THE INSTABILITY OF THE HOMOGENEOUS.[16]
§ 109. Thus far our steps towards the interpretation of Evolution have
been preparatory. We have dealt with the factors of the process, rather
than the process itself. After the ultimate truth that, Matter, Motion,
and Force, as cognizable by human intelligence, can neither come into
existence nor cease to exist, we have considered certain other ultimate
truths concerning the modes in which Force and Motion are manifested
during the changes they produce in Matter. Now we have to study the
changes themselves. We have here to analyze that re-arrangement in the
parts of Matter, which occurs under the influence of Force, that is
unchangeable in quantity though changeable in form, through the medium
of Motion taking place rhythmically along lines of least resistance. The
proposition which comes first in logical order, is, that some
re-arrangement must result; and this proposition may be best dealt with
under the more specific shape, that the condition of homogeneity is a
condition of unstable equilibrium.
First, as to the meaning of the terms; respecting which some readers may
need explanation. The phrase _unstable equilibrium_ is one used in
mechanics to express a balance of forces of such kind, that the
interference of any further force, however minute, will destroy the
arrangement previously subsisting; and bring about a totally different
arrangement. Thus, a stick poised on its lower end is in unstable
equilibrium: however exactly it may be placed in a perpendicular
position, as soon as it is left to itself it begins, at first
imperceptibly, to lean on one side, and with increasing rapidity falls
into another attitude. Conversely, a stick suspended from its upper end
is in stable equilibrium: however much disturbed, it will return to the
same position. The proposition is, then, that the state of homogeneity,
like the state of the stick poised on its lower end, is one that cannot
be maintained. Let us take a few illustrations.
Of mechanical ones the most familiar is that of the scales. If they be
accurately made, and not clogged by dirt or rust, it is impossible to
keep a pair of scales perfectly balanced: eventually one scale will
descend and the other ascend—they will assume a heterogeneous relation.
Again, if we sprinkle over the surface of a fluid a number of
equal-sized particles, having an attraction for each other, they will,
no matter how uniformly distributed, by and by concentrate irregularly
into one or more groups. Were it possible to bring a mass of water into
a state of perfect homogeneity—a state of complete quiescence, and
exactly equal density throughout—yet the radiation of heat from
neighbouring bodies, by affecting differently its different parts, would
inevitably produce inequalities of density and consequent currents; and
would so render it to that extent heterogeneous. Take a piece of red-hot
matter, and however evenly heated it may at first be, it will quickly
cease to be so: the exterior, cooling faster than the interior, will
become different in temperature from it. And the lapse into
heterogeneity of temperature, so obvious in this extreme case, takes
place more or less in all cases. The action of chemical forces
supplies other illustrations. Expose a fragment of metal to air or
water, and in course of time it will be coated with a film of oxide,
carbonate, or other compound: that is—its outer parts will become unlike
its inner parts. Usually the heterogeneity produced by the action of
chemical forces on the surfaces of masses, is not striking; because the
changed portions are soon washed away, or otherwise removed. But if this
is prevented, comparatively complex structures result. Quarries of
trap-rock contain some striking examples. Not unfrequently a piece of
trap may be found reduced, by the action of the weather, to a number of
loosely-adherent coats, like those of an onion. Where the block has been
quite undisturbed, we may trace the whole series of these, from the
angular, irregular outer one, through successively included ones in
which the shape becomes gradually rounded, ending finally in a spherical
nucleus. On comparing the original mass of stone with this group of
concentric coats, each of which differs from the rest in form, and
probably in the state of decomposition at which it has arrived, we get a
marked illustration of the multiformity to which, in lapse of time, a
uniform body may be brought by external chemical action. The
instability of the homogeneous is equally seen in the changes set up
throughout the interior of a mass, when it consists of units that are
not rigidly bound together. The atoms of a precipitate never remain
separate, and equably distributed through the fluid in which they make
their appearance. They aggregate either into crystalline grains, each
containing an immense number of atoms, or they aggregate into flocculi,
each containing a yet larger number; and where the mass of fluid is
great, and the process prolonged, these flocculi do not continue
equidistant, but break up into groups. That is to say, there is a
destruction of the balance at first subsisting among the diffused
particles, and also of the balance at first subsisting among the groups
into which these particles unite. Certain solutions of
non-crystalline substances in highly volatile liquids, exhibit in the
course of half an hour a whole series of changes that are set up in the
alleged way. If for example a little shell-lac-varnish (made by
dissolving shell-lac in coal-naphtha until it is of the consistence of
cream) be poured on a piece of paper, the surface of the varnish will
shortly become marked by polygonal divisions, which, first appearing
round the edge of the mass, spread towards its centre. Under a lense
these irregular polygons of five or more sides, are seen to be severally
bounded by dark lines, on each side of which there are light-coloured
borders. By the addition of matter to their inner edges, the borders
slowly broaden, and thus encroach on the areas of the polygons; until at
length there remains nothing but a dark spot in the centre of each. At
the same time the boundaries of the polygons become curved; and they end
by appearing like spherical sacs pressed together; strangely simulating
(but only simulating) a group of nucleated cells. Here a rapid loss of
homogeneity is exhibited in three ways:—First, in the formation of the
film, which is the seat of these changes; second, in the formation of
the polygonal sections into which this film divides; and third, in the
contrast that arises between the polygonal sections round the edge,
where they are small and early formed, and those in the centre which are
larger and formed later.
The instability thus variously illustrated is obviously consequent on
the fact, that the several parts of any homogeneous aggregation are
necessarily exposed to different forces—forces that differ either in
kind or amount; and being exposed to different forces they are of
necessity differently modified. The relations of outside and inside, and
of comparative nearness to neighbouring sources of influence, imply the
reception of influences that are unlike in quantity or quality, or both;
and it follows that unlike changes will be produced in the parts thus
dissimilarly acted upon.
For like reasons it is manifest that the process must repeat itself in
each of the subordinate groups of units that are differentiated by the
modifying forces. Each of these subordinate groups, like the original
group, must gradually, in obedience to the influences acting upon it,
lose its balance of parts—must pass from a uniform into a multiform
state. And so on continuously. Whence indeed it is clear that not
only must the homogeneous lapse into the non-homogeneous, but that the
more homogeneous must tend ever to become less homogeneous. If any given
whole, instead of being absolutely uniform throughout, consist of parts
distinguishable from each other—if each of these parts, while somewhat
unlike other parts, is uniform within itself; then, each of them being
in unstable equilibrium, it follows that while the changes set up within
it must render it multiform, they must at the same time render the whole
more multiform than before. The general principle, now to be followed
out in its applications, is thus somewhat more comprehensive than the
title of the chapter implies. No demurrer to the conclusions drawn, can
be based on the ground that perfect homogeneity nowhere exists; since,
whether that state with which we commence be or be not one of perfect
homogeneity, the process must equally be towards a relative
heterogeneity.
* * * * *
§ 110. The stars are distributed with a three-fold irregularity. There
is first the marked contrast between the plane of the milky way and
other parts of the heavens, in respect of the quantities of stars within
given visual areas. There are secondary contrasts of like kind in the
milky way itself, which has its thick and thin places; as well as
throughout the celestial spaces in general, which are much more closely
strewn in some regions than in others. And there is a third order of
contrasts produced by the aggregation of stars into small clusters.
Besides this heterogeneity of distribution of the stars in general,
considered without distinction of kinds, a further such heterogeneity is
disclosed when they are classified by their differences of colour, which
doubtless answer to differences of physical constitution. While the
yellow stars are found in all parts of the heavens, the red and blue
stars are not so: there are wide regions in which both red and blue
stars are rare; there are regions in which the blue occur in
considerable numbers, and there are other regions in which the red are
comparatively abundant. Yet one more irregularity of like significance
is presented by the nebulæ,—aggregations of matter which, whatever be
their nature, most certainly belong to our sidereal system. For the
nebulæ are not dispersed with anything like uniformity; but are abundant
around the poles of the galactic circle and rare in the neighbourhood of
its plane. No one will expect that anything like a definite
interpretation of this structure can be given on the hypothesis of
Evolution, or any other hypothesis. The most that can be looked for is
some reason for thinking that irregularities, not improbably of these
kinds, would occur in the course of Evolution, supposing it to have
taken place. Any one called on to assign such reason might argue, that
if the matter of which stars and all other celestial bodies consist, be
assumed to have originally existed in a diffused form throughout a space
far more vast even than that which our sidereal system now occupies, the
instability of the homogeneous would negative its continuance in that
state. In default of an absolute balance among the forces with which the
dispersed particles acted on each other (which could not exist in any
aggregation having limits) he might show that motion and consequent
changes of distribution would necessarily result. The next step in the
argument would be that in matter of such extreme tenuity and feeble
cohesion there would be motion towards local centres of gravity, as well
as towards the general centre of gravity; just as, to use a humble
illustration, the particles of a precipitate aggregate into flocculi at
the same time that they sink towards the earth. He might urge that in
the one case as in the other, these smallest and earliest local
aggregations must gradually divide into groups, each concentrating to
its own centre of gravity,—a process which must repeat itself on a
larger and larger scale. In conformity with the law that motion once set
up in any direction becomes itself a cause of subsequent motion in that
direction, he might further infer that the heterogeneities thus set up
would tend ever to become more pronounced. Established mechanical
principles would justify him in the conclusion that the motions of these
irregular masses of slightly aggregated nebular matter towards their
common centre of gravity must be severally rendered curvelinear, by the
resistance of the medium from which they were precipitated; and that in
consequence of the irregularities of distribution already set up, such
conflicting curvelinear motions must, by composition of forces, end in a
rotation of the incipient sidereal system. He might without difficulty
show that the resulting centrifugal force must so far modify the process
of general aggregation, as to prevent anything like uniform distribution
of the stars eventually formed—that there must arise a contrast such as
we see between the galactic circle and the rest of the heavens. He might
draw the further not unwarrantable inference, that differences in the
process of local concentration would probably result from the unlikeness
between the physical conditions existing around the general axis of
rotation and those existing elsewhere. To which he might add, that after
the formation of distinct stars, the ever-increasing irregularities of
distribution due to continuance of the same causes would produce that
patchiness which distinguishes the heavens in both its larger and
smaller areas. We need not here however commit ourselves to such
far-reaching speculations. For the purposes of the general argument it
is needful only to show, that any finite mass of diffused matter, even
though vast enough to form our whole sidereal system, could not be in
stable equilibrium; that in default of absolute sphericity, absolute
uniformity of composition, and absolute symmetry of relation to all
forces external to it; its concentration must go on with an
ever-increasing irregularity; and that thus the present aspect of the
heavens is not, so far as we can judge, incongruous with the hypothesis
of a general evolution consequent on the instability of the homogeneous.
Descending to that more limited form of the nebular hypothesis which
regards the solar system as having resulted by gradual concentration;
and assuming this concentration to have advanced so far as to produce a
rotating spheroid of nebulous matter; let us consider what further
consequence the instability of the homogeneous necessitates. Having
become oblate in figure, unlike in the densities of its centre and
surface, unlike in their temperatures, and unlike in the velocities with
which its parts move round their common axis, such a mass can no longer
be called homogeneous; and therefore any further changes exhibited by it
as a whole, can illustrate the general law, only as being changes from a
more homogeneous to a less homogeneous state. Changes of this kind are
to be found in the transformations of such of its parts as are still
homogeneous within themselves. If we accept the conclusion of Laplace,
that the equatorial portion of this rotating and contracting spheroid
will at successive stages acquire a centrifugal force great enough to
prevent any nearer approach to the centre round which it rotates, and
will so be left behind by the inner parts of the spheroid in its
still-continued contraction; we shall find, in the fate of the detached
ring, a fresh exemplification of the principle we are following out.
Consisting of gaseous matter, such a ring, even if absolutely uniform at
the time of its detachment, cannot continue so. To maintain its
equilibrium there must be an almost perfect uniformity in the action of
all external forces upon it (almost, we must say, because the cohesion,
even of extremely attenuated matter, might suffice to neutralize very
minute disturbances); and against this the probabilities are immense. In
the absence of equality among the forces, internal and external, acting
on such a ring, there must be a point or points at which the cohesion of
its parts is less than elsewhere—a point or points at which rupture will
therefore take place. Laplace assumed that the ring would rupture at one
place only; and would then collapse on itself. But this is a more than
questionable assumption—such at least I know to be the opinion of an
authority second to none among those now living. So vast a ring,
consisting of matter having such feeble cohesion, must break up into
many parts. Nevertheless, it is still inferrable from the instability of
the homogeneous, that the ultimate result which Laplace predicted would
take place. For even supposing the masses of nebulous matter into which
such a ring separated, were so equal in their sizes and distances as to
attract each other with exactly equal forces (which is infinitely
improbable); yet the unequal action of external disturbing forces would
inevitably destroy their equilibrium—there would be one or more points
at which adjacent masses would begin to part company. Separation once
commenced, would with ever-accelerating speed lead to a grouping of the
masses. And obviously a like result would eventually take place with the
groups thus formed; until they at length aggregated into a single mass.
Leaving the region of speculative astronomy, let us consider the Solar
System as it at present exists. And here it will be well, in the first
place, to note a fact which may be thought at variance with the
foregoing argument—namely, the still-continued existence of Saturn’s
rings; and especially of the internal nebulous ring lately discovered.
To the objection that the outer rings maintain their equilibrium, the
reply is that the comparatively great cohesion of liquid or solid
substance would suffice to prevent any slight tendency to rupture from
taking effect. And that a nebulous ring here still preserves its
continuity, does not really negative the foregoing conclusion; since it
happens under the quite exceptional influence of those symmetrically
disposed forces which the external rings exercise on it. Here
indeed it deserves to be noted, that though at first sight the Saturnian
system appears at variance with the doctrine that a state of homogeneity
is one of unstable equilibrium, it does in reality furnish a curious
confirmation of this doctrine. For Saturn is not quite concentric with
his rings; and it has been proved mathematically that were he and his
rings concentrically situated, they could not remain so: the homogeneous
relation being unstable, would gravitate into a heterogeneous one. And
this fact serves to remind us of the allied one presented throughout the
whole Solar System. All orbits, whether of planets or satellites, are
more or less excentric—none of them are perfect circles; and were they
perfect circles they would soon become ellipses. Mutual perturbations
would inevitably generate excentricities. That is to say, the
homogeneous relations would lapse into heterogeneous ones.
* * * * *
§ 111. Already so many references have been made to the gradual
formation of a crust over the originally incandescent Earth, that it may
be thought superfluous again to name it. It has not, however, been
before considered in connexion with the general principle under
discussion. Here then it must be noted as a necessary consequence of the
instability of the homogeneous. In this cooling down and solidification
of the Earth’s surface, we have one of the simplest, as well as one of
the most important, instances, of that change from a uniform to a
multiform state which occurs in any mass through exposure of its
different parts to different conditions. To the differentiation of
the Earth’s exterior from its interior thus brought about, we must add
one of the most conspicuous differentiations which the exterior itself
afterwards undergoes, as being similarly brought about. Were the
conditions to which the surface of the Earth is exposed, alike in all
directions, there would be no obvious reason why certain of its parts
should become permanently unlike the rest. But being unequally exposed
to the chief external centre of force—the Sun—its main divisions become
unequally modified: as the crust thickens and cools, there arises that
contrast, now so decided, between the polar and equatorial regions.
Along with these most marked physical differentiations of the Earth,
which are manifestly consequent on the instability of the homogeneous,
there have been going on numerous chemical differentiations, admitting
of similar interpretation. Without raising the question whether, as some
think, the so-called simple substances are themselves compounded of
unknown elements (elements which we cannot separate by artificial heat,
but which existed separately when the heat of the Earth was greater than
any which we can produce),—without raising this question, it will
suffice the present purpose to show how, in place of that comparative
homogeneity of the Earth’s crust, chemically considered, which must have
existed when its temperature was high, there has arisen, during its
cooling, an increasing chemical heterogeneity: each element or compound,
being unable to maintain its homogeneity in presence of various
surrounding affinities, having fallen into heterogeneous combinations.
Let us contemplate this change somewhat in detail. There is every
reason to believe that at an extreme heat, the bodies we call elements
cannot combine. Even under such heat as can be generated artificially,
some very strong affinities yield; and the great majority of chemical
compounds are decomposed at much lower temperatures. Whence it seems not
improbable that, when the Earth was in its first state of incandescence,
there were no chemical combinations at all. But without drawing this
inference, let us set out with the unquestionable fact that the
compounds which can exist at the highest temperatures, and which must
therefore have been the first formed as the Earth cooled, are those of
the simplest constitutions. The protoxides—including under that head the
alkalies, earths, &c.—are, as a class, the most fixed compounds known:
the majority of them resisting decomposition by any heat we can
generate. These, consisting severally of one atom of each component
element, are combinations of the simplest order—are but one degree less
homogeneous than the elements themselves. More heterogeneous than these,
more decomposable by heat, and therefore later in the Earth’s history,
are the deutoxides, tritoxides, peroxides, &c.; in which two, three,
four, or more atoms of oxygen are united with one atom of metal or other
base. Still less able to resist heat, are the salts; which present us
with compound atoms each made up of five, six, seven, eight, ten,
twelve, or more atoms, of three, if not more, kinds. Then there are the
hydrated salts, of a yet greater heterogeneity, which undergo partial
decomposition at much lower temperatures. After them come the
further-complicated supersalts and double salts, having a stability
again decreased; and so throughout. After making a few unimportant
qualifications demanded by peculiar affinities, I believe no chemist
will deny it to be a general law of these inorganic combinations that,
other things equal, the stability decreases as the complexity increases.
And then when we pass to the compounds that make up organic bodies, we
find this general law still further exemplified: we find much greater
complexity and much less stability. An atom of albumen, for instance,
consists of 482 ultimate atoms of five different kinds. Fibrine, still
more intricate in constitution, contains in each atom, 298 atoms of
carbon, 49 of nitrogen, 2 of sulphur, 228 of hydrogen, and 92 of
oxygen—in all, 660 atoms; or, more strictly speaking—equivalents. And
these two substances are so unstable as to decompose at quite moderate
temperatures; as that to which the outside of a joint of roast meat is
exposed. Possibly it will be objected that some inorganic compounds, as
phosphuretted hydrogen and chloride of nitrogen, are more decomposable
than most organic compounds. This is true. But the admission may be made
without damage to the argument. The proposition is not that _all_ simple
combinations are more fixed than _all_ complex ones. To establish our
inference it is necessary only to show that, as an _average fact_, the
simple combinations can exist at a higher temperature than the complex
ones. And this is wholly beyond question. Thus it is manifest that
the present chemical heterogeneity of the Earth’s surface has arisen by
degrees as the decrease of heat has permitted; and that it has shown
itself in three forms—first, in the multiplication of chemical
compounds; second, in the greater number of different elements contained
in the more modern of these compounds; and third, in the higher and more
varied multiples in which these more numerous elements combine.
Without specifying them, it will suffice just to name the meteorologic
processes eventually set up in the Earth’s atmosphere, as further
illustrating the alleged law. They equally display that destruction of a
homogeneous state which results from unequal exposure to incident
forces.
* * * * *
§ 112. Take a mass of unorganized but organizable matter—either the body
of one of the lowest living forms, or the germ of one of the higher.
Consider its circumstances. Either it is immersed in water or air, or it
is contained within a parent organism. Wherever placed, however, its
outer and inner parts stand differently related to surrounding
agencies—nutriment, oxygen, and the various stimuli. But this is not
all. Whether it lies quiescent at the bottom of the water or on the leaf
of a plant; whether it moves through the water preserving some definite
attitude; or whether it is in the inside of an adult; it equally results
that certain parts of its surface are more exposed to surrounding
agencies than other parts—in some cases more exposed to light, heat, or
oxygen, and in others to the maternal tissues and their contents. Hence
must follow the destruction of its original equilibrium. This may take
place in one of two ways. Either the disturbing forces may be such as to
overbalance the affinities of the organic elements, in which case there
result those changes which are known as decomposition; or, as is
ordinarily the case, such changes are induced as do not destroy the
organic compounds, but only modify them: the parts most exposed to the
modifying forces being most modified. To elucidate this, suppose we take
a few cases.
Note first what appear to be exceptions. Certain minute animal forms
present us either with no appreciable differentiations or with
differentiations so obscure as to be made out with great difficulty. In
the Rhizopods, the substance of the jelly-like body remains throughout
life unorganized, even to the extent of having no limiting membrane; as
is proved by the fact that the thread-like processes protruded by the
mass, coalesce on touching each other. Whether or not the nearly allied
_Amœba_, of which the less numerous and more bulky processes do not
coalesce, has, as lately alleged, something like a cell-wall and a
nucleus, it is clear that the distinction of parts is very slight; since
particles of food pass bodily into the inside through any part of the
periphery, and since when the creature is crushed to pieces, each piece
behaves as the whole did. Now these cases, in which there is either no
contrast of structure between exterior and interior or very little,
though seemingly opposed to the above inference, are really very
significant evidences of its truth. For what is the peculiarity of this
division of the _Protozoa_? Its members undergo perpetual and irregular
changes of form—they show no persistent relation of parts. What lately
formed a portion of the interior is now protruded, and, as a temporary
limb, is attached to some object it happens to touch. What is now a part
of the surface will presently be drawn, along with the atom of nutriment
sticking to it, into the centre of the mass. Either the relations of
inner and outer have no permanent existence, or they are very slightly
marked. But by the hypothesis, it is only because of their unlike
positions with respect to modifying forces, that the originally like
units of a living mass become unlike. We must therefore expect no
established differentiation of parts in creatures which exhibit no
established differences of position in their parts; and we must expect
extremely little differentiation of parts where the differences of
position are but little determined—which is just what we find.
This negative evidence is borne out by positive evidence. When we
turn from these proteiform specks of living jelly to organisms having an
unchanging distribution of substance, we find differences of tissue
corresponding to differences of relative position. In all the higher
_Protozoa_, as also in the _Protophyta_, we meet with a fundamental
differentiation into cell-membrane and cell-contents; answering to that
fundamental contrast of conditions implied by the terms outside and
inside. On passing from what are roughly classed as unicellular
organisms, to the lowest of those which consist of aggregated cells, we
equally observe the connection between structural differences and
differences of circumstance. Negatively, we see that in the sponge,
permeated throughout by currents of sea-water, the indefiniteness of
organization corresponds with the absence of definite unlikeness of
conditions: the peripheral and central portions are as little contrasted
in structure as in exposure to surrounding agencies. While positively,
we see that in a form like the _Thalassicolla_, which, though equally
humble, maintains its outer and inner parts in permanently unlike
circumstances, there is displayed a rude structure obviously
subordinated to the primary relations of centre and surface: in all its
many and important varieties, the parts exhibit a more or less
concentric arrangement.
After this primary modification, by which the outer tissues are
differentiated from the inner, the next in order of constancy and
importance is that by which some part of the outer tissues is
differentiated from the rest; and this corresponds with the almost
universal fact that some part of the outer tissues is more exposed to
certain environing influences than the rest. Here, as before, the
apparent exceptions are extremely significant. Some of the lowest
vegetal organisms, as the _Hematococci_ and _Protococci_, evenly
imbedded in a mass of mucus, or dispersed through the Arctic snow,
display no differentiations of surface; the several parts of their
surfaces being subjected to no definite contrasts of conditions.
Ciliated spheres such as the _Volvox_ have no parts of their periphery
unlike other parts; and it is not to be expected that they should have;
since, as they revolve in all directions, they do not, in traversing the
water, permanently expose any part to special conditions. But when we
come to organisms that are either fixed, or while moving preserve
definite attitudes, we no longer find uniformity of surface. The most
general fact which can be asserted with respect to the structures of
plants and animals, is, that however much alike in shape and texture the
various parts of the exterior may at first be, they acquire unlikenesses
corresponding to the unlikenesses of their relations to surrounding
agencies. The ciliated germ of a Zoophyte, which, during its locomotive
stage, is distinguishable only into outer and inner tissues, no sooner
becomes fixed, than its upper end begins to assume a different structure
from its lower. The disc-shaped _gemmæ_ of the _Marchantia_, originally
alike on both surfaces, and falling at random with either side
uppermost, immediately begin to develop rootlets on the under side, and
_stomata_ on the upper side: a fact proving beyond question, that this
primary differentiation is determined by this fundamental contrast of
conditions.
Of course in the germs of higher organisms, the metamorphoses
immediately due to the instability of the homogeneous, are soon masked
by those due to the assumption of the hereditary type. Such early
changes, however, as are common to all classes of organisms, and so
cannot be ascribed to heredity, entirely conform to the hypothesis. A
germ which has undergone no developmental modifications, consists of a
spheroidal group of homogeneous cells. Universally, the first step in
its evolution is the establishment of a difference between some of the
peripheral cells and the cells which form the interior—some of the
peripheral cells, after repeated spontaneous fissions, coalesce into a
membrane; and by continuance of the process this membrane spreads until
it speedily invests the entire mass, as in mammals, or, as in birds,
stops short of that for some time. Here we have two significant facts.
The first is, that the primary unlikeness arises between the exterior
and the interior. The second is, that the change which thus initiates
development, does not take place simultaneously over the whole exterior;
but commences at one place, and gradually involves the rest. Now these
facts are just those which might be inferred from the instability of the
homogeneous. The surface must, more than any other part, become unlike
the centre, because it is most dissimilarly conditioned; and all parts
of the surface cannot simultaneously exhibit this differentiation,
because they cannot be exposed to the incident forces with absolute
uniformity. One other general fact of like implication remains.
Whatever be the extent of this peripheral layer of cells, or blastoderm
as it is called, it presently divides into two layers—the serous and
mucous; or, as they have been otherwise called, the ectoderm and the
endoderm. The first of these is formed from that portion of the layer
which lies in contact with surrounding agents; and the second of them is
formed from that portion of the layer which lies in contact with the
contained mass of yelk. That is to say, after the primary
differentiation, more or less extensive, of surface from centre, the
resulting superficial portion undergoes a secondary differentiation into
inner and outer parts—a differentiation which is clearly of the same
order with the preceding, and answers to the next most marked contrast
of conditions.
But, as already hinted, this principle, understood in the simple form
here presented, supplies no key to the detailed phenomena of organic
development. It fails entirely to explain generic and specific
peculiarities; and indeed leaves us equally in the dark respecting those
more important distinctions by which families and orders are marked out.
Why two ova, similarly exposed in the same pool, should become the one a
fish, and the other a reptile, it cannot tell us. That from two
different eggs placed under the same hen, should respectively come forth
a duckling and a chicken, is a fact not to be accounted for on the
hypothesis above developed. We have here no alternative but to fall back
upon the unexplained principle of hereditary transmission. The capacity
possessed by an unorganized germ of unfolding into a complex adult,
which repeats ancestral traits in the minutest details, and that even
when it has been placed in conditions unlike those of its ancestors, is
a capacity we cannot at present understand. That a microscopic portion
of seemingly structureless matter should embody an influence of such
kind, that the resulting man will in fifty years after become gouty or
insane, is a truth which would be incredible were it not daily
illustrated. Should it however turn out, as we shall hereafter
find reason for suspecting, that these complex differentiations which
adults exhibit, are themselves the slowly accumulated and transmitted
results of a process like that seen in the first changes of the germ; it
will follow that even those embryonic changes due to hereditary
influence, are remote consequences of the alleged law. Should it be
shown that the slight modifications wrought during life on each adult,
and bequeathed to offspring along with all like preceding modifications,
are themselves unlikenesses of parts that are produced by unlikenesses
of conditions; then it will follow that the modifications displayed in
the course of embryonic development, are partly direct consequences of
the instability of the homogeneous, and partly indirect consequences of
it. To give reasons for entertaining this hypothesis, however, is
not needful for the justification of the position here taken. It is
enough that the most conspicuous differentiations which incipient
organisms universally display, correspond to the most marked differences
of conditions to which their parts are subject. It is enough that the
habitual contrast between outside and inside, which we _know_ is
produced in inorganic masses by unlikeness of exposure to incident
forces, is strictly paralleled by the first contrast that makes its
appearance in all organic masses.
It remains to point out that in the assemblage of organisms
constituting a species, the principle enunciated is equally traceable.
We have abundant materials for the induction that each species will
not remain uniform, but is ever becoming to some extent multiform; and
there is ground for the deduction that this lapse from homogeneity to
heterogeneity is caused by the subjection of its members to unlike
sets of circumstances. The fact that in every species, animal and
vegetal, the individuals are never quite alike; joined with the fact
that there is in every species a tendency to the production of
differences marked enough to constitute varieties; form a sufficiently
wide basis for the induction. While the deduction is confirmed by the
familiar experience that varieties are most numerous and decided
where, as among cultivated plants and domestic animals, the conditions
of life depart from the original ones, most widely and in the most
numerous ways. Whether we regard “natural selection” as wholly, or
only in part, the agency through which varieties are established,
matters not to the general conclusion. For as the survival of any
variety proves its constitution to be in harmony with a certain
aggregate of surrounding forces—as the multiplication of a variety and
the usurpation by it of an area previously occupied by some other part
of the species, implies different effects produced by such aggregate
of forces on the two, it is clear that this aggregate of forces is the
real cause of the differentiation—it is clear that if the variety
supplants the original species in some localities but not in others,
it does so because the aggregate of forces in the one locality is
unlike that in the other—it is clear that the lapse of the species
from a state of homogeneity to a state of heterogeneity arises from
the exposure of its different parts to different aggregates of forces.
* * * * *
§ 113. Among mental phenomena it is difficult to establish the alleged
law without an analysis too extensive for the occasion. To show
satisfactorily how states of consciousness, originally homogeneous,
become heterogeneous through differences in the changes wrought by
different forces, would require us carefully to trace out the
organization of early experiences. Were this done it would become
manifest that the development of intelligence, is, under one of its
chief aspects, a dividing into separate classes, the unlike things
previously confounded together in one class—a formation of sub-classes
and sub-sub-classes, until the once confused aggregate of objects known,
is resolved into an aggregate which unites extreme heterogeneity among
its multiplied groups, with complete homogeneity among the members of
each group. If, for example, we followed, through ascending grades of
creatures, the genesis of that vast structure of knowledge acquired by
sight, we should find that in the first stage, where eyes suffice for
nothing beyond the discrimination of light from darkness, the only
possible classifications of objects seen, must be those based on the
manner in which light is obstructed, and the degree in which it is
obstructed. We should find that by such undeveloped visual organs, the
shadows traversing the rudimentary retina would be merely distinguished
into those of the stationary objects which the creature passed during
its own movements, and those of the moving objects which came near the
creature while it was at rest; and that so the extremely general
classification of visible things into stationary and moving, would be
the earliest formed. We should find that whereas the simplest eyes are
not fitted to distinguish between an obstruction of light caused by a
small object close to, and an obstruction caused by a large object at
some distance, eyes a little more developed must be competent to such a
distinction; whence must result a vague differentiation of the class of
moving objects, into the nearer and the more remote. We should find that
such further improvements in vision as those which make possible a
better estimation of distances by adjustment of the optic axes, and
those which, through enlargement and subdivision of the retina, make
possible the discrimination of shapes, must have the effects of giving
greater definiteness to the classes already formed, and of sub-dividing
these into smaller classes, consisting of objects less unlike. And we
should find that each additional refinement of the perceptive organs,
must similarly lead to a multiplication of divisions and a sharpening of
the limits of each division. In every infant might be traced the
analogous transformation of a confused aggregate of impressions of
surrounding objects, not recognized as differing in their distances,
sizes, and shapes, into separate classes of objects unlike each other in
these and various other respects. And in the one case as in the other,
it might be shown that the change from this first indefinite, incoherent
and comparatively homogeneous consciousness, to a definite, coherent,
and heterogeneous one, is due to differences in the actions of incident
forces on the organism. These brief indications of what might be
shown, did space permit, must here suffice. Probably they will give
adequate clue to an argument by which each reader may satisfy himself
that the course of mental evolution offers no exception to the general
law. In further aid of such an argument, I will here add an illustration
that is comprehensible apart from the process of mental evolution as a
whole.
It has been remarked (I am told by Coleridge, though I have been unable
to find the passage) that with the advance of language, words which were
originally alike in their meanings acquire unlike meanings—a change
which he expresses by the formidable word “desynonymization.” Among
indigenous words this loss of equivalence cannot be clearly shown;
because in them the divergencies of meaning began before the dawn of
literature. But among words that have been coined, or adopted from other
languages, since the writing of books commenced, it is demonstrable. In
the old divines, _miscreant_ is used in its etymological sense of
_unbeliever_; but in modern speech it has entirely lost this sense.
Similarly with _evil-doer_ and _malefactor_: exactly synonymous as these
are by derivation, they are no longer synonymous by usage: by a
_malefactor_ we now understand a convicted criminal, which is far from
being the acceptation of _evil-doer_. The verb _produce_, bears in
Euclid its primary meaning—to _prolong_, or _draw out_; but the now
largely developed meanings of _produce_ have little in common with the
meanings of _prolong_, or _draw out_. In the Church of England liturgy,
an odd effect results from the occurrence of _prevent_ in its original
sense—_to come before_, instead of its modern specialized sense—_to come
before with the effect of arresting_. But the most conclusive cases are
those in which the contrasted words consist of the same parts
differently combined; as in _go under_ and _undergo_. We _go under_ a
tree, and we _undergo_ a pain. But though, if analytically considered,
the meanings of these expressions would be the same were the words
transposed, habit has so far modified their meanings that we could not
without absurdity speak of _undergoing_ a tree and _going under_ a pain.
Countless such instances might be brought to show that between two
words which are originally of like force, an equilibrium cannot be
maintained. Unless they are daily used in exactly equal degrees, in
exactly similar relations (against which there are infinite
probabilities), there necessarily arises a habit of associating one
rather than the other with particular acts, or objects. Such a habit,
once commenced, becomes confirmed; and gradually their homogeneity of
meaning disappears. In each individual we may see the tendency which
inevitably leads to this result. A certain vocabulary and a certain set
of phrases, distinguish the speech of each person: each person
habitually uses certain words in places where other words are habitually
used by other persons; and there is a continual recurrence of favourite
expressions. This inability to maintain a balance in the use of verbal
symbols, which characterizes every man, characterizes, by consequence,
aggregates of men; and the desynonymization of words is the ultimate
effect.
Should any difficulty be felt in understanding how these mental changes
exemplify a law of physical transformations that are wrought by physical
forces, it will disappear on contemplating acts of mind as nervous
functions. It will be seen that each loss of equilibrium above
instanced, is a loss of functional equality between some two elements of
the nervous system. And it will be seen that, as in other cases, this
loss of functional equality is due to differences in the incidence of
forces.
* * * * *
§ 114. Masses of men, in common with all other masses, show a like
proclivity similarly caused. Small combinations and large societies
equally manifest it; and in the one, as in the other, both governmental
and industrial differentiations are initiated by it. Let us glance at
the facts under these two heads.
A business partnership, balanced as the authorities of its members may
theoretically be, practically becomes a union in which the authority of
one partner is tacitly recognized as greater than that of the other or
others. Though the shareholders have given equal powers to the directors
of their company, inequalities of power soon arise among them; and
usually the supremacy of some one director grows so marked, that his
decisions determine the course which the board takes. Nor in
associations for political, charitable, literary, or other purposes, do
we fail to find a like process of division into dominant and subordinate
parties; each having its leader, its members of less influence, and its
mass of uninfluential members. These minor instances in which
unorganized groups of men, standing in homogeneous relations, may be
watched gradually passing into organized groups of men standing in
heterogeneous relations, give us the key to social inequalities.
Barbarous and civilized communities are alike characterized by
separation into classes, as well as by separation of each class into
more important and less important units; and this structure is
manifestly the gradually-consolidated result of a process like that
daily exemplified in trading and other combinations. So long as men are
constituted to act on one another, either by physical force or by force
of character, the struggles for supremacy must finally be decided in
favour of some one; and the difference once commenced must tend to
become ever more marked. Its unstable equilibrium being destroyed, the
uniform must gravitate with increasing rapidity into the multiform. And
so supremacy and subordination must establish themselves, as we see they
do, throughout the whole structure of a society, from the great
class-divisions pervading its entire body, down to village cliques, and
even down to every posse of school-boys. Probably it will be
objected that such changes result, not from the homogeneity of the
original aggregations, but from their non-homogeneity—from certain
slight differences existing among their units at the outset. This is
doubtless the proximate cause. In strictness, such changes must be
regarded as transformations of the relatively homogeneous into the
relatively heterogeneous. But it is abundantly clear that an aggregation
of men, absolutely alike in their endowments, would eventually undergo a
similar transformation. For in the absence of perfect uniformity in the
lives severally led by them—in their occupations, physical conditions,
domestic relations, and trains of thought and feeling—there must arise
differences among them; and these must finally initiate social
differentiations. Even inequalities of health caused by accidents, must,
by entailing inequalities of physical and mental power, disturb the
exact balance of mutual influences among the units; and the balance once
disturbed, must inevitably be lost. Whence, indeed, besides seeing that
a body of men absolutely homogeneous in their governmental relations,
must, like all other homogeneous bodies, become heterogeneous, we also
see that it must do this from the same ultimate cause—unequal exposure
of its parts to incident forces.
The first industrial divisions of societies are much more obviously due
to unlikenesses of external circumstances. Such divisions are absent
until such unlikenesses are established. Nomadic tribes do not
permanently expose any groups of their members to special local
conditions; nor does a stationary tribe, when occupying only a small
area, maintain from generation to generation marked contrasts in the
local conditions of its members; and in such tribes there are no decided
economical differentiations. But a community which, growing populous,
has overspread a large tract, and has become so far settled that its
members live and die in their respective districts, keeps its several
sections in different physical circumstances; and then they no longer
remain alike in their occupations. Those who live dispersed continue to
hunt or cultivate the earth; those who spread to the sea-shore fall into
maritime occupations; while the inhabitants of some spot chosen, perhaps
for its centrality, as one of periodical assemblage, become traders, and
a town springs up. Each of these classes undergoes a modification of
character consequent on its function, and better fitting it to its
function. Later in the process of social evolution these local
adaptations are greatly multiplied. A result of differences in soil and
climate, is that the rural inhabitants in different parts of the kingdom
have their occupations partially specialized; and become respectively
distinguished as chiefly producing cattle, or sheep, or wheat, or oats,
or hops, or cyder. People living where coal-fields are discovered are
transformed into colliers; Cornishmen take to mining because Cornwall is
metalliferous; and the iron-manufacture is the dominant industry where
ironstone is plentiful. Liverpool has assumed the office of importing
cotton, in consequence of its proximity to the district where cotton
goods are made; and for analogous reasons, Hull has become the chief
port at which foreign wools are brought in. Even in the establishment of
breweries, of dye-works, of slate-quarries, of brickyards, we may see
the same truth. So that both in general and in detail, the
specializations of the social organism which characterize separate
districts, primarily depend on local circumstances. Those divisions of
labour which under another aspect were interpreted as due to the setting
up of motion in the directions of least resistance (§ 91), are here
interpreted as due to differences in the incident forces; and the two
interpretations are quite consistent with each other. For that which in
each case _determines_ the direction of least resistance, is the
distribution of the forces to be overcome; and hence unlikenesses of
distribution in separate localities, entails unlikenesses in the course
of human action in those localities—entails industrial differentiations.
* * * * *
§ 115. In common with the general truths set forth in preceding
chapters, the instability of the homogeneous is demonstrable _à priori_.
It, like each of them, is a corollary from the persistence of force.
Already this has been tacitly implied by assigning unlikeness in the
exposure of its part to surrounding agencies, as the reason why a
uniform mass loses its uniformity. But here it will be proper to expand
this tacit implication into definite proof.
On striking a mass of matter with such force as either to indent it or
make it fly to pieces, we see both that the blow affects differently its
different parts, and that the differences are consequent on the unlike
relations of its parts to the force impressed. The part with which the
striking body comes in contact, receiving the whole of the communicated
momentum, is driven in towards the centre of the mass. It thus
compresses and tends to displace the more centrally situated portions of
the mass. These, however, cannot be compressed or thrust out of their
places without pressing on all surrounding portions. And when the blow
is violent enough to fracture the mass, we see, in the radial dispersion
of its fragments, that the original momentum, in being distributed
throughout it, has been divided into numerous minor momenta, unlike in
their directions. We see that these directions are determined by the
positions of the parts with respect to each other, and with respect to
the point of impact. We see that the parts are differently affected by
the disruptive force, because they are differently related to it in
their directions and attachments—that the effects being the joint
products of the cause and the conditions, cannot be alike in parts which
are differently conditioned. A body on which radiant heat is
falling, exemplifies this truth still more clearly. Taking the simplest
case (that of a sphere) we see that while the part nearest to the
radiating centre receives the rays at right angles, the rays strike the
other parts of the exposed side at all angles from 90° down to 0°.
Again, the molecular vibrations propagated through the mass from the
surface which receives the heat, must proceed inwards at angles
differing for each point. Further, the interior parts of the sphere
affected by the vibrations proceeding from all points of the heated
side, must be dissimilarly affected in proportion as their positions are
dissimilar. So that whether they be on the recipient area, in the
middle, or at the remote side, the constituent atoms are all thrown into
states of vibration more or less unlike each other.
But now, what is the ultimate meaning of the conclusion that a uniform
force produces different changes throughout a uniform mass, because the
parts of the mass stand in different relations to the force? Fully to
understand this, we must contemplate each part as simultaneously subject
to other forces—those of gravitation, of cohesion, of molecular motion,
&c. The effect wrought by an additional force, must be a resultant of it
and the forces already in action. If the forces already in action on two
parts of any aggregate, are different in their directions, the effects
produced on these two parts by like forces must be different in their
directions. Why must they be different? They must be different because
such unlikeness as exists between the two sets of factors, is made by
the presence in the one of some specially-directed force that is not
present in the other; and that this force will produce an effect,
rendering the total result in the one case unlike that in the other, is
a necessary corollary from the persistence of force. Still more
manifest does it become that the dissimilarly-placed parts of any
aggregate must be dissimilarly modified by an incident force, when we
remember that the _quantities_ of the incident force to which they are
severally subject, are not equal, as above supposed; but are nearly
always very unequal. The outer parts of masses are usually alone exposed
to chemical actions; and not only are their inner parts shielded from
the affinities of external elements, but such affinities are brought to
bear unequally on their surfaces; since chemical action sets up currents
through the medium in which it takes place, and so brings to the various
parts of the surface unequal quantities of the active agent. Again, the
amounts of any external radiant force which the different parts of an
aggregate receive, are widely contrasted: we have the contrast between
the quantity falling on the side next the radiating centre, and the
quantity, or rather no quantity, falling on the opposite side; we have
contrasts in the quantities received by differently-placed areas on the
exposed side; and we have endless contrasts between the quantities
received by the various parts of the interior. Similarly when mechanical
force is expended on any aggregate, either by collision, continued
pressure, or tension, the amounts of strain distributed throughout the
mass are manifestly unlike for unlike positions. But to say the
different parts of an aggregate receive different quantities of any
incident force, is to say that their states are modified by it in
different degrees—is to say that if they were before homogeneous in
their relations they must be rendered to a proportionate extent
heterogeneous; since, force being persistent, the different quantities
of it falling on the different parts, must work in them different
quantities of effect—different changes. Yet one more kindred
deduction is required to complete the argument. We may, by parallel
reasoning, reach the conclusion that, even apart from the action of any
external force, the equilibrium of a homogeneous aggregate must be
destroyed by the unequal actions of its parts on each other. That mutual
influence which produces aggregation (not to mention other mutual
influences) must work different effects on the different parts; since
they are severally exposed to it in unlike amounts and directions. This
will be clearly seen on remembering that the portions of which the whole
is made up, may be severally regarded as minor wholes; that on each of
these minor wholes, the action of the entire aggregate then becomes an
external incident force; that such external incident force must, as
above shown, work unlike changes in the parts of any such minor whole;
and that if the minor wholes are severally thus rendered heterogeneous,
the entire aggregate is rendered heterogeneous.
The instability of the homogeneous is thus deducible from that
primordial truth which underlies our intelligence. One stable
homogeneity only, is hypothetically possible. If centres of force,
absolutely uniform in their powers, were diffused with absolute
uniformity through unlimited space, they would remain in equilibrium.
This however, though a verbally intelligible supposition, is one that
cannot be represented in thought; since unlimited space is
inconceivable. But all finite forms of the homogeneous—all forms of it
which we can know or conceive, must inevitably lapse into heterogeneity.
In three several ways does the persistence of force necessitate this.
Setting external agencies aside, each unit of a homogeneous whole must
be differently affected from any of the rest by the aggregate action of
the rest upon it. The resultant force exercised by the aggregate on each
unit, being in no two cases alike in both amount and direction, and
usually not in either, any incident force, even if uniform in amount and
direction, cannot produce like effects on the units. And the various
positions of the parts in relation to any incident force, preventing
them from receiving it in uniform amounts and directions, a further
difference in the effects wrought on them is inevitably produced.
One further remark is needed. To the conclusion that the changes with
which Evolution _commences_, are thus necessitated, remains to be added
the conclusion that these changes must _continue_. The absolutely
homogeneous must lose its equilibrium; and the relatively homogeneous
must lapse into the relatively less homogeneous. That which is true of
any total mass, is true of the parts into which it segregates. The
uniformity of each such part must as inevitably be lost in multiformity,
as was that of the original whole; and for like reasons. And thus the
continued changes which characterize Evolution, in so far as they are
constituted by the lapse of the homogeneous into the heterogeneous, and
of the less heterogeneous into the more heterogeneous, are necessary
consequences of the persistence of force.
-----
Footnote 16:
The idea developed in this chapter originally formed part of an
article on “Transcendental Physiology,” published in 1857. See
_Essays_, pp. 279–290.