THE CONDITIONS ESSENTIAL TO EVOLUTION.
§ 100. One more preliminary is needful before proceeding. We have still
to study the conditions under which alone, Evolution can take place.
The process to be interpreted is, as already said, a certain change in
the arrangement of parts. That increase of heterogeneity commonly
displayed throughout Evolution, is not an increase in the number of
kinds of ultimate or undecomposable units which an aggregate contains;
but it is a change in the distribution of such units. If it be assumed
that what we call chemical elements, are absolutely simple (which is,
however, an hypothesis having no better warrant than the opposite one);
then it must be admitted that in respect to the number of kinds of
matter contained in it, the Earth is not more heterogeneous at present
than it was at first—that in this respect, it would be as heterogeneous
were all its undecomposable parts uniformly mixed, as it is now, when
they are arranged and combined in countless different ways. But the
increase of heterogeneity with which we have to deal, and of which alone
our senses can take cognizance, is that produced by the passage from
unity of distribution to variety of distribution. Given an aggregate
consisting of several orders of primitive units that are unchangeable;
then, these units may be so uniformly dispersed among each other, that
any portion of the mass shall be like any other portion in its sensible
properties; or they may be so segregated, simply and in endless
combinations, that the various portions of the mass shall not be like
each other in their sensible properties. A transformation of one of
these arrangements into the other, is that which constitutes Evolution.
We have to analyze the process through which structural uniformity
becomes structural multiformity—to ascertain how the originally equal
relations of position among the mixed units, pass into relations of
position that are more and more unequal, and more and more numerous in
their kinds of inequality; and how this takes place throughout all the
ascending grades of compound units, until we come even to those of which
societies are made up.
Change in the relations of position among the component units, simple or
complex, being the phenomenon we have to interpret; we must first
inquire what are the circumstances which prevent its occurrence, and
what are the circumstances which facilitate it.
* * * * *
§ 101. The constituents of an aggregate cannot be re-arranged, unless
they are moveable: manifestly, they must not be so firmly bound together
that the incident force fails to alter their positions. No bodies are,
indeed, possessed of this absolute rigidity; since an incident force in
being propagated through a body, always produces temporary alterations
in the relative positions of its units, if not permanent alterations. It
is true also, that even permanent re-arrangements of the units may be
thus wrought throughout the interiors of comparatively dense masses,
without any outward sign: as happens with certain crystals, which, on
exposure to sunlight, undergo molecular changes so great as to alter
their planes of cleavage. Nevertheless, since total immobility of the
parts must totally negative their re-arrangement; and since that
comparative immobility which we see in very coherent matter, is a great
obstacle to re-arrangement; it is self-evident that Evolution can be
exhibited in any considerable degree, only where there is comparative
mobility of parts. On the other hand, those definite distributive
changes which constitute Evolution, cannot be extensively or variously
displayed, where the mobility of the parts is extreme. In liquids, the
cohesion of the units is so slight that there is no permanency in their
relations of position to each other. Such re-arrangement as any incident
force generates, is immediately destroyed again by the momentum of the
constituents moved; and so, nothing but that temporary heterogeneity
seen in circulating currents, can be produced. The like still more
obviously holds of gases. Thus, while the theoretical limits
between which Evolution is possible, are absolute immobility of parts
and absolute mobility of parts; we may say that practically, Evolution
cannot go on to any considerable extent where the mobility is very great
or very little. A few examples will facilitate the realization of this
truth.
The highest degrees of Evolution are found in semi-solid bodies, or
bodies that come midway between the two extremes specified. Even
semi-solid bodies of the inorganic class, exhibit the segregation of
mixed units with comparative readiness: witness the fact to which
attention was first drawn by Mr. Babbage, that when the pasty mixture of
ground flints and kaolin, prepared for the manufacture of porcelain, is
kept some time, it becomes gritty and unfit for use, in consequence of
the particles of silica separating themselves from the rest, and uniting
together in grains; or witness the fact known to every housewife, that
in long-kept currant-jelly the sugar takes the shape of imbedded
crystals. While throughout the immense majority of the semi-solid
bodies, namely, the organic bodies, the proclivity to a re-arrangement
of parts is so comparatively great, as to be usually taken for a
distinctive characteristic of them. Among organic bodies
themselves, we may trace contrasts having a like significance. It is an
accepted generalization that, other things equal, the rate of Evolution
is greatest where the plasticity is most marked. In that portion of an
egg which displays the formative processes during the early stages of
incubation, the changes of arrangement are more rapid than those which
an equal portion of the body of a hatched chick undergoes. As may be
inferred from their respective powers to acquire habits and aptitudes,
the structural modifiability of a child is greater than that of an adult
man; and the structural modifiability of an adult man is greater than
that of an old man: contrasts which are accompanied by corresponding
contrasts in the densities of the tissues; since the ratio of water to
solid matter diminishes with advancing age. The most decisive
proof, however, is furnished by those marked retardations or arrests of
organic change, that take place when the tissues suffer a great loss of
water. Certain of the lower animals, as the _Rotifera_, may be rendered
apparently lifeless by desiccation, and will yet revive when wetted: as
their substance passes from the fluid-solid to the solid state, it
ceases to be the seat of those changes which constitute functional
activity and cause structural advance; and such changes recommence as
their substance passes from the solid to the fluid-solid state.
Analogous instances occur among much higher animals. When the African
rivers which it inhabits are dried up, the _Lepidosiren_ remains torpid
in the hardened mud, until the return of the rainy season brings water.
Humboldt states that during the summer drought, the alligators of the
Pampas lie buried in a state of suspended animation beneath the parched
surface, and struggle up out of the earth as soon as it becomes humid.
Now though we have no proof that these partial arrests of vital
activity, are consequent on the reduction of the fluid-solid tissues to
a more solid form; yet their occurrence along with a cessation in the
supply of water, is reason for suspecting that this is the case. And
similarly, though in the more numerous instances where loss of water
leads to complete arrest of vital activity, we are unable to say that
the immediate cause is a stoppage of molecular changes that results from
a diminution of molecular mobility; yet it seems not improbable that
this is the rationale of death by thirst.
Probably few will expect to find this same condition to Evolution,
illustrated in aggregates so widely different in kind as societies. Yet
even here it may be shown that no considerable degree of Evolution is
exhibited, where there is either great mobility of the parts, or great
immobility of them. In such tribes as those inhabiting Australia, we see
extremely little cohesion among the units: there is neither that partial
fixity of relative positions which results from the commencement of
agriculture, nor that partial fixity of relative positions implied by
the establishment of social grades. And along with this want of
cohesion, we find an absence of permanent differentiations. Conversely,
in societies of the oriental type, where accumulated traditions, laws,
and usages, and long-fixed class-arrangements, exercise great
restraining power over individual actions, we find Evolution almost
stopped. Through the medium of institutions and opinions, the forces
brought to bear on each unit by the rest, are so great as to prevent the
units from sensibly yielding to forces tending to re-arrange them. The
condition most favourable to increase of social heterogeneity, is a
medium coherence among the parts—a moderate facility of change in the
relations of citizens, joined with a moderate resistance to such
change—a considerable freedom of individual actions, qualified by a
considerable restraint over individual actions—a certain attachment to
pre-established arrangements, and a certain readiness to be impelled by
new influences into new arrangements—a compromise between fixity and
unfixity such as that which we, perhaps as much as any nation, exhibit.
* * * * *
§ 102. Another condition to Evolution, of the same order as the last
though of a different genus, must be noted. We have found that permanent
re-arrangement among the units of an aggregate, can take place only when
they have neither extreme immobility nor extreme mobility. The mobility
and immobility thus far considered (at least in all aggregates except
social ones) are those due to mechanical cohesion. There is, however,
what we must call chemical cohesion, which also influences the mobility
of the units, and consequently the re-arrangement of them. Manifestly,
if two or more kinds of units contained in any aggregate, are united by
powerful affinities, an incident force, failing to destroy their
cohesions, will not cause such various re-arrangements as it would,
could it produce new chemical combinations as well as new mechanical
adjustments. On the other hand, chemical affinities that are easily
overcome, must be favourable to multiplied re-arrangements of the units.
This condition, as well as the preceding one, is fulfilled in the
highest degree, by those aggregates which most variously display the
transformation of the uniform into the multiform. Organic bodies are on
the average distinguished from inorganic bodies, by the readiness with
which the compounds they consist of undergo decomposition, and
recomposition: the chemical cohesions of their components are so
comparatively small, that small incident forces suffice to overcome them
and cause transpositions of the components. Further, between the two
great divisions of organisms, we find a contrast in the degree of
Evolution co-existing with a contrast in the degree of chemical
modifiability. As a class, the nitrogenous compounds are peculiarly
unstable; and, speaking generally, these are present in much larger
quantities in animal tissues than they are in vegetal tissues; while,
speaking generally, animals are much more heterogeneous than plants.
Under this head it may be well also to point out that, other things
equal, the structural variety which is possible in any aggregate, must
bear a relation to the number of kinds of units contained in the
aggregate. A body made up of units of one order, cannot admit of so many
different re-arrangements, as one made up of units of two orders. And
each additional order of units must increase, in a geometrical
proportion, the number of re-arrangements that may be made.
* * * * *
§ 103. Yet one more condition to be specified, is the state of agitation
in which the constituents of an aggregate are kept. A familiar
expedience will introduce us to this condition. When a vessel has been
filled to the brim with loose fragments, shaking the vessel causes them
to settle down into less space, so that more may be put in. And when
among these fragments, there are some of much greater specific gravity
than the rest, these will, in the course of a prolonged shaking, find
their way to the bottom. What now is the meaning of these two results,
when expressed in general terms? We have a group of units acted on by an
incident force—the attraction of the Earth. So long as these units are
not agitated, this incident force produces no changes in their relative
positions; agitate them, and immediately their loose arrangement passes
into a more compact arrangement. Again, so long as they are not
agitated, the incident force cannot separate the heavier units from the
lighter; agitate them, and immediately the heavier units begin to
segregate. By these illustrations, a rude idea will be conveyed of the
effect which vibration has in facilitating those re-arrangements which
constitute Evolution. What here happens with visible units subject to
visible oscillations, happens also with invisible units subject to
invisible oscillations.
One or two cases in which these oscillations are of mechanical origin,
may first be noted. When a bar of steel is suspended in the magnetic
meridian, and repeatedly so struck as to send vibrations through it, it
becomes magnetized: the magnetic force of the Earth, which does not
permanently affect it while undisturbed, alters its internal state when
a mechanical agitation is propagated among its particles; and the
alteration is believed by physicists, to be a molecular re-arrangement.
It may be fairly objected that this re-arrangement is hypothetical; and
did the fact stand alone, it would be of little worth. It gains
significance, however, when joined with the fact that in the same
substance, long-continued mechanical vibrations are followed by
molecular re-arrangements that are abundantly visible. A piece of iron
which, when it leaves the workshop, is fibrous in structure, will become
crystalline if exposed to a perpetual jar. Though the polar forces
mutually exercised by the atoms, fail to change their disorderly
arrangement into an orderly arrangement while the atoms are relatively
quiescent, these forces produce this change when the atoms are kept in a
state of intestine disturbance.
But the effects which visible oscillations and oscillations sensible to
touch, have in facilitating the re-arrangement of parts by an incident
force, are insignificant compared with the effects which insensible
oscillations have in aiding such change of structure. It is a doctrine
now generally accepted among men of science, that the particles of
tangible matter, as well as the particles of ether, undulate. As
interpreted in conformity with this doctrine, the heat of a body is
simply its state of molecular motion. A mass which feels cold, is one
having but slight molecular motion, and conveying but slight molecular
motion to the surrounding medium or to the hand touching it. A mass hot
enough to radiate a sensible warmth, is one of which the more violently
agitated molecules, communicate increased undulations to the surrounding
ethereal medium; while the burn inflicted by it on the skin, is the
expression of increased undulations of the organic molecules. Such
further heat as produces softening and a consequent distortion of the
mass, is an agitation so much augmented that the units can no longer
completely maintain their relative positions. Fusion is an agitation so
extreme, that the relative positions of the units are changeable with
ease. When, finally, at a still higher temperature, the liquid is
transformed into a gas, the explanation is, that the oscillations are so
violent as to overbalance that force which held the units in close
contiguity—so violent as to keep the units at those relatively great
distances apart to which they are now thrown. Since the
establishment of the correlation between heat and motion first gave
probability to this hypothesis, it has been receiving various
confirmations—especially by recent remarkable discoveries respecting the
absorption of heat by gases. Prof. Tyndall has proved that the quantity
of heat which any gas takes up from rays of heat passing through it, has
a distinct relation to the complexity of the atoms composing the gas.
The simple gases abstract but little; the gases composed of binary atoms
abstract, say in round numbers, a hundred times as much; while the gases
composed of atoms severally containing three, four, or more simple ones,
abstract something like a thousand times as much. These differences
Prof. Tyndall regards as due to the different abilities of the different
atoms to take up, in the increase of their own undulations, those
undulations of the ethereal medium which constitute heat—an
interpretation in perfect accordance with the late results of
spectrum-analysis; which go to show that the various elementary atoms,
when in an aeriform state, intercept those luminiferous vibrations of
the ether which are in unison or harmony with their own. And since it
holds of solid as of gaseous matters, that those consisting of simple
units transmit heat far more readily than those consisting of complex
units; we get confirmation of the inference otherwise reached, that the
units of matter in whatever state of aggregation they exist, oscillate,
and that variations of temperature are variations in the amounts of
their oscillations.
Proceeding on this hypothesis, which it would be out of place here to
defend at greater length, we have now to note how the re-arrangement of
parts is facilitated by these insensible vibrations, as we have seen it
to be by sensible vibrations. One or two cases of physical
re-arrangement may first be noted. When some molten glass is
dropped into water, and when its outside is thus, by sudden
solidification, prevented from partaking in that contraction which the
subsequent cooling of the inside tends to produce; the units are left in
such a state of tension, that the mass flies into fragments if a small
portion of it be broken off. But now, if this mass be kept for a day or
two at a considerable heat, though a heat not sufficient to alter its
form or produce any sensible diminution of hardness, this extreme
brittleness disappears: the component particles being thrown into
greater agitation, the tensile forces are enabled to re-arrange them
into a state of equilibrium. An illustration of another order is
furnished by the subsidence of fine precipitates. These sink down very
slowly from solutions that are cold; while warm solutions deposit them
with comparative rapidity. That is to say, an increase of molecular
vibration throughout the mass, allows the suspended particles to
separate more readily from the particles of fluid. The effect of
heat on chemical re-arrangement is so familiar, that examples are
scarcely needed. Be the substances concerned gaseous, liquid, or solid,
it equally holds that their chemical unions and disunions are aided by a
rise of temperature. Affinities which do not suffice to effect the
re-arrangement of mixed units that are in a state of feeble agitation,
suffice to effect it when the agitation is raised to a certain point.
And so long as this molecular motion is not great enough to prevent
those chemical cohesions which the affinities tend to produce, increase
of it gives increased facility of chemical re-arrangement.
This condition, in common with the preceding ones, is fulfilled most
completely in those aggregates which exhibit the phenomena of Evolution
in the highest degree; namely, the organic aggregates. And throughout
the various orders and states of these, we find minor contrasts showing
the relation between amount of molecular vibration and activity of the
metamorphic changes. Such contrasts may be arranged in the several
following groups. Speaking generally, the phenomena of Evolution
are manifested in a much lower degree throughout the vegetal kingdom
than throughout the animal kingdom; and speaking generally, the heat of
plants is less than that of animals. Among plants themselves, the
organic changes vary in rate as the temperature varies. Though light is
the agent which effects those molecular changes causing vegetal growth,
yet we see that in the absence of heat, such changes are not effected:
in winter there is enough light, but the heat being insufficient,
plant-life is suspended. That this is the sole cause of the suspension,
is proved by the fact that at the same season, plants contained in
hot-houses, where they receive even a smaller amount of light, go on
producing leaves and flowers. A comparison of the several
divisions of the animal kingdom with each other, shows among them
parallel relations. Regarded as a whole, vertebrate animals are higher
in temperature than invertebrate ones; and they are as a whole higher in
organic activity and development. Between subdivisions of the vertebrata
themselves, like differences in the state of molecular vibration,
accompany like differences in the degree of evolution. The least
heterogeneous of the vertebrata are the fishes; and in most cases, the
heat of fishes is nearly the same as that of the water in which they
swim: only some of them being decidedly warmer. Though we habitually
speak of reptiles as cold-blooded; and though they have not much more
power than fishes of maintaining a temperature above that of their
medium; yet since their medium (which is, in the majority of cases, the
air of warm climates) is on the average warmer than the medium inhabited
by fishes, the temperature of the class of reptiles is higher than that
of the class of fishes; and we see in them a correspondingly higher
complexity. The much more active molecular agitation in mammals and
birds, is associated with a considerably greater multiformity of
structure and a very much greater vivacity. And though birds, which are
hotter blooded than mammals, do not show us a greater multiformity; yet,
judging from their apparently greater locomotive powers, we may infer
more rapid functional changes, which, equally with structural changes,
imply molecular re-arrangement. The most instructive contrasts,
however, are those presented by the same organic aggregates at different
temperatures. Thus we see that ova undergoing development, must be kept
more or less warm—that in the absence of a certain molecular vibration,
the re-arrangement of parts does not go on. We see, again, that in
hybernating animals, loss of heat carried to a particular point, results
in extreme retardation of the organic changes. Yet further, we see that
in animals which do not hybernate, as in man, prolonged exposure to
extreme cold, produces an irresistible tendency to sleep (which implies
a lowering of the functional activity); and then, if the abstraction of
heat continues, this sleep ends in death, or arrest of functional
activity. Lastly, we see that when the temperature is lowered till the
contained water solidifies, there is a stoppage not only of those
molecular re-arrangements which constitute life and development, but
also of those molecular re-arrangements which constitute decomposition.
Evidently then, both sensible and insensible agitations among the
components of an aggregate, facilitate any re-distributions to which
there may be a tendency. When that rhythmic change in the relative
positions of the units which constitutes vibration, is considerable, the
relative positions of the units more readily undergo permanent changes
through the action of incident forces.
* * * * *
§ 104. These special conditions to Evolution, are clearly but different
forms of one general condition. The abstract proposition, that a
permanent re-arrangement of units is possible only when they have
neither absolute immobility nor absolute mobility with respect to each
other, we saw to be practically equivalent to the proposition, that
extreme cohesion and extreme want of cohesion among the units are
unfavourable to Evolution. Be this cohesion or want of cohesion that
which physically characterizes the matter as we ordinarily know it; be
it that cohesion or want of cohesion distinguished as chemical; or be it
that cohesion or want of cohesion consequent on the degree of molecular
vibration; matters not, in so far as the general conclusion is
concerned. Inductively as well as deductively, we find that the genesis
of such permanent changes in the relative positions of parts, as can be
effected without destroying the continuity of the aggregate, implies a
medium stability in the relative positions of the parts: be this
stability physical, chemical, or that which varies with the state of
agitation. And as might be anticipated _à priori_, it is proved _à
posteriori_, that this re-arrangement of parts goes on most actively in
those aggregates whose units are moderately influenced by all these
forces which affect their mobility.
Here also may properly be added the remark, that to effect these changes
in the relative positions of parts, the incident forces must range
within certain limits. It is wholly a question of the ratio between
those agencies which hold the units in their positions, and those
agencies which tend to change their positions. Having given intensities
in the powers that oppose re-arrangement, there need proportionate
intensities in the powers that work re-arrangement. As there must be
neither too great nor too little cohesion; so there must be neither too
little nor too great amounts of the influences antagonistic to cohesion.
While a slight mechanical strain produces no lasting alterations in the
relative positions of parts, an excessive mechanical strain causes
disruption—causes so great an alteration in the relative positions of
parts as to destroy their union in one aggregate. While a very feeble
chemical affinity brought to bear on the associated units, fails to work
any re-arrangement of them; a chemical affinity that is extremely
intense, destroys their structural continuity, and reduces such complex
re-arrangements as have been made, to comparatively simple ones. And
while in the absence of adequate thermal undulations, the units have not
freedom enough to obey the re-arranging influences impressed on them,
the incidence of violent thermal undulations gives them such extreme
freedom that they break their connexions, and the aggregate lapses into
a liquid or gaseous form.
On the one hand, therefore, the statical forces which uphold the state
of aggregation must not be so great as wholly to prevent those changes
of relative position among the units which the dynamical forces tend to
produce; and, on the other hand, the dynamical forces must not be so
great as wholly to overcome the statical forces, and destroy the state
of aggregation. The excess of the dynamical forces must be sufficient to
produce Evolution, but not sufficient to produce Dissolution.
* * * * *
§ 105. And now we are naturally introduced to a consideration which,
though it does not come quite within the limits of this chapter as
expressed in its title, may yet be more conveniently dealt with here
than elsewhere. Hitherto we have studied the metamorphosis of things,
only as exhibited in the changed distribution of matter. It remains to
look at it as exhibited in the changed distribution of motion. The
definition of Evolution in its material aspect, has to be supplemented
by a definition of Evolution in its dynamical aspect.
On inquiring the source of the sensible motions seen in every kind of
Evolution, we find them all traceable to insensible motions; either of
that tangible matter which we perceive as constituting the objects
around us, or of that intangible matter which we infer as occupying
space. A brief reconsideration of the facts will make this obvious.
The formation of celestial bodies, supposing it caused by the
union of dispersed units, must, from the beginning, have involved a
diminished motion of these units with respect to each other; and such
motion as each resulting body acquired, must previously have existed in
the motions of its units. If concrete matter has arisen by the
aggregation of diffused matter, then concrete motion has arisen by the
aggregation of diffused motion. That which now exists as the movement of
masses, implies the cessation of an equivalent molecular movement.
Those transpositions of matter which constitute geological
changes, are clearly referable to the same source. As before shown, the
denudation of lands and deposit of new strata, are effected by water in
the course of its descent from the clouds to the sea, or during the
arrest of those undulations produced on it by winds; and, as before
shown, the elevation of water to the height whence it fell, is due to
solar heat, as is also the genesis of those aerial currents which drift
it about when evaporated and agitate its surface when condensed. That is
to say, the molecular motion of the etherial medium, is transformed into
the motion of gases, thence into the motion of liquids, and thence into
the motion of solids—stages in each of which, successively, a certain
amount of molecular motion is lost and an equivalent motion of masses
produced. If we seek the origin of vital movements, we soon reach
a like conclusion. The actinic rays issuing from the Sun, enable the
plant to reduce special elements existing in gaseous combination around
it, to a solid form,—enable the plant, that is, to grow and carry on its
functional changes. And since growth, equally with circulation of sap,
is a mode of sensible motion, while those rays which have been expended
in generating it consist of insensible motions, we have here, too, a
transformation of the kind alleged. Animals, derived as their forces
are, directly or indirectly, from plants, carry this transformation a
step further. The automatic movements of the viscera, together with the
voluntary movements of the limbs and body at large, arise at the expense
of certain molecular movements throughout the nervous and muscular
tissues; and these originally arose at the expense of certain other
molecular movements propagated by the Sun to the Earth; so that both the
structural and functional motions which organic Evolution displays, are
motions of aggregates generated by the arrested motions of units.
Even with the aggregates of these aggregates the same rule holds.
For among associated men, the progress is ever towards a merging of
individual actions in the actions of corporate bodies. An undeveloped
society is composed of members between whom there is little concert:
they fulfil their several wants without mutual aid; and only on
occasions of aggression or defence, act together—occasions on which
their combination, small as it is in extent, frequently fails because it
is so imperfect. In the course of civilization, however, co-operation
becomes step by step more decided. As tribes grow into nations, there
result larger aggregates, each of which has a joint political life—a
common policy and movement with respect to other aggregates. Legislative
and administrative progress, involves an increase in the number of
restraining agents brought into united and simultaneous action. In
military organization, we see an advance from small undisciplined hordes
of armed men, to vast bodies of regular troops, so drilled that the
movements of the units are entirely subordinated to the movements of the
masses. Nor does industrial development fail to show parallel changes.
Beginning with independent workers, and passing step by step to the
employment of several assistants by one master, there has ever been, and
still is, a progress towards the co-operation of greater masses of
labourers in the same establishment, and towards the union of
capitalists into more numerous and larger companies: in both which kinds
of combined action, equivalent amounts of individual action disappear.
Under all its forms, then, Evolution, considered dynamically, is a
decrease in the relative movements of parts, and an increase in the
relative movements of wholes—using the words parts and wholes in their
widest senses. From the infinitesimal motions of those infinitesimal
units composing the etherial medium, to the larger though still
insensible motions of the larger though still insensible units composing
gaseous, fluid, and solid matter, and thence to the visible motions of
visible aggregates, the advance is from molecular motion to the motion
of masses.
But now what of the converse process? If the foregoing proposition is
true, then a change from the motion of masses to molecular motion, is
the opposite to Evolution—is Dissolution. Is this so? Of inorganic
dissolution we have but little experience; or at least, our experience
of it is on too small a scale to exhibit it as the antithesis of
Evolution. We know, indeed, that when solids are dissolved in liquids,
their dissolution implies increased movements of their units, at the
expense of diminished movements among the units of their solvents; and
we know that when a liquid evaporates, its dissipation or dissolution
similarly implies greater relative movements of the units, and decrease
of such combined movement as they before had. But since these small
aggregates of inorganic matter, do not exhibit the phenomena of
Evolution, save in the form of simple integration; so they do not
exhibit the phenomena of dissolution, save in the form of simple
disintegration. Of organic dissolution, however, our experience
suffices to show that it is a decrease of combined motion, and an
increase in the motion of uncombined parts. The gradual cessation of
functions, vegetal or animal, is a cessation of the sensible movements
of fluids and solids. In animals, the impulsions of the body from place
to place, first cease; presently the limbs cannot be stirred; later
still the respiratory actions stop; finally the heart becomes
stationary, and, with it, the circulating fluids. That is, the
transformation of molecular motion into the motion of masses, comes to
an end. What next takes place? We cannot say that sensible movements are
transformed into insensible movements; for sensible movements no longer
exist. Nevertheless, the process of decay involves an increase of
insensible movements; since this is far greater in the gases generated
by decomposition, than it is in the fluid-solid matters generating them.
Indeed, it might be contended that as, during Dissolution, there is a
change from the vibration of large compound atoms to the vibration of
small and comparatively simple ones, the process is strictly
antithetical to that of Evolution. In conformity with the now current
conception lately explained, each of the highly complex chemical units
composing an organic body, possesses a rhythmic movement—a movement in
which its many component units jointly partake. When decomposition
breaks up these highly complex atoms, and their constituents assume a
gaseous form, there is both an increase of molecular motion implied by
the diffusion, and a further increase implied by the resolving of such
motions as the aggregate atoms possessed, into motions of their
constituent atoms. So that in organic dissolution we have, first, an end
put to that transformation of the motion of units into the motion of
aggregates, which constitutes Evolution, dynamically considered; and we
have also, though in a subtler sense, a transformation of the motion of
aggregates into the motion of units. The formula equally applies
to the dissolution of a society. When social ties, be they governmental
or industrial, are destroyed, the combined actions of citizens lapse
into uncombined actions. Those general forces which restrained
individual doings, having disappeared, the only remaining restraints are
those separately exercised by individuals on each other. There are no
longer any of the joint operations by which men satisfy their wants;
and, in so far as they can, they satisfy their wants by separate
operations. That is to say, the movement of parts replaces the movement
of wholes.
Under its dynamical aspect then, Evolution, so far as we can trace it,
is a change from molecular motion to the motion of masses; while
Dissolution, so far as we can trace it, is a change from the motion of
masses to molecular motion.
* * * * *
§ 106. To these abstract definitions may be added concrete ones. Besides
an integration of motions corresponding to the integration of masses,
Evolution involves an increase in the multiformity of the motions,
corresponding to the increase in the multiformity of the masses. If,
contemplating it as materially displayed, we find Evolution to consist
in the change from an indefinite, homogeneous distribution of parts to a
definite, heterogeneous distribution of parts; then, contemplating
Evolution as dynamically displayed, it consists in a change from
indefinite, homogeneous motions to definite, heterogeneous motions.
This change takes place under the form of an increased variety of
rhythms. We have already seen that all motion is rhythmical, from the
infinitesimal vibrations of infinitesimal molecules, up to those vast
oscillations between perihelion and aphelion performed by vast celestial
bodies. And as the contrast between these extreme cases suggests, a
multiplication of rhythms must accompany a multiplication in the degrees
and modes of aggregation, and in the relations of the aggregated masses
to incident forces. The degree or mode of aggregation will not, indeed,
affect the rate or extent of rhythm where the incident force increases
as the aggregate increases, which is the case with gravitation: here the
only cause of variation in rhythm, is difference of relation to the
incident forces; as we see in a pendulum, which, though unaffected in
its movements by a change in the weight of the bob, alters its rate of
oscillation when taken to the equator. But in all cases where the
incident forces do not vary as the masses, every new order of
aggregation initiates a new order of rhythm: witness the conclusion
drawn from the recent researches into radiant heat and light, that the
atoms of different gases have different rates of undulation. So that
increased multiformity in the arrangement of matter, has necessarily
generated increased multiformity of rhythm; both through increased
variety in the sizes and forms of aggregates, and through increased
variety in their relations to the forces which move them. The
advancing heterogeneity of motion, thus entailed by advancing
heterogeneity in the distribution of matter, does not, however, end
here. Besides multiplication in the kinds of rhythm, there is a
progressing complexity in their combinations. As there arise wholes
composed of heterogeneous parts, each of which has its own rhythm, there
must arise compound rhythms proportionately heterogeneous. We before saw
that this is visible even in the cyclical perturbations of the Solar
System—simple as are its structure and movements. And when we
contemplate highly-developed organic bodies, we find the complication of
rhythms so great, that it defies definite analysis, and from moment to
moment works out in resultants that are incalculable.
This conception of Evolution forms a needful complement to that on which
we have hitherto chiefly dwelt. To comprehend the phenomena in their
entirety, we have to contemplate both the increasing multiformity of
parts, and the increasing multiformity of the actions simultaneously
assumed by these parts. At the same time that there are differentiations
and integrations of the matter, there are differentiations and
integrations of its motion. And this increasingly heterogeneous
distribution of motion, constitutes Evolution _functionally_ considered;
as distinguished from that increasingly heterogeneous distribution of
matter, which constitutes Evolution _structurally_ considered. While of
course, Dissolution exhibits the transition to a reverse distribution,
both structurally and functionally.
* * * * *
§ 107. One other preliminary must be set down. When specifically
interpreting Evolution, we shall have to consider under their concrete
forms, the various resolutions of force that follow its conflict with
matter. Here it will be well to contemplate such resolutions under their
most general or abstract forms.
Any incident force is primarily resolvable or divisible into its
_effective_ and _non-effective_ portions. In mechanical impact, the
entire momentum of a striking body is never communicated to the body
struck: even under those most favourable conditions in which the
striking body loses all its sensible motion, there still remains with it
a portion of the original momentum, under the shape of that insensible
motion produced among its particles by the collision. Of the light or
heat falling on any mass, a part, more or less considerable, is
reflected; and only the remaining part works molecular changes in the
mass. Next it is to be noted that the effective force, is itself
divisible into the _temporarily effective_ and the _permanently
effective_. The units of an aggregate acted on, may undergo those
rhythmical changes of relative position which constitute increased
vibration, as well as other changes of relative position which are not
from instant to instant neutralized by opposite ones. Of these, the
first, disappearing in the shape of radiating undulations, leave the
molecular arrangement as it originally was; while the second conduce to
that re-arrangement constituting Evolution. Yet a further
distinction has to be made. The permanently effective force works out
changes of relative position of two kinds—the _insensible_ and the
_sensible_. The insensible transpositions among the units are those
constituting what we call chemical composition and decomposition; and it
is these which we recognize as the qualitative differences that arise in
an aggregate. The sensible transpositions are such as result when
certain of the units, instead of being put into different relations with
their immediate neighbours, are carried away from them and united
together elsewhere.
Concerning these divisions and sub-divisions of any force affecting an
aggregate, the fact which it chiefly concerns us to observe, is, that
they are complementary to each other. Of the whole incident force, the
effective must be that which remains after deducting the non-effective.
The two parts of the effective force must vary inversely as each other:
where much of it is temporarily effective, little of it can be
permanently effective; and _vice versâ_. Lastly, the permanently
effective force, being expended in working both the insensible
re-arrangements which constitute chemical modification, and the sensible
re-arrangements which result in structure, must generate of either kind
an amount that is great or small in proportion as it has generated a
small or great amount of the other.
* * * * *
§ 108. And now of the propositions grouped together in this chapter, it
may be well to remark that, in common with foregoing propositions, they
have for their warrant the fundamental truth with which our synthesis
set out.
That when a given force falls on any aggregate, the permanently
effective part of it will produce an amount of re-arrangement that is
inversely proportional to the cohesion existing among the parts of the
aggregate, is demonstrable _à priori_. Whether the cohesion be
mechanical or chemical, or whether it be temporarily modified by a
changed degree of molecular vibration, matters not to the general
conclusion. In all these cases it follows from the persistence of force,
that in proportion as the units offer great resistance to alteration in
their relative positions, must the amount of motion which a given force
impresses on them be small. The proposition is in fact an identical one;
since the cohesion of units is known to be great or small, only by the
smallness or greatness of the re-arrangement which a given incident
force produces.
The continuity of motion we found to be a corollary from the persistence
of force; and from the continuity of motion, it follows that molecular
motion and the motion of masses can be respectively increased only at
each other’s expense. Hence, if in the course of Evolution there arises
a motion of masses that did not before exist, there must have ceased an
equivalent molecular motion; and if in the course of Dissolution there
arises a molecular motion that did not before exist, an equivalent
motion of masses must have disappeared.
Equally necessary is the conclusion that the several results of the
force expended on any aggregate, must be complementary to each other. It
is not less obviously a corollary from the persistence of force, that of
the whole incident force the effective is the part which remains after
deducting the non-effective; than it is, that of the effective force,
whatever does not work permanent results, works temporary results, and
that such amount of the permanently effective force as is not absorbed
in producing insensible re-arrangements, will produce sensible
re-arrangements.