earth. In the present connection,however, they are deserving of separate consideration.
The basis of our reasoning is that the ocean owes its saltnessmainly if not entirely to the denudative activities we have beenconsidering. We must establish this.
We may, in the first place, say that any other view at onceraises the greatest difficulties. The chemical composition of thedetrital sediments which are spread over
41
the continents and which build up the mountains, differs on theaverage very considerably from that of the igneous rocks. We knowthe former have been derived from the latter, and we know thatthe difference in the composition of the two classes of materialsis due to the removal in solution of certain of the constituentsof the igneous rocks. But the ocean alone can have received thisdissolved matter. We know of no other place in which to look forit. It is true that some part of this dissolved matter has beenagain rejected by the ocean; thus the formation of limestone islargely due to the abstraction of lime from sea water by organicand other agencies. This, however, in no way relieves us of thenecessity of tracing to the ocean the substances dissolved fromthe igneous rocks. It follows that we have here a very causa forthe saltness of the ocean. The view that the ocean "was salt fromthe first" is without one known fact to support it, and leaves uswith the burden of the entire dissolved salts of geological timeto dispose of—Where and how?
The argument we have outlined above becomes convincingly strongwhen examined more closely. For this purpose we first compare theaverage chemical composition of the sedimentary and the igneousrocks. The following table gives the percentages of the chiefchemical constituents: [1]
[1] F. W. Clarke: _A Preliminary Study of Chemical Denudation_,p. 13
42
Igneous. Sedimentary.Silica (SiO2) - 59.99 58.51Alumina (Al2O3) - 15.04 13.07Ferric oxide (F2O3) - 2.59 3.40Ferrous oxide (FeO) - 3.34 2.00Magnesia (MgO) - 3.89 2.52Lime (CaO) - 4.81 5.42Soda (Na2O) - 3.41 1.12Potash (K2O) - 2.95 2.80Water (H2O) - 1.92 4.28Carbon dioxide (CO2) - -- 4.93Minor constituents -2.061.95100.00 100.00
In the derivation of the sediments from the igneous rocks thereis a loss by solution of about 33 per cent; _i.e._ 100 tons ofigneous rock yields rather less than 70 tons of sedimentary rock.This involves a concentration in the sediments of the moreinsoluble constituents. To this rule the lime-content appears tobe an exception. It is not so in reality. Its high value in thesediments is due to its restoration from the ocean to the land.The magnesia and potash are, also, largely restored from theocean; the former in dolomites and magnesian limestones; thelatter in glauconite sands. The iron of the sediments showsincreased oxidation. The most notable difference in the twoanalyses appears, however, in the soda percentages. This fallsfrom 3.41 in the igneous rock to 1.12 in the average sediment.Indeed, this
43
deficiency of soda in sedimentary rocks is so characteristic ofsecondary rocks that it may with some safety be applied todiscriminate between the two classes of substances in cases wherepetrological distinctions of other kinds break down.
To what is this so marked deficiency of soda to be ascribed? Itis a result of the extreme solubility of the salts of sodium inwater. This has not only rendered its deposition by evaporation arelatively rare and unimportant incident of geological history,but also has protected it from abstraction from the ocean byorganic agencies. The element sodium has, in fact, accumulated inthe ocean during the whole of geological time.
We can use the facts associated with the accumulation of sodiumsalts in the ocean as a means of obtaining additional support tothe view, that the processes of solvent denudation areresponsible for the saltness of the ocean. The new evidence maybe stated as follows: Estimates of the amounts of sedimentaryrock on the continents have repeatedly been made. It is true thatthese estimates are no more than approximations. But theyundoubtedly _are_ approximations, and as such may legitimately beused in our argument; more especially as final agreement tends tocheck and to support the several estimates which enter intothem.
The most recent and probable estimates of the sediments on theland assign an average thickness of one mile of
44
secondary rocks over the land area of the world. To this someincrease must be made to allow for similar materials concealed inthe ocean, principally around the continental margins. If we add10 per cent. and assign a specific gravity of 2.5 we get as themass of the sediments 64 x 1016tonnes. But as this is about 67per cent. of the parent igneous rock—_i.e._ the average igneousrock from which the sediments are derived—we conclude that theprimary denuded rock amounted to a mass of about 95 x 1016tonnes.
Now from the mean chemical composition of the secondary rocks wecalculate that the mass of sediments as above determined contains0.72 x1016tonnes of the sodium oxide, Na2O. If to this amount weadd the quantity of sodium oxide which must have been given tothe ocean in order to account for the sodium salts containedtherein, we arrive at a total quantity of oxide of sodium whichmust be that possessed by the primary rock before denudationbegan its work upon it. The mass of the ocean being wellascertained, we easily calculate that the sodium in the oceanconverted to sodium oxide amounts to 2.1 x 1016tonnes. Hencebetween the estimated sediments and the waters of the ocean wecan account for 2.82 x 1016tonnes of soda. When now we put thisquantity back into the estimated mass of primary rock we findthat it assigns to the primary rock a soda percentage of 3.0. Onthe average analysis given above this should be 3.41 per cent.The agreement,
45
all things considered, more especially the uncertainty in theestimate of the sediments, is plainly in support of the view thatoceanic salts are derived from the rocks; if, indeed, it does notrender it a certainty.
A leading and fundamental inference in the denudative history ofthe Earth thus finds support: indeed, we may say, verification.In the light of this fact the whole work of denudation standsrevealed. That the ocean began its history as a vast fresh-waterenvelope of the Globe is a view which accords with the evidencefor the primitive high temperature of the Earth. Geologicalhistory opened with the condensation of an atmosphere of immenseextent, which, after long fluctuations between the states ofsteam and water, finally settled upon the surface, almost free ofmatter in solution: an ocean of distilled water. The epoch ofdenudation then began. It will, probably, continue till thewaters, undergoing further loss of thermal energy, suffer yetanother change of state, when their circulation will cease andtheir attack upon the rocks come to an end.
From what has been reviewed above it is evident that the sodiumin the ocean is an index of the total activity of denudationintegrated over geological time. From this the broad facts of theresults of denudation admit of determination with considerableaccuracy. We can estimate the amount of rock which has beendegraded by solvent and chemical actions, and the amount ofsediments which has been derived from it. We are,
46
thus, able to amend our estimate of the sediments which, asdetermined by direct observation, served to support the basis ofour argument.
We now go straight to the ocean for the amount of sodium ofdenudative origin. There may, indeed, have been some primitivesodium dissolved by a more rapid denudation while the Earth'ssurface was still falling in temperature. It can be shown,however, that this amount was relatively small. Neglecting it wemay say with safety that the quantity of sodium carried into theocean by the rivers must be between 14,000 and 15,000 millionmillion tonnes: _i.e._ 14,500 x 1012tonnes, say.
Keeping the figures to round numbers we find that this amount ofsodium involves the denudation of about 80 x 1016tonnes ofaverage igneous rock to 53 x 1016 tonnes of average sediment.From these vast quantities we know that the parent rock denudedduring geological time amounted to some 300 million cubickilometres or about seventy million cubic miles. The sedimentsderived therefrom possessed a bulk of 220 million cubickilometres or fifty million cubic miles. The area of the landsurface of the Globe is 144 million square kilometres. The parentrock would have covered this to a uniform depth of rather morethan two kilometres, and the derived sediment to more than 1.5kilometres, or about one mile deep.
The slow accomplishment of results so vast conveys some idea ofthe great duration of geological time.
47
The foregoing method of investigating the statistics of solventdenudation is capable of affording information not only as to theamount of sediments upon the land, but also as to the quantitywhich is spread over the floor of the ocean.
We see this when we follow the fate of the 33 per cent. ofdissolved salts which has been leached from the parent igneousrock, and the mass of which we calculate from the ascertainedmass of the latter, to be 27 x 1016tonnes. This quantity was atone time or another all in the ocean. But, as we saw above, acertain part of it has been again abstracted from solution,chiefly by organic agencies. Now the abstracted solids have notbeen altogether retained beneath the ocean. Movements of the landduring geological time have resulted in some portion beinguplifted along with other sediments. These substances constitute,mainly, the limestones.
We see, then, that the 27 x 1016tonnes of substances leachedfrom the parent igneous rocks have had a threefold destination.One part is still in solution; a second part has beenprecipitated to the bottom of the ocean; a third part exists onthe land in the form of calcareous rocks.
Observation on the land sediments shows that the calcareous rocksamount to about 5 per cent. of the whole. From this we find that3 x 1016tonnes, approximately, of such rocks have been takenfrom the ocean. This accounts for one of the three classes ofmaterial
48
into which the original dissolved matter has been divided.Another of the three quantities is easily estimated: the amountof matter still in solution in the ocean. The volume of the oceanis 1,414 million cubic kilometres and its mass is 145 x 1016tonnes. The dissolved salts in it constitute 3.4 per cent. of itsmass; or, rather more than 5 x 1016tonnes. The limestones on theland and the salts in the sea water together make up about 8 x1016tonnes. If we, now, deduct this from the total of 27 x 1016tonnes, we find that about 19 x 1016tonnes must exist asprecipitated matter on the floor of the ocean.
The area of the ocean is 367 x 1012square metres, so that if theprecipitated sediment possesses an average specific gravity of2.5, it would cover the entire floor to a uniform depth of 218metres; that is 715 feet. This assumes that there was uniformdeposition of the abstracted matter over the floor of the ocean.Of course, this assumption is not justifiable. It is certain thatthe rate of deposition on the floor of the sea has variedenormously with various conditions—principally with the depth.Again, it must be remembered that this estimate takes no accountof solid materials otherwise brought into the oceanic deposits;_e.g._, by wind-transported dust from the land or volcanicejectamenta in the ocean depths. It is not probable, however,that any considerable addition to the estimated mean depth ofdeposit from such sources would be allowable.
49
The greatness of the quantities involved in these determinationsis almost awe inspiring. Take the case of the dissolved salts inthe ocean. They are but a fraction, as we have seen, of the totalresults of solvent denudation and represent the integration ofthe minute traces contributed by the river water. Yet the commonsalt (chloride of sodium) alone, contained in the ocean, would,if abstracted and spread over the dry land as a layer of rocksalt having a specific gravity of 2.2, cover the whole to a depthof 107 metres or 354 feet. The total salts in solution in theocean similarly spread over the land would increase the depth ofthe layer to 460 feet. After considering what this means we haveto remember that this amount of matter now in solution in theseas is, in point of fact, less than a fifth part of the totaldissolved from the rocks during geological time.
The transport by denudation of detrital and dissolved matter fromthe land to the ocean has had a most important influence on theevents of geological history. The existing surface features ofthe earth must have been largely conditioned by the dynamicaleffects arising therefrom. In dealing with the subject ofmountain genesis we will, elsewhere, see that all the greatmountain ranges have originated in the accumulation of thedetrital sediments near the shore in areas which, in consequenceof the load, gradually became depressed and developed intosynclines of many thousands of feet in depth. The most impressivesurface features of the Globe originated
50
in this manner. We will see too that these events were of arhythmic character; the upraising of the mountains involvingintensified mechanical denudation over the elevated area and inthis way an accelerated transport of detritus to the sea; theformation of fresh deposits; renewed synclinal sinking of the seafloor, and, finally, the upheaval of a younger mountain range.This extraordinary sequence of events has been determined by theevents of detrital denudation acting along with certain generalconditions which have all along involved the growth ofcompressive stresses in the surface crust of the Earth.
The effects of purely solvent denudation are less easily traced,but, very probably, they have been of not less importance. Irefer here to the transport from the land to the sea of matter insolution.
Solvent denudation, as observed above, takes place mainly in thesoils and in this way over the more level continental areas. Ithas resulted in the removal from the land and transfer to theocean of an amount of matter which represents a uniform layer ofone half a kilometre; that is of more than 1,600 feet of rock.The continents have, during geological time, been lightened tothis extent. On the other hand all this matter has for thegreater part escaped the geosynclines and become uniformlydiffused throughout the ocean or precipitated over its floorprincipally on the continental slopes before the great depths arereached. Of this material the ocean
51
waters contain in solution an amount sufficient to increase theirspecific gravity by 2.7 per cent.
Taking the last point first, it is interesting to note theeffects upon the bulk of the ocean which has resulted from thematter dissolved in it. From the known density of average seawater we find that 100 ccs. of it weigh just 102.7 grammes. Ofthis 3.5 per cent. by weight are solids in solution. That is tosay, 3.594 grammes. Hence the weight of water present is 99.1grammes, or a volume of 99.1 ccs. From this we see that the saltspresent have increased the volume by 0.9 ccs. or 0.9 per cent.
The average depth of the ocean is 2,000 fathoms or 3,700 metres.The increase of depth due to salts dissolved in the ocean hasbeen, therefore, 108 feet or 33.24 metres. This result assumesthat there has been no increased elastic compression due to theincreased pressure, and no change of compressional elasticproperties. We may be sure that the rise on the shore line of theland has not been less than 100 feet.
We see then that as the result of solvent denudation we have todo with a heavier and a deeper ocean, expanded in volume bynearly one per cent. and the floor of which has become raised, onan average, about 700 feet by precipitated sediment.
One of the first conceptions, which the student of geology has todismiss from his mind, is that of the immobility or rigidity ofthe Earth's crust. The lane, we live on sways even to the gentlerise and fail of ocean tides
52
around the coasts. It suffers its own tidal oscillations due tothe moon's attractions. Large tracts of semi-liquid matterunderlie it. There is every evidence that the raised features ofthe Globe are sustained by such pressures acting over other andadjacent areas as serve to keep them in equilibrium against theforce of gravity. This state of equilibrium, which was firstrecognised by Pratt, as part of the dynamics of the Earth'scrust, has been named isostasy. The state of the crust is that of"mobile equilibrium."
The transfer of matter from the exposed land surfaces to thesub-oceanic slopes of the continents and the increase in thedensity of the ocean, must all along have been attended byisostatic readjustment. We cannot take any other view. On the onehand the land was being lightened; on the other the sea wasincreasing in mass and depth and the flanks of the continentswere being loaded with the matter removed from the land and bornein solution to the ocean. How important the resulting movementsmust have been may be gathered from the fact that the existingland of the Globe stands at a mean elevation of no more than2,000 feet above sea level. We have seen that solvent denudationremoved over 1,600 feet of rock. But we have no evidence that onthe whole the elevation of land in the past was ever verydifferent from what it now is.
We have, then, presented to our view the remarkable fact thatthroughout the past, and acting with extreme
53
slowness, the land has steadily been melted down into the sea andas steadily been upraised from the waters. It is possible thatthe increased bulk of the ocean has led to a certain diminutionof the exposed land area. The point is a difficult one. One thingwe may without much risk assume. The sub-aereal current ofdissolved matter from the land to the ocean was accompanied by asub-crustal flux from the ocean areas to the land areas; theheated viscous materials creeping from depths far beneath theocean floor to depths beneath the roots of the mountains whicharose around the oceans. Such movements took ages for theiraccomplishment. Indeed, they have been, probably, continuous allalong and are still proceeding. A low degree of viscosity willsuffice to permit of movements so slow. Superimposed upon thesemovements the rhythmic alternations of depression and elevationof the geosynclines probably resulted in releasing the crust fromlocal accumulation of strains arising in the more rigid surfacematerials. The whole sequence of movements presents anextraordinary picture of pseudo-vitality—reminding us of thecirculatory and respiratory systems of a vast organism.
All great results in our universe are founded in motions andforces the most minute. In contemplating the Cause or the Effectwe stand equally impressed with the spectacle presented to us. Weshall now turn from the great effects of denudation upon thehistory and evolution of a world and consider for a momentactivities
54
so minute in detail that their operations will probably for everelude our bodily senses, but which nevertheless have necessarilyaffected and modified the great results we have beenconsidering.
The ocean a little way from the land is generally so free fromsuspended sediments that it has a blackness as of ink. Thisblackness is due to its absolute freedom from particlesreflecting the sun's light. The beautiful blue of the Swiss andItalian lakes is due to the presence of very fine particlescarried into them by the rivers; the finest flour of theglaciers, which remain almost indefinitely suspended in thewater. But in the ocean it is only in those places where rapidcurrents running over shallows stir continually the sediments orwhere the fresh water of a great river is carried far from theland, that the presence of silt is to be observed. The beautifulphenomenon of the coal-black sea is familiar to every yachtsmanwho has sailed to the west of our Islands.[1]
There is, in fact, a very remarkable difference in the manner ofsettlement of fine sediments in salt and in fresh water. We arehere brought into contact with one of those subtle yetinfluential natural actions the explanation of which involvesscientific advance along many apparently unconnected lines ofinvestigation.
[1] See Tyndall's Voyage to Algeria in _Fragments of Science._ Thecause of the blue colour of the lakes has been discussed byvarious observers, not always with agreement.
55
It is easy to observe in the laboratory the fact of the differentbehaviour of salt and fresh water towards finely dividedsubstances. The nature of the insoluble substance is notimportant.
We place, in a good light, two glass vessels of equal dimensions;the one filled with sea water, the other with fresh water. Intoeach we stir the same weight of very finely powdered slate: justso much as will produce a cloudiness. In a few hours we find thesea water limpid. The fresh water is still cloudy, however; and,indeed, may be hardly different in appearance from what it was atstarting. In itself this is a most extraordinary experiment. Wewould have anticipated quite the opposite result owing to thegreater density of the sea water.
But a still more interesting experiment remains to be carriedout. In the sea water we have many different salts in solution.Let us see if these salts are equally responsible for the resultwe have obtained. For this purpose we measure out quantities ofsodium chloride and magnesium chloride in the proportion in whichthey exist in sea water: that is about as seven to one. We addsuch an equal amount of water to each as represents the dilutionof these salts in sea water. Then finally we stir a little of thefinely powdered slate into each. It will be found that themagnesium chloride, although so much more dilute than the sodiumchloride, is considerably more active in clearing out thesuspension. We may now try such marine salts as magnesiumsulphate,
56
or calcium sulphate against sodium chloride; keeping the marineproportions. Again we find that the magnesium and calcium saltsare the most effective, although so much more dilute than thesodium salt.
There is no visible clue to the explanation of these results. Butwe must conclude as most probable that some action is at work inthe sea water and in the salt solutions which clumps orflocculates the sediment. For only by the gathering of theparticles together in little aggregates can we explain theirrapid fall to the bottom. It is not a question of viscosity(_i.e._ of resistance to the motion of the particles), for thesalt solutions are rather more viscous than the fresh water.Still more remarkable is the fact that every dissolved substancewill not bring about the result. Thus if we dissolve sugar inwater we find that, if anything, the silt settles more slowly inthe sugar solution than in fresh water.
Now there is one effect produced by the solution of such salts aswe have dealt with which is not produced by such bodies as sugar.The water is rendered a conductor of electricity. Long agoFaraday explained this as due to the presence of free atoms ofthe dissolved salt in the solution, carrying electric charges. Wenow speak of the salt as "ionised." That is it is partly split upinto ions or free electrified atoms of chlorine, sodium,magnesium, etc., according to the particular salt in solution.This fact leads us to think that these electrified
57
atoms moving about in the solution may be the cause of theclumping or flocculation. Such electrified atoms are absent fromthe sugar solution: sugar does not become "ionised" when it isdissolved.
The suspicion that the free electrified atoms play a part in thephenomenon is strengthened when we recall the remarkabledifference in the action of sodium chloride and magnesiumchloride. In each of the solutions of these substances there arefree chlorine atoms each of which carries a single charge ofnegative electricity. As these atoms are alike in both solutionsthe different behaviour of the solutions cannot be due to thechlorine. But the metallic atom is very different in the twocases. The ionised sodium atom is known to be _monad_ or carriesbut _one_ positive charge; whereas the magnesium atom is _diad_ andcarries _two_ positive charges. If, then, we assume that themetallic, positively electrified atom is in each caseresponsible, we have something to go on. It may be now statedthat it has been found by experiment and supported by theory thatthe clumping power of an ion rises very rapidly with its valency;that is with the number of unit charges associated with it. Thusdiads such as magnesium, calcium, barium, etc., are very muchmore efficient than monads such as sodium, potassium, etc., andagain, triads such as aluminium are, similarly, very much morepowerful than diad atoms. Here, in short, we have arrived at theactive cause of the phenomenon. Its inner mechanism
58
is, however, harder to fathom. A plausible explanation can beoffered, but a study of it would take us too far. Sufficient hasbeen said to show the very subtile nature of the forces at work.
We have here an effect due to the sea salts derived by denudationfrom the land which has been slowly augmenting during geologicaltime. It is certain that the ocean was practically fresh water inremote ages. During those times the silt from the great riverswould have been carried very far from the land. A Mississippi ofthose ages would have sent its finer suspensions far abroad on acontemporary Gulf stream: not improbably right across theAtlantic. The earlier sediments of argillaceous type were notcollected in the geosynclines and the genesis of the mountainswas delayed proportionately. But it was, probably, not for verylong that such conditions prevailed. For the accumulation ofcalcium salts must have been rapid, and although the greatsalinity due to sodium salts was of slow growth the salts of thediad element calcium must have soon introduced the cooperation ofthe ion in the work of building the mountain.
59
THE ABUNDANCE OF LIFE[1]
WE had reached the Pass of Tre Croci[2]and from a point a littlebelow the summit, looked eastward over the glorious Val Buona.The pines which clothed the floor and lower slopes of the valley,extended their multitudes into the furthest distance, among themany recesses of the mountains, and into the confluent Val diMisurina. In the sunshine the Alpine butterflies flitted fromstone to stone. The ground at our feet and everywhere throughoutthe forests teamed with the countless millions of the small blackants.
It was a magnificent display of vitality; of the aggressivenessof vitality, assailing the barren heights of the limestone,wringing a subsistence from dead things. And the questionsuggested itself with new force: why the abundance of life andits unending activity?
In trying to answer this question, the present sketchoriginated.
I propose to refer for an answer to dynamic considerations. It isapparent that natural selection can only be concerned in asecondary way. Natural selection defines
[1] Proc. Roy. Dublin Soc., vol. vii., 1890.
[2] In the Dolomites of Southeast Tyrol; during the summer of1890. Much of what follows was evolved in discussion with myfellow-traveller, Henry H. Dixon. Much of it is his.
60
a certain course of development for the organism; but veryevidently some property of inherent progressiveness in theorganism must be involved. The mineral is not affected by naturalselection to enter on a course of continual variation andmultiplication. The dynamic relations of the organism with theenvironment are evidently very different from those of inanimatenature.
GENERAL DYNAMIC CONDITIONS ATTENDING INANIMATE ACTIONS
It is necessary, in the first place, to refer briefly to thephenomena attending the transfer of energy within and intoinanimate material systems. It is not assumed here that thesephenomena are restricted in their sphere of action to inanimatenature. It is, in fact, very certain that they are not; but whilethey confer on dead nature its own dynamic tendencies, it willappear that their effects are by various means evaded in livingnature. We, therefore, treat of them as characteristic ofinanimate actions. We accept as fundamental to all theconsiderations which follow the truth of the principle of theConservation of Energy.[1]
[1] "The principle of the Conservation of Energy has acquired somuch scientific weight during the last twenty years that nophysiologist would feel any confidence in an experiment whichshowed a considerable difference between the work done by theanimal and the balance of the account of Energy received andspent."—Clerk Maxwell, _Nature_, vol. xix., p. 142. See alsoHelmholtz _On the Conservation of Force._
61
Whatever speculations may be made as to the course of events verydistant from us in space, it appears certain that dissipation ofenergy is at present actively progressing throughout our sphereof observation in inanimate nature. It follows, in fact, from thesecond law of thermodynamics, that whenever work is derived fromheat, a certain quantity of heat falls in potential without doingwork or, in short, is dissipated. On the other hand, work may beentirely converted into heat. The result is the heat-tendency ofthe universe. Heat, being an undirected form of energy, seeks, asit were, its own level, so that the result of this heat-tendencyis continual approach to uniformity of potential.
The heat-tendency of the universe is also revealed in thefar-reaching "law of maximum work," which defines that chemicalchange, accomplished without the intervention of external energy,tends to the production of the body, or system of bodies, whichdisengage the greatest quantity of heat.[1] And, again, vastnumbers of actions going on throughout nature are attended bydissipatory thermal effects, as those arising from the motions ofproximate molecules (friction, viscosity), and from the fall ofelectrical potential.
Thus, on all sides, the energy which was once most probablyexistent in the form of gravitational potential, is beingdissipated into unavailable forms. We must
[1] Berthelot, _Essai de Mécanique Chimique._
62
recognize dissipation as an inevitable attendant on inanimatetransfer of energy.
But when we come to consider inanimate actions in relation totime, or time-rate of change, we find a new feature in thephenomena attending transfer of energy; a feature which is reallyinvolved in general statements as to the laws of physicalinteractions.[1] It is seen, that the attitude of inanimatematerial systems is very generally, if not in all cases,retardative of change—opposing it by effects generated by theprimary action, which may be called "secondary" for convenience.Further, it will be seen that these secondary effects are thoseconcerned in bringing about the inevitable dissipation.
As example, let us endeavour to transfer gravitational potentialenergy contained in a mass raised above the surface of the Earthinto an elastic body, which we can put into compression byresting the weight upon it. In this way work is done againstelastic force and stored as elastic potential energy. We may dealwith a metal spring, or with a mass of gas contained in acylinder fitted with a piston upon which the weight may beplaced. In either case we find the effect of compression is toraise the temperature of the substance, thus causing its
[1] Helmholtz, _Ice and Glaciers._ Atkinson's collection of hisPopular Lectures. First Series, p.120. Quoted by Tate, _Heat_,p. 311.
63
expansion or increased resistance to the descent of the weight.And this resistance continues, with diminishing intensity, tillall the heat generated is dissipated into the surrounding medium.The secondary effect thus delays the final transfer of energy.
Again, if we suppose the gas in the cylinder replaced by a vapourin a state of saturation, the effect of increased pressure, as ofa weight placed upon the piston, is to reduce the vapour to aliquid, thereby bringing about a great diminution of volume andproportional loss of gravitational potential by the weight. Butthis change will by no means be brought about instantaneously.When a little of the vapour is condensed, this portion parts withlatent heat of vaporisation, increasing the tension of theremainder, or raising its point of saturation, so that before theweight descends any further, this heat has to escape from thecylinder.
Many more such cases might be cited. The heating of india-rubberwhen expanded, its cooling when compressed, is a remarkable one;for at first sight it appears as if this must render itexceptional to the general law, most substances exhibiting theopposite thermal effects when stressed. However, here, too, theaction of the stress is opposed by the secondary effectsdeveloped in the substance; for it is found that this substancecontracts when heated, expands when cooled. Again, ice being asubstance which contracts in melting, the effect of pressure isto facilitate melting, lowering its freezing point. But
64
so soon as a little melting occurs, the resulting liquid calls onthe residual ice for an amount of heat equivalent to the latentheat of liquefaction, and so by cooling the whole, retards thechange.
Such particular cases illustrate a principle controlling theinteraction of matter and energy which seems universal inapplication save when evaded, as we shall see, by the ingenuityof life. This principle is not only revealed in the researches ofthe laboratory; it is manifest in the history of worlds and solarsystems. Thus, consider the effects arising from the aggregationof matter in space under the influence of the mutual attractionof the particles. The tendency here is loss of gravitationalpotential. The final approach is however retarded by thetemperature, or vis viva of the parts attending collision andcompression. From this cause the great suns of space radiate forages before the final loss of potential is attained.
Clerk Maxwell[1] observes on the general principle that lessforce is required to produce a change in a body when the changeis unopposed by constraints than when it is subjected to such.From this if we assume the external forces acting upon a systemnot to rise above a certain potential (which is the order ofnature), the constraints of secondary actions may, under certaincircumstances, lead to final rejection of some of the energy, or,in any
[1] _Theory of Heat_, p. 131.
65
case, to retardation of change in the system—dissipation ofenergy being the result.[1]
As such constraints seem inherently present in the properties ofmatter, we may summarise as follows:
_The transfer of energy into any inanimate material system isattended by effects retardative to the transfer and conducive todissipation._
Was this the only possible dynamic order ruling in materialsystems it is quite certain the myriads of ants and pines nevercould have been, except all generated by creative act at vastprimary expenditure of energy. Growth and reproduction would havebeen impossible in systems which retarded change at every stepand never proceeded in any direction but in that of dissipation.Once created, indeed, it is conceivable that, as heat engines,they might have dragged out an existence of alternate life anddeath; life in the hours of sunshine, death in hours of darkness:no final death, however, their lot, till their parts were simplyworn out by long use, never made good by repair. But thesustained and increasing activity of organized nature is a fact;therefore some other order of events must be possible.
[1] The law of Least Action, which has been applied, not alone inoptics, but in many mechanical systems, appears physically basedupon the restraint and retardation opposing the transfer ofenergy in material systems.
66
GENERAL DYNAMIC CONDITIONS ATTENDING ANIMATE ACTIONS
What is the actual dynamic attitude of the primary organicengine—the vegetable organism? We consider, here, in the firstplace, not intervening, but resulting phenomena.
The young leaf exposed to solar radiation is small at first, andthe quantity of radiant energy it receives in unit of time cannotexceed that which falls upon its surface. But what is the effectof this energy? Not to produce a retardative reaction, but anaccelerative response: for, in the enlarging of the leaf bygrowth, the plant opens for itself new channels of supply.
If we refer to "the living protoplasm which, with its unknownmolecular arrangement, is the only absolute test of the cell andof the organism in general,[1] we find a similar attitude towardsexternal sources of available energy. In the act of growthincreased rate of assimilation is involved, so that there is anacceleration of change till a bulk of maximum activity isattained. The surface, finally, becomes too small for theabsorption of energy adequate to sustain further increase of mass(Spencer[2]), and the acceleration ceases. The waste going on inthe central parts is then just balanced by the renewal at thesurface. By division, by spreading of the mass, by
[1] Claus, _Zoology_, p. 13.
[2] Geddes and Thomson, _The Evolution of Sex_, p. 220.
67
out-flowing processes, the normal activity of growth may berestored. Till this moment nothing would be gained by any ofthese changes. One or other of them is now conducive toprogressive absorption of energy by the organism, and one orother occurs, most generally the best of them, subdivision. Twounits now exist; the total mass immediately on division isunaltered, but paths for the more abundant absorption of energyare laid open.
The encystment of the protoplasm (occurring under conditions uponwhich naturalists do not seem agreed[1]) is to all appearanceprotective from an unfavourable environment, but it is often aperiod of internal change as well, resulting in a segregationwithin the mass of numerous small units, followed by a breakup ofthe whole into these units. It is thus an extension of the basisof supply, and in an impoverished medium, where unit of surfaceis less active, is evidently the best means of preserving acondition of progress.
Thus, in the organism which forms the basis of all modes of life,a definite law of action is obeyed under various circumstances ofreaction with the available energy of its environment.
Similarly, in the case of the more complex leaf, we see, not onlyin the phenomenon of growth, but in its extension in a flattenedform, and in the orientation of greatest surface towards thesource of energy, an attitude towards
[1] However, "In no way comparable with death." Weismann,_Biological Memoirs_, p. 158.
68
available energy causative of accelerated transfer. There isseemingly a principle at work, leading to the increase of organicactivity.
Many other examples might be adduced. The gastrula stage in thedevelopment of embryos, where by invagination such an arrangementof the multiplying cells is secured as to offer the greatestpossible surface consistent with a first division of labour; theprovision of cilia for drawing upon the energy supplies of themedium; and more generally the specialisation of organs in thehigher developments of life, may alike be regarded as efforts ofthe organism directed to the absorption of energy. When anyparticular organ becomes unavailing in the obtainment ofsupplies, the organ in the course of time becomes aborted ordisappears.[1] On the other hand, when a too ready and liberalsupply renders exertion and specialisation unnecessary, a similarabortion of functionless organs takes place. This is seen in thedegraded members of certain parasites.
During certain epochs of geological history, the vegetable worlddeveloped enormously; in response probably to liberal supplies ofcarbon dioxide. A structural adaptation to the rich atmosphereoccurred, such as was calculated to cooperate in rapidlyconsuming the supplies, and to this obedience to a law ofprogressive transfer of energy we owe the vast stores of energynow accumulated
[1] Claus, _Zoology_, p. 157
69
in our coal fields. And when, further, we reflect that this storeof energy had long since been dissipated into space but for theintervention of the organism, we see definitely another factor inorganic transfer of energy—a factor acting conservatively ofenergy, or antagonistically to dissipation.
The tendency of organized nature in the presence of unlimitedsupplies is to "run riot." This seems so universal a relation,that we are safe in seeing here cause and effect, and in drawingour conclusions as to the attitude of the organism towardsavailable energy. New species, when they come on the field ofgeological history, armed with fresh adaptations, irresistibletill the slow defences of the subjected organisms are completed,attain enormous sizes under the stimulus of abundant supply, tillfinally, the environment, living and dead, reacts upon them withrestraining influence. The exuberance of the organism in presenceof energy is often so abundant as to lead by deprivation to itsself-destruction. Thus the growth of bacteria is often controlledby their own waste products. A moment's consideration shows thatsuch progressive activity denotes an accelerative attitude on thepart of the organism towards the transfer of energy into theorganic material system. Finally, we are conscious in ourselveshow, by use, our faculties are developed; and it is apparent thatall such progressive developments must rest on actions whichrespond to supplies with fresh demands. Possibly in the presentand ever-
70
increasing consumption of inanimate power by civilised races, wesee revealed the dynamic attitude of the organism working throughthought-processes.
Whether this be so or not, we find generally in organised naturecauses at work which in some way lead to a progressive transferof energy into the organic system. And we notice, too, that allis not spent, but both immediately in the growth of theindividual, and ultimately in the multiplication of the species,there are actions associated with vitality which retard thedissipation of energy. We proceed to state the dynamicalprinciples involved in these manifestations, which appearcharacteristic of the organism, as follows:—
_The transfer of energy into any animate material system isattended by effects conducive to the transfer, and retardative ofdissipation._
This statement is, I think, perfectly general. It has been inpart advanced before, but from the organic more than the physicalpoint of view. Thus, "hunger is an essential characteristic ofliving matter"; and again, "hunger is a dominant characteristicof living matter,"[1] are, in part, expressions of the statement.If it be objected against the generality of the statement, thatthere are periods in the life of individuals when stagnation anddecay make their appearance, we may answer, that
[1] _Evolution of Sex._ Geddes and Thomson, chap. xvi. See also areference to Cope's theory of "Growth Force," in Wallace's_Darwinism_, p. 425.
71
such phenomena arise in phases of life developed under conditionsof external constraint, as will be urged more fully further on,and that in fact the special conditions of old age do not andcannot express the true law and tendency of the dynamic relationsof life in the face of its evident advance upon the Earth. Thelaw of the unconstrained cell is growth on an ever increasingscale; and although we assume the organic configuration, whethersomatic or reproductive, to be essentially unstable, so thatcontinual inflow of energy is required merely to keep it inexistence, this does not vitiate the fact that, when free of allexternal constraint, growth gains on waste. Indeed, even in thecase of old age, the statement remains essentially true, for thephenomena then displayed point to a breakdown of the functioningpower of the cell, an approximation to configurations incapableof assimilation. It is not as if life showed in these phenomenathat its conditions could obtain in the midst of abundance, andyet its law be suspended; but as if they represented adegradation of the very conditions of life, a break up, under thelaws of the inanimate, of the animate contrivance; so that energyis no longer available to it, or the primary condition, "thetransfer of energy into the animate system," is imperfectlyobeyed. It is to the perfect contrivance of life our statementrefers.
That the final end of all will be general non-availability thereseems little reason to doubt, and the organism, itself dependentupon differences of potential, cannot
72
hope to carry on aggregation of energy beyond the period whendifferences of potential are not. The organism is not accountablefor this. It is being affected by events external to it, by theactions going on through inanimate agents. And although there beonly a part of the received energy preserved, there is a partpreserved, and this amount is continually on the increase. To seethis it is only necessary to reflect that the sum of animateenergy—capability of doing work in any way through animatemeans—at present upon the Earth, is the result, although a smallone, of energy reaching the Earth since a remote period, andwhich otherwise had been dissipated in space. In inanimateactions throughout nature, as we know it, the availability iscontinually diminishing. The change is all the one way. As,however, the supply of available energy in the universe is(probably) limited in amount, we must look upon the two as simplyeffecting the final dissipation of potential in very differentways. The animate system is aggressive on the energy available toit, spends with economy, and invests at interest till deathfinally deprives it of all. It has heirs, indeed, who inheritsome of its gains, but they, too, must die, and ultimately therewill be no successors, and the greater part must melt away as ifit had never been. The inanimate system responds to the forcesimposed upon it by sluggish changes; of that which is thrust uponit, it squanders uselessly. The path of the energy is verydifferent in the two cases.
73
While it is true generally that both systems ultimately result inthe dissipation of energy to uniform potential, the organism can,as we have seen, under particular circumstances evade the finaldoom altogether. It can lay up a store of potential energy whichmay be permanent. Thus, so long as there is free oxygen in theuniverse, our coalfields might, at any time in the remote future,generate light and heat in the universal grave.
It is necessary to observe on the fundamental distinction betweenthe growth of the protoplasm and the growth of the crystal. It iscommon to draw comparison between the two, and to point tometabolism as the chief distinction. But while this is the mostobvious distinction the more fundamental one remains in theenergy relations of the two with the environment.[1] The growthof the crystal is the result of loss of energy; that of theorganism the result of gain of energy. The crystal represents alast position of stable equilibrium assumed by molecules upon acertain loss of kinetic energy, and the formation of the crystalby evaporation and concentration of a liquid does not, in itsdynamic aspect, differ much from the precipitation of anamorphous sediment. The organism, on the other hand, represents amore or less unstable condition formed and maintained by inflowof energy; its formation, indeed, often attended with a loss ofkinetic energy (fixation of carbon in plants), but, if so,accompanied by
[1] It appears exceptional for the crystal line configuration tostand higher in the scale of energy than the amorphous.
74
a more than compensatory increase of potential molecular energy.
Thus, between growth in the living world and growth in the deadworld, the energy relations with the environment reveal a markedcontrast. Again, in the phenomena of combustion, there arecertain superficial resemblances which have led to comparisonbetween the two. Here again, however, the attitudes towards theenergy of the environment stand very much as + and -. The lifeabsorbs, stores, and spends with economy. The flame onlyrecklessly spends. The property of storage by the organism callsout a further distinction between the course of the twoprocesses. It secures that the chemical activity of the organismcan be propagated in a medium in which the supply of energy isdiscontinuous or localised. The chemical activity of thecombustion can, strictly speaking, only be propagated amongcontiguous particles. I need not dwell on the latter fact; anexample of the former is seen in the action of the roots ofplants, which will often traverse a barren place or circumvent anobstacle in their search for energy. In this manner roots willfind out spots of rich nutriment.
Thus there is a dynamic distinction between the progress of theorganism and the progress of the combustion, or of the chemicalreaction generally. And although there be unstable chemicalsystems which absorb energy during reaction, these are(dynamically) no more than the expansion of the compressed gas.There is a certain
75
initial capacity in the system for a given quantity of energy;this satisfied, progress ceases. The progress of the organism intime is continual, and goes on from less to greater so long asits development is unconstrained and the supply of energy isunlimited.
We must regard the organism as a configuration which is socontrived as to evade the tendency of the universal laws ofnature. Except we are prepared to believe that a violation of thesecond law of thermodynamics occurs in the organism, that a"sorting demon" is at work within it, we must, I think, assumethat the interactions going on among its molecules areaccompanied by retardation and dissipation like the rest ofnature. That such conditions are not incompatible with thedefinition of the dynamic attitude of the organism, can be shownby analogy with our inanimate machines which, by aid ofhypotheses in keeping with the second law of thermodynamics, maybe supposed to fulfil the energy-functions of the plant oranimal, and, in fact, in all apparent respects conform to thedefinition of the organism.
We may assume this accomplished by a contrivance of the nature ofa steam-engine, driven by solar energy. It has a boiler, which wemay suppose fed by the action of the engine. It has piston,cranks, and other movable parts, all subject to resistance fromfriction, etc. Now there is no reason why this engine should notexpend its surplus energy in shaping, fitting, and starting intoaction other engines:—in fact, in reproductive sacrifice. All
76
these other engines represent a multiplied absorption of energyas the effects of the energy received by the parent engine, andmay in time be supposed to reproduce themselves. Further, we maysuppose the parent engine to be small and capable of developingvery little power, but the whole series as increasing in power ateach generation. Thus the primary energy relations of thevegetable organism are represented in these engines, and noviolation of the second law of thermodynamics involved.
We might extend the analogy, and assuming these engines to spenda portion of their surplus energy in doing work against chemicalforces—as, for example, by decomposing water through theintervention of a dynamo—suppose them to lay up in this way astore of potential energy capable of heating the boilers of asecond order of engines, representing the graminivorous animal.It is obvious without proceeding to a tertiary or carnivorousorder, that the condition of energy in the animal world may besupposed fulfilled in these successive series of engines, and noviolation of the principles governing the actions going on in ourmachines assumed. Organisms evolving on similar principles wouldexperience loss at every transfer. Thus only a portion of theradiant energy absorbed by the leaf would be expended in actualwork, chemical and gravitational, etc. It is very certain thatthis is, in fact, what takes place.
It is, perhaps, worth passing observation that, from thenutritive dependence of the animal upon the vegetable,
77
and the fact that a conversion of the energy of the one to thepurposes of the other cannot occur without loss, the mean energyabsorbed daily by the vegetable for the purpose of growth mustgreatly exceed that used in animal growth; so that the chemicalpotential energy of vegetation upon the earth is much greaterthan the energy of all kinds represented in the animalconfigurations.[1] It appears, too, that in the power possessedby the vegetable of remaining comparatively inactive, ofsurviving hard times by the expenditure and absorption of butlittle, the vegetable constitutes a veritable reservoir for theuniform supply of the more unstable and active animal.
Finally, on the question of the manner of origin of organicsystems, it is to be observed that, while the life of the presentis very surely the survival of the fittest of the tendencies andchances of the past, yet, in the initiation of the organisedworld, a single chance may have decided a whole course of events:for, once originated, its own law secures its increase, althoughwithin the new order of actions, the law of the fittest mustassert itself. That such a progressive material system as anorganism was possible, and at some remote period was initiated,is matter of knowledge; whether or not the initiatory livingconfiguration was rare and fortuitous, or the probable result ofthe general action of physical laws acting among innumerablechances, must remain matter of
[1] I find a similar conclusion arrived at in Semper's _AnimalLife_, p. 52.
78
speculation. In the event of the former being the truth, it isevidently possible, in spite of a large finite number ofhabitable worlds, that life is non-existent elsewhere. If thelatter is the truth, it is almost certain that there is life inall, or many of those worlds.
EVOLUTION AND ACCELERATION OF ACTIVITY
The primary factor in evolution is the "struggle for existence."This involves a "natural selection" among the many variations ofthe organism. If we seek the underlying causes of the struggle,we find that the necessity of food and (in a lesser degree) thedesire for a mate are the principal causes of contention. Theformer is much the more important factor, and, accordingly, wefind the greater degree of specialisation based upon it.
The present view assumes a dynamic necessity for its demandsinvolved in the nature of the organism as such. This assumptionis based on observation of the outcome of its unconstrainedgrowth, reproduction, and life-acts. We have the same right toassert this of the organism as we have to assert that retardationand degradation attend the actions of inanimate machines, whichassertion, also, is based on observation of results. Thus we passfrom the superficial statements that organisms require food inorder to live, or that organisms desire food, to the morefundamental one that:
_The organism is a configuration of matter which absorbs energyacceleratively, without limit, when unconstrained._
79
This is the dynamic basis for a "struggle for existence." Theorganism being a material system responding to accession ofenergy with fresh demands, and energy being limited in amount,the struggle follows as a necessity. Thus, evolution guiding' thesteps of the energy-seeking organism, must presuppose and findits origin in that inherent property of the organism whichdetermines its attitude in presence of available energy.
Turning to the factor, "adaptation," we find that this also mustpresuppose, in order to be explicable, some quality ofaggressiveness on the part of the organism. For adaptation inthis or that direction is the result of repulse or victory, and,therefore, we must presuppose an attack. The attack is made bythe organism in obedience to its law of demand; we see in theadaptation of the organism but the accumulated wisdom derivedfrom past defeats and victories.
Where the environment is active, that is living, adaptationoccurs on both sides. Improved means of defence or improved meansof attack, both presuppose activity. Thus the reactions to theenvironment, animate and inanimate, are at once the outcome ofthe eternal aggressiveness of the organism, and the source offresh aggressiveness upon the resources of the medium.
As concerns the "survival of the fittest" (or "naturalselection"), we can, I think, at once conclude that the organismwhich best fulfils the organic law under the circumstances ofsupply is the "fittest," _ipso facto._ In many
80
cases this is contained in the commonsense consideration, that tobe strong, consistent with concealment from enemies which arestronger, is best, as giving the organism mastery over foes whichare weaker, and generally renders it better able to securesupplies. Weismann points out that natural selection favoursearly and abundant reproduction. But whether the qualificationsof the "fittest" be strength, fertility, cunning, fleetness,imitation, or concealment, we are safe in concluding that growthand reproduction must be the primary qualities which at oncedetermine selection and are fostered by it. Inherent in thenature of the organism is accelerated absorption of energy, butthe qualifications of the "fittest" are various, for the supplyof energy is limited, and there are many competitors for it. Tosecure that none be wasted is ultimately the object of naturalselection, deciding among the eager competitors what is best foreach.
In short, the facts and generalisations concerning evolution mustpresuppose an organism endowed with the quality of progressiveabsorption of energy, and retentive of it. The continuity oforganic activity in a world where supplies are intermittent isevidently only possible upon the latter condition. Thus itappears that the dynamic attitude of the organism, considered inthese pages, occupies a fundamental position regarding itsevolution.
We turn to the consideration of old age and death, endeavouringto discover in what relation they stand to the innateprogressiveness of the organism.
81
THE PERIODICITY OF THE ORGANISM AND THE LAW OF PROGRESSIVEACTIVITY
The organic system is essentially unstable. Its aggressiveattitude is involved in the phenomenon of growth, and inreproduction which is a form of growth. But the energy absorbedis not only spent in growth. It partly goes, also, to make goodthe decay which arises from the instability of the organic unit.The cell is molecularly perishable. It possesses its entity muchas a top keeps erect, by the continual inflow of energy.Metabolism is always taking place within it. Any other conditionwould, probably, involve the difficulties of perpetual motion.
The phenomenon of old age is not evident in the case of theunicellular organism reproducing by fission. At any stage of itshistory all the individuals are of the same age: all contain alike portion of the original cell, so far as this can be regardedas persisting where there is continual flux of matter and energy.In the higher organisms death is universally evident. Why isthis?
The question is one of great complexity. Considered from the morefundamental molecular point of view we should perhaps look tofailure of the power of cell division as the condition ofmortality. For it is to this phenomenon—that of celldivision—that the continued life of the protozoon is to beascribed, as we have already seen. Reproduction is, in fact, thesaving factor here.