DIFFERENTIATION AND INTEGRATION.
§ 123. The general interpretation of Evolution is far from being
completed in the preceding chapters. We must contemplate its changes
under yet another aspect, before we can form a definite conception of
the process constituted by them. Though the laws already set forth,
furnish a key to the re-arrangement of parts which Evolution exhibits,
in so far as it is an advance from the uniform to the multiform; they
furnish no key to this re-arrangement in so far as it is an advance from
the indefinite to the definite. On studying the actions and re-actions
everywhere going on, we have found it to follow inevitably from a
certain primordial truth, that the homogeneous must lapse into the
heterogeneous, and that the heterogeneous must become more
heterogeneous; but we have not discovered why the differently-affected
parts of any simple whole, become clearly marked off from each other, at
the same time that they become unlike. Thus far no reason has been
assigned why there should not ordinarily arise a vague chaotic
heterogeneity, in place of that orderly heterogeneity displayed in
Evolution. It still remains to find out the cause of that integration of
parts which accompanies their differentiation—that gradually-completed
segregation of like units into a group, distinctly separated from
neighbouring groups which are severally made up of other kinds of units.
The rationale will be conveniently introduced by a few instances in
which we may watch this segregative process taking place.
When towards the end of September, the trees are gaining their autumn
colours, and we are hoping shortly to see a further change increasing
still more the beauty of the landscape, we are not uncommonly
disappointed by the occurrence of an equinoxial gale. Out of the mixed
mass of foliage on each branch, the strong current of air carries away
the decaying and brightly-tinted leaves, but fails to detach those which
are still green. And while these last, frayed and seared by
long-continued beatings against each other, and the twigs around them,
give a sombre colour to the woods, the red and yellow and orange leaves
are collected together in ditches and behind walls and in corners where
eddies allow them to settle. That is to say, by the action of that
uniform force which the wind exerts on both kinds, the dying leaves are
picked out from among their still living companions and gathered in
places by themselves. Again, the separation of particles of different
sizes, as dust and sand from pebbles, may be similarly effected; as we
see on every road in March. And from the days of Homer downwards, the
power of currents of air, natural and artificial, to part from one
another units of unlike specific gravities, has been habitually utilized
in the winnowing of chaff from wheat. In every river we see how
the mixed materials carried down, are separately deposited—how in rapids
the bottom gives rest to nothing but boulders and pebbles; how where the
current is not so strong, sand is let fall; and how, in still places,
there is a sediment of mud. This selective action of moving water, is
commonly applied in the arts to obtain masses of particles of different
degrees of fineness. Emery, for example, after being ground, is carried
by a slow current through successive compartments; in the first of which
the largest grains subside; in the second of which the grains that reach
the bottom before the water has escaped, are somewhat smaller; in the
third smaller still; until in the last there are deposited only those
finest particles which fall so slowly through the water, that they have
not previously been able to reach the bottom. And in a way that is
different though equally significant, this segregative effect of water
in motion, is exemplified in the carrying away of soluble from insoluble
matters—an application of it hourly made in every laboratory. The
effects of the uniform forces which aerial and aqueous currents
exercise, are paralleled by those of uniform forces of other orders.
Electric attraction will separate small bodies from large, or light
bodies from heavy. By magnetism, grains of iron may be selected from
among other grains; as by the Sheffield grinder, whose magnetized gauze
mask filters out the steel-dust which his wheel gives off, from the
stone-dust that accompanies it. And how the affinity of any agent acting
differently on the components of a given body, enables us to take away
some component and leave the rest behind, is shown in almost every
chemical experiment.
What now is the general truth here variously presented? How are these
several facts and countless similar ones, to be expressed in terms that
embrace them all? In each case we see in action a force which may be
regarded as simple or uniform—fluid motion in a certain direction at a
certain velocity; electric or magnetic attraction of a given amount;
chemical affinity of a particular kind: or rather, in strictness, the
acting force is compounded of one of these and certain other uniform
forces, as gravitation, etc. In each case we have an aggregate made up
of unlike units—either atoms of different substances combined or
intimately mingled, or fragments of the same substance of different
sizes, or other constituent parts that are unlike in their specific
gravities, shapes, or other attributes. And in each case these unlike
units, or groups of units, of which the aggregate consists, are, under
the influence of some resultant force acting indiscriminately on them
all, separated from each other—segregated into minor aggregates, each
consisting of units that are severally like each other and unlike those
of the other minor aggregates. Such being the common aspect of these
changes, let us look for the common interpretation of them.
In the chapter on “The Instability of the Homogeneous,” it was shown
that a uniform force falling on any aggregate, produces unlike
modifications in its different parts—turns the uniform into the
multiform and the multiform into the more multiform. The transformation
thus wrought, consists of either insensible or sensible changes of
relative position among the units, or of both—either of those molecular
re-arrangements which we call chemical, or of those larger
transpositions which are distinguished as mechanical, or of the two
united. Such portion of the permanently effective force as reaches each
different part, or differently-conditioned part, may be expended in
modifying the mutual relations of its constituents; or it may be
expended in moving the part to another place; or it may be expended
partially in the first and partially in the second. Hence, so much of
the permanently effective force as does not work the one kind of effect,
must work the other kind. It is manifest that if of the permanently
effective force which falls on some compound unit of an aggregate,
little, if any, is absorbed in re-arranging the ultimate components of
such compound unit, much or the whole, must show itself in motion of
such compound unit to some other place in the aggregate; and conversely,
if little or none of this force is absorbed in generating mechanical
transposition, much or the whole must go to produce molecular
alterations. What now must follow from this? In cases where none
or only part of the force generates chemical re-distributions, what
physical re-distributions must be generated? Parts that are similar to
each other will be similarly acted on by the force; and will similarly
react on it. Parts that are dissimilar will be dissimilarly acted on by
the force; and will dissimilarly react on it. Hence the permanently
effective incident force, when wholly or partially transformed into
mechanical motion of the units, will produce like motions in units that
are alike, and unlike motions in units that are unlike. If then, in an
aggregate containing two or more orders of mixed units, those of the
same order will be moved in the same way, and in a way that differs from
that in which units of other orders are moved, the respective orders
must segregate. A group of like things on which are impressed motions
that are alike in amount and direction, must be transferred as a group
to another place, and if they are mingled with some group of other
things, on which the motions impressed are like each other, but unlike
those of the first group in amount or direction or both, these other
things must be transferred as a group to some other place—the mixed
aggregate must undergo a simultaneous differentiation and integration.
In further elucidation of this process, it will be well here to set down
a few instances in which we may see that, other things equal, the
definiteness of the separation is in proportion to the definiteness of
the difference between the units. Take a handful of any pounded
substance, containing fragments of all sizes; and let it fall to the
ground while a gentle breeze is blowing. The large fragments will be
collected together on the ground almost immediately under the hand;
somewhat smaller fragments will be carried a little to the leeward;
still smaller ones a little further; and those minute particles which we
call dust, will be drifted a long way before they reach the earth: that
is, the integration is indefinite where the difference among the
fragments is indefinite, though the divergence is greatest where the
difference is greatest. If, again, the handful be made up of quite
distinct orders of units—as pebbles, coarse sand, and dust—these will,
under like conditions, be segregated with comparative definiteness: the
pebbles will drop almost vertically; the sand will fall in an inclined
direction, and deposit itself within a tolerably circumscribed space
beyond the pebbles; while the dust will be blown almost horizontally to
a great distance. A case in which another kind of force comes into play,
will still better illustrate this truth. Through a mixed aggregate of
soluble and insoluble substances, let water slowly percolate. There will
in the first place be a distinct parting of the substances that are the
most widely contrasted in their relations to the acting forces: the
soluble will be carried away; the insoluble will remain behind. Further,
some separation, though a less definite one, will be effected among the
soluble substances; since the first part of the current will remove the
most soluble substances in the largest amounts, and after these have
been all dissolved, the current will still continue to bring out the
remaining less soluble substances. Even the undissolved matters will
have simultaneously undergone a certain segregation; for the percolating
fluid will carry down the minute fragments from among the large ones,
and will deposit those of small specific gravity in one place, and those
of great specific gravity in another. To complete the elucidation
we must glance at the obverse fact; namely, that mixed units which
differ but slightly, are moved in but slightly-different ways by
incident forces, and can therefore be separated only by such adjustments
of the incident forces as allow slight differences to become appreciable
factors in the result. This truth is made manifest by antithesis in the
instances just given; but it may be made much more manifest by a few
such instances as those which chemical analysis supplies in abundance.
The parting of alcohol from water by distillation is a good one. Here we
have atoms consisting of oxygen and hydrogen, mingled with atoms
consisting of oxygen, hydrogen, and carbon. The two orders of atoms have
a considerable similarity of nature: they similarly maintain a fluid
form at ordinary temperatures; they similarly become gaseous more and
more rapidly as the temperature is raised; and they boil at points not
very far apart. Now this comparative likeness of the atoms is
accompanied by difficulty in segregating them. If the mixed fluid is
unduly heated, much water distils over with the alcohol: it is only
within a narrow range of temperature, that the one set of atoms are
driven off rather than the others; and even then not a few of the others
accompany them. The most interesting and instructive example, however,
is furnished by certain phenomena of crystallization. When several salts
that have little analogy of constitution, are dissolved in the same body
of water, they are separated without much trouble, by crystallization:
their respective units moved towards each other, as physicists suppose,
by polar forces, segregate into crystals of their respective kinds. The
crystals of each salt do, indeed, usually contain certain small amounts
of the other salts present in the solution—especially when the
crystallization has been rapid; but from these other salts they are
severally freed by repeated resolutions and crystallizations. Mark now,
however, that the reverse is the case when the salts contained in the
same body of water are chemically homologous. The nitrates of baryta and
lead, or the sulphates of zinc, soda, and magnesia, unite in the same
crystals; nor will they crystallize separately if these crystals be
dissolved afresh, and afresh crystallized, even with great care. On
seeking the cause of this anomaly, chemists found that such salts were
isomorphous—that their atoms, though not chemically identical, were
identical in the proportions of acid, base, and water, composing them,
and in their crystalline forms: whence it was inferred that their atoms
are nearly alike in structure. Thus is clearly illustrated the truth,
that units of unlike kinds are differentiated and integrated with a
readiness proportionate to the degree of their unlikeness. In the first
case we see that being dissimilar in their forms, but similar in so far
as they are soluble in water of a certain temperature, the atoms
segregate, though imperfectly. In the second case we see that the atoms,
having not only the likeness implied by solubility in the same
menstruum, but also a great likeness of structure, do not segregate—are
differentiated and integrated only under quite special conditions, and
then very incompletely. That is, the incident force of mutual polarity
impresses unlike motions on the mixed units in proportion as they are
unlike; and therefore, in proportion as they are unlike, tends to
deposit them in separate places.
There is a converse cause of segregation, which it is needless here to
treat of with equal fulness. If different units acted on by the same
force, must be differently moved; so, too, must units of the same kind
be differently moved by different forces. Supposing some group of units
forming part of a homogeneous aggregate, are unitedly exposed to a force
that is unlike in amount or direction to the force acting on the rest of
the aggregate; then this group of units will separate from the rest,
provided that, of the force so acting on it, there remains any portion
not dissipated in molecular vibrations, nor absorbed in producing
molecular re-arrangements. After all that has been said above, this
proposition needs no defence.
Before ending our preliminary exposition, a complementary truth must be
specified; namely, that mixed forces are segregated by the reaction of
uniform matters, just as mixed matters are segregated by the action of
uniform forces. Of this truth a complete and sufficient illustration is
furnished by the dispersion of refracted light. A beam of light, made up
of ethereal undulations of different orders, is not uniformly deflected
by a homogeneous refracting body; but the different orders of
undulations it contains, are deflected at different angles: the result
being that these different orders of undulations are separated and
integrated, and so produce what we know as the colours of the spectrum.
A segregation of another kind occurs when rays of light traverse an
obstructing medium. Those rays which consist of comparatively short
undulations, are absorbed before those which consist of comparatively
long ones; and the red rays, which consist of the longest undulations,
alone penetrate when the obstruction is very great. How, conversely,
there is produced a separation of like forces by the reaction of unlike
matters, is also made manifest by the phenomena of refraction: since
adjacent and parallel beams of light, falling on, and passing through,
unlike substances, are made to diverge.
* * * * *
§ 124. On the assumption of their nebular origin, stars and planets
exemplify that cause of material integration last assigned—the action of
unlike forces on like units.
In a preceding chapter (§ 110) we saw that if matter ever existed in a
diffused form, it could not continue uniformly distributed, but must
break up into masses. It was shown that in the absence of a perfect
balance of mutual attractions among atoms dispersed through unlimited
space, there must arise breeches of continuity throughout the aggregate
formed by them, and a concentration of it towards centres of dominant
attraction. Where any such breech of continuity occurs, and the atoms
that were before adjacent separate from each other; they do so in
consequence of a difference in the forces to which they are respectively
subject. The atoms on the one side of the breech are exposed to a
certain surplus attraction in the direction in which they begin to move;
and those on the other to a surplus attraction in the opposite
direction. That is, the adjacent groups of like units are exposed to
unlike resultant forces; and accordingly separate and integrate.
The formation and detachment of a nebulous ring, illustrates the same
general principle. To conclude, as Laplace did, that the equatorial
portion of a rotating nebulous spheroid, will, during concentration,
acquire a centrifugal force sufficient to prevent it from following the
rest of the contracting mass, is to conclude that such portions will
remain behind as are in common subject to a certain differential force.
The line of division between the ring and the spheroid, must be a line
inside of which the aggregative force is greater than the force
resisting aggregation; and outside of which the force resisting
aggregation is greater than the aggregative force. Hence the alleged
process conforms to the law that among like units, separation and
integration is produced by the action of unlike forces.
Astronomical phenomena do not furnish any other than these hypothetical
examples. In its present comparatively settled condition, the Solar
System exhibits no direct evidence of progressing integration: unless
indeed under the insignificant form of the union of meteoric masses with
the Earth, and, occasionally perhaps, of cometary matter with the Sun.
* * * * *
§ 125. Those geologic changes usually classed as aqueous, display under
numerous forms the segregation of unlike units by a uniform incident
force. On sea-shores, the waves are ever sorting-out and separating the
mixed materials against which they break. From each mass of fallen
cliff, the rising and ebbing tide carries away all those particles which
are so small as to remain long suspended in the water; and, at some
distance from shore, deposits them in the shape of fine sediment. Large
particles, sinking with comparative rapidity, are accumulated into beds
of sand near low water-mark. The coarse grit and small pebbles collect
together on the incline up which the breakers rush. And on the top lie
the larger stones and boulders. Still more specific segregations may
occasionally be observed. Flat pebbles, produced by the breaking down of
laminated rock, are sometimes separately collected in one part of a
shingle bank. On this shore the deposit is wholly of mud; on that it is
wholly of sand. Here we find a sheltered cove filled with small pebbles
almost of one size; and there, in a curved bay one end of which is more
exposed than the other, we see a progressive increase in the massiveness
of the stones as we walk from the less exposed to the more exposed end.
Indeed, our sedimentary strata form one vast series of illustrations of
the alleged law. Trace the history of each deposit, and we are quickly
led down to the fact, that mixed fragments of matter, differing in their
sizes or weights, are, when exposed to the momentum and friction of
water, joined with the attraction of the Earth, selected from each
other, and united into groups of comparatively like fragments. We see
that, other things equal, the separation is definite in proportion as
the differences of the units are marked; and that, under the action of
the same aggregate of forces, the most widely unlike units are most
widely removed from each other.
Among igneous changes we do not find so many examples of the process
described. When specifying the conditions to Evolution, it was pointed
out (§ 104) that molecular vibration exceeding a certain intensity, does
not permit those integrations which result from the action of minor
differential forces. Nevertheless, geological phenomena of this order
are not barren of illustrations. Where the mixed matters composing the
Earth’s crust have been raised to a very high temperature, segregation
habitually takes place as the temperature diminishes. Sundry of the
substances that escape in a gaseous form from volcanoes, sublime into
crystals on coming against cool surfaces; and solidifying, as these
substances do, at different temperatures, they are deposited at
different parts of the crevices through which they are emitted together.
The best illustration, however, is furnished by the changes that occur
during the slow cooling of igneous rock. When, through one of the
fractures from time to time made in the solid shell which forms the
Earth’s crust, a portion of the molten nucleus is extruded; and when
this is cooled with comparative rapidity, through free radiation and
contact with cold masses; it forms a substance known as trap or basalt—a
substance that is uniform in texture, though made up of various
ingredients. But when, not escaping through the superficial strata, such
a portion of the molten nucleus is slowly cooled, it becomes what we
know as granite: the mingled particles of quartz, feldspar, and mica,
being kept for a long time in a fluid and semi-fluid state—a state of
comparative mobility—undergo those changes of position which the forces
impressed on them by their fellow units necessitate. Having time in
which to generate the requisite motions of the atoms, the differential
forces arising from mutual polarity, segregate the quartz, feldspar, and
mica, into crystals. How completely this is dependent on the
long-continued agitation of the mixed particles, and consequent
long-continued mobility by small differential forces, is proved by the
fact that in granite dykes, the crystals in the centre of the mass,
where the fluidity or semi-fluidity continued for a longer time, are
much larger than those at the sides, where contact with the neighbouring
rock caused more rapid cooling and solidification.
* * * * *
§ 126. The actions going on throughout an organism are so involved and
subtle, that we cannot expect to identify the particular forces by which
particular integrations are effected. Among the few instances admitting
of tolerably definite interpretation, the best are those in which
mechanical pressures and tensions are the agencies at work. We shall
discover several on studying the bony frame of the higher animals.
The vertebral column of a man, is subject, as a whole, to certain
general strains—the weight of the body, together with the reactions
involved by all considerable muscular efforts; and in conformity with
this, it has a certain general integration. At the same time, being
exposed to different forces in the course of those lateral bendings
which the movements necessitate, its parts retain a certain
separateness. And if we trace up the development of the vertebral column
from its primitive form of a cartilaginous cord in the lowest fishes, we
see that, throughout, it maintains an integration corresponding to the
unity of the incident forces, joined with a division into segments
corresponding to the variety of the incident forces. Each segment,
considered apart, exemplifies the truth more simply. A vertebra is not a
single bone, but consists of a central mass with sundry appendages or
processes; and in rudimentary types of vertebræ, those appendages are
quite separate from the central mass, and, indeed, exist before it makes
its appearance. But these several independent bones, constituting a
primitive spinal segment, are subject to a certain aggregate of forces
which agree more than they differ: as the fulcrum to a group of muscles
habitually acting together, they perpetually undergo certain reactions
in common. And accordingly, we see that in the course of development
they gradually coalesce. Still clearer is the illustration
furnished by spinal segments that become fused together where they are
together exposed to some predominant strain. The sacrum consists of a
group of vertebræ firmly united. In the ostrich and its congeners there
are from seventeen to twenty sacral vertebræ; and besides being
confluent with each other, these are confluent with the iliac bones,
which run on each side of them. If now we assume these vertebræ to have
been originally separate, as they still are in the embryo bird; and if
we consider the mechanical conditions to which they must in such case
have been exposed; we shall see that their union results in the alleged
way. For through these vertebræ the entire weight of the body is
transferred to the legs: the legs support the pelvic arch; the pelvic
arch supports the sacrum; and to the sacrum is articulated the rest of
the spine, with all the limbs and organs attached to it. Hence, if
separate, the sacral vertebræ must be held firmly together by
strongly-contracted muscles; and must, by implication, be prevented from
partaking in those lateral movements which the other vertebræ
undergo—they must be subject to a common strain, while they are
preserved from strains which would affect them differently; and so they
fulfil the conditions under which integration occurs. But the
cases in which cause and effect are brought into the most obvious
relation, are supplied by the limbs. The metacarpal bones (those which
in man support the palm of the hand) are separate from each other in the
majority of mammalia: the separate actions of the toes entailing on them
slight amounts of separate movements. This is not so however in the
ox-tribe and the horse-tribe. In the ox-tribe, only the middle
metacarpals (third and fourth) are developed; and these, attaining
massive proportions, coalesce to form the cannon bone. In the
horse-tribe, the integration is what we may distinguish as indirect: the
second and fourth metacarpals are present only as rudiments united to
the sides of the third, while the third is immensely developed; thus
forming a cannon bone which differs from that of the ox in being a
single cylinder, instead of two cylinders fused together. The metatarsus
in these quadrupeds exhibits parallel changes. Now each of these
metamorphoses occurs where the different bones grouped together have no
longer any different functions, but retain only a common function. The
feet of oxen and horses are used solely for locomotion—are not put like
those of unguiculate mammals to purposes which involve some relative
movements of the metacarpals. Thus there directly or indirectly results
a single mass of bone where the incident force is single. And for the
inference that these facts have a causal connexion, we find confirmation
throughout the entire class of birds; in the wings and legs of which,
like integrations are found under like conditions. While this
sheet is passing through the press, a fact illustrating this general
truth in a yet more remarkable manner, has been mentioned to me by Prof.
Huxley; who kindly allows me to make use of it while still unpublished
by him. The _Glyptodon_, an extinct mammal found fossilized in South
America, has long been known as a large uncouth creature allied to the
Armadillo, but having a massive dermal armour consisting of polygonal
plates closely fitted together so as to make a vast box, inclosing the
body in such way as effectually to prevent it from being bent, laterally
or vertically, in the slightest degree. This bony box, which must have
weighed several hundred-weight, was supported on the spinous processes
of the vertebræ, and on the adjacent bones of the pelvic and thoracic
arches. And the significant fact now to be noted, is, that here, where
the trunk vertebræ were together exposed to the pressure of this heavy
dermal armour, at the same time that, by its rigidity, they were
preserved from all relative movements, the entire series of them were
united into one solid, continuous bone.
The formation and maintenance of a species, considered as an assemblage
of similar organisms, is interpretable in an analogous way. We have
already seen that in so far as the members of a species are subject to
different sets of incident forces, they are differentiated, or divided
into varieties. And here it remains to add that in so far as they are
subject to like sets of incident forces, they are integrated, or reduced
to, and kept in, the state of a uniform aggregate. For by the process of
“natural selection,” there is a continual purification of each species
from those individuals which depart from the common type in ways that
unfit them for the conditions of their existence. Consequently, there is
a continual leaving behind of those individuals which are in all
respects fit for the conditions of their existence; and are therefore
very nearly alike. The circumstances to which any species is exposed,
being, as we before saw, an involved combination of incident forces; and
the members of the species having mixed with them some that differ more
than usual from the average structure required for meeting these forces;
it results that these forces are constantly separating such divergent
individuals from the rest, and so preserving the uniformity of the
rest—keeping up its integrity as a species. Just as the changing autumn
leaves are picked out by the wind from among the green ones around them,
or just as, to use Prof. Huxley’s simile, the smaller fragments pass
through the sieve while the larger are kept back; so, the uniform
incidence of external forces affects the members of a group of organisms
similarly in proportion as they are similar, and differently in
proportion as they are different; and thus is ever segregating the like
by parting the unlike from them. Whether these separated members are
killed off, as mostly happens, or whether, as otherwise happens, they
survive and multiply into a distinct variety, in consequence of their
fitness to certain partially unlike conditions, matters not to the
argument. The one case conforms to the law, that the unlike units of an
aggregate are differentiated and integrated when uniformly subject to
the same incident forces; and the other to the converse law, that the
like units of an aggregate are differentiated and integrated when
subject to different incident forces. And on consulting Mr. Darwin’s
remarks on divergence of character, it will be seen that the
segregations thus caused tend ever to become more definite.
* * * * *
§ 127. Mental evolution under one of its leading aspects, we found to
consist in the formation of groups of like objects and like
relations—a differentiation of the various things originally
confounded together in one assemblage, and an integration of each
separate order of things into a separate group (§ 113). Here it
remains to point out that while unlikeness in the incident forces is
the cause of such differentiations, likeness in the incident forces is
the cause of such integrations. For what is the process through which
classifications are established? At first, in common with the
uninitiated, the botanist recognizes only such conventional divisions
as those which agriculture has established—distinguishes a few
vegetables and cereals, and groups the rest together into the one
miscellaneous aggregate of wild plants. How do these wild plants
become grouped in his mind into orders, genera, and species? Each
plant he examines yields him a certain complex impression. Every now
and then he picks up a plant like one before seen; and the recognition
of it is the production in him of a like connected group of
sensations, by a like connected group of attributes. That is to say,
there is produced throughout the nerves concerned, a combined set of
changes, similar to a combined set of changes before produced.
Considered analytically, each such combined set of changes is a
combined set of molecular modifications wrought in the affected part
of the organism. On every repetition of the impression, a like
combined set of molecular modifications is superposed on the previous
ones, and makes them greater: thus generating an internal idea
corresponding to these similar external objects. Meanwhile, another
kind of plant produces in the brain of the botanist another set of
combined changes or molecular modifications—a set which does not agree
with and deepen the one we have been considering, but disagrees with
it; and by repetition of such there is generated a different idea
answering to a different species. What now is the nature of this
process expressed in general terms? On the one hand there are the like
and unlike things from which severally emanate the groups of forces by
which we perceive them. On the other hand, there are the organs of
sense and percipient centres, through which, in the course of
observation, these groups of forces pass. In passing through these
organs of sense and percipient centres, the like groups of forces are
segregated, or separated from the unlike groups of forces; and each
such differentiated and integrated series of groups of forces,
answering to an external genus or species, constitutes a state of
consciousness which we call our idea of the genus or species. We
before saw that as well as a separation of mixed matters by the same
force, there is a separation of mixed forces by the same matter; and
here we may further see that the unlike forces so separated, work
unlike structural changes in the aggregate that separates
them—structural changes each of which thus represents, and is
equivalent to, the integrated series of motions that has produced it.
By a parallel process, the connexions of co-existence and sequence among
impressions, become differentiated and integrated simultaneously with
the impressions themselves. When two phenomena that have been
experienced in a given order, are repeated in the same order, those
nerves which before were affected by the transition are again affected;
and such molecular modification as they received from the first motion
propagated through them, is increased by this second motion along the
same route. Each such motion works a structural alteration, which, in
conformity with the general law set forth in Chapter X., involves a
diminution of the resistance to all such motions that afterwards occur.
The integration of these successive motions (or more strictly, the
permanently effective portions of them expended in overcoming
resistance) thus becomes the cause of, and the measure of, the mental
connexion between the impressions which the phenomena produce.
Meanwhile, phenomena that are recognized as different from these, being
phenomena that therefore affect different nervous elements, will have
their connexions severally represented by motions along other routes;
and along each of these other routes, the nervous discharges will
severally take place with a readiness proportionate to the frequency
with which experience repeats the connexion of phenomena. The
classification of relations must hence go on _pari passu_ with the
classification of the related things. In common with the mixed
sensations received from the external world, the mixed relations it
presents, cannot be impressed on the organism without more or less
segregation of them resulting. And through this continuous
differentiation and integration of changes or motions, which constitutes
nervous function, there is gradually wrought that differentiation and
integration of matter, which constitutes nervous structure.
* * * * *
§ 128. In social evolution, the collecting together of the like and the
separation of the unlike, by incident forces, is primarily displayed in
the same manner as we saw it to be among groups of inferior creatures.
The human races tend to differentiate and integrate, as do races of
other living forms. Of the forces which effect and maintain the
segregations of mankind, may first be named those external ones which we
class as physical conditions. The climate and food that are favourable
to an indigenous people, are more or less detrimental to a people of
different bodily constitution, coming from a remote part of the Earth.
In tropical regions the northern races cannot permanently exist: if not
killed off in the first generation, they are so in the second; and, as
in India, can maintain their footing only by the artificial process of
continuous immigration and emigration. That is to say, the external
forces acting equally on the inhabitants of a given locality, tend to
expel all who are not of a certain type; and so to keep up the
integration of those who are of that type. Though elsewhere, as among
European nations, we see a certain amount of permanent intermixture,
otherwise brought about, we still see that this takes place between
races of not very different types, that are naturalized to not very
different conditions. The other forces conspiring to produce these
national integrations, are those mental ones which show themselves in
the affinities of men for others like themselves. Emigrants usually
desire to get back among their own people; and where their desire does
not take effect, it is only because the restraining ties are too great.
Units of one society who are obliged to reside in another, very
generally form colonies in the midst of that other—small societies of
their own. Races which have been artificially severed, show strong
tendencies to re-unite. Now though these integrations that result from
the mutual affinities of kindred men, do not seem interpretable as
illustrations of the general principle above enunciated, they really are
thus interpretable. When treating of the direction of motion (§ 91), it
was shown that the actions performed by men for the satisfaction of
their wants, were always motions along lines of least resistance. The
feelings characterizing a member of a given race, are feelings which get
complete satisfaction only among other members of that race—a
satisfaction partly derived from sympathy with those having like
feelings, but mainly derived from the adapted social conditions which
grow up where such feelings prevail. When, therefore, a citizen of any
nation is, as we see, attracted towards others of his nation, the
rationale is, that certain agencies which we call desires, move him in
the direction of least resistance. Human motions, like all other
motions, being determined by the distribution of forces, it follows that
such integrations of races as are not produced by incident external
forces, are produced by forces which the units of the races exercise on
each other.
During the development of each society, we see analogous segregations
caused in analogous ways. A few of them result from minor natural
affinities; but those most important ones which constitute political and
industrial organization, result from the union of men in whom
similarities have been produced by education—using education in its
widest sense, as comprehending all processes by which citizens are
moulded to special functions. Men brought up to bodily labour, are men
who have had wrought in them a certain likeness—a likeness which, in
respect of their powers of action, obscures and subordinates their
natural differences. Those trained to brain-work, have acquired a
certain other community of character which makes them, as social units,
more like each other than like those trained to manual occupations. And
there arise class-integrations answering to these superinduced
likenesses. Much more definite integrations take place among the much
more definitely assimilated members of any class who are brought up to
the same calling. Even where the necessities of their work forbid
concentration in one locality, as among artizans happens with masons and
brick-layers, and among traders happens with the retail distributors,
and among professionals happens with the medical men; there are not
wanting Operative Builders Unions, and Grocers Societies, and Medical
Associations, to show that these artificially-assimilated citizens
become integrated as much as the conditions permit. And where, as among
the manufacturing classes, the functions discharged do not require the
dispersion of the citizens thus artificially assimilated, there is a
progressive aggregation of them in special localities; and a consequent
increase in the definiteness of the industrial divisions. If now
we seek the causes of these integrations, considered as results of force
and motion, we find ourselves brought to the same general principle as
before. This likeness generated in any class or subclass by training, is
an aptitude acquired by its members for satisfying their wants in like
ways. That is, the occupation to which each man has been brought up, has
become to him, in common with those similarly brought up, a line of
least resistance. Hence under that pressure which determines all men to
activity, these similarly-modified social units are similarly affected,
and tend to take similar courses. If then there be any locality which,
either by its physical peculiarities or by peculiarities wrought on it
during social evolution, is rendered a place where a certain kind of
industrial action meets with less resistance than elsewhere; it follows
from the law of direction of motion that those social units who have
been moulded to this kind of industrial action, will move towards this
place, or become integrated there. If, for instance, the proximity of
coal and iron mines to a navigable river, gives to Glasgow a certain
advantage in the building of iron ships—if the total labour required to
produce the same vessel, and get its equivalent in food and clothing, is
less there than elsewhere; a concentration of iron-ship builders is
produced at Glasgow: either by keeping there the population born to
iron-ship building; or by immigration of those elsewhere engaged in it;
or by both—a concentration that would be still more marked did not other
districts offer counter-balancing facilities. The principle equally
holds where the occupation is mercantile instead of manufacturing.
Stock-brokers cluster together in the city, because the amount of effort
to be severally gone through by them in discharging their functions, and
obtaining their profits, is less there than in other localities. A place
of exchange having once been established, becomes a place where the
resistance to be overcome by each is less than elsewhere; and the
pursuit of the course of least resistance by each, involves their
aggregation around this place.
Of course, with units so complicated as those which constitute a
society, and with forces so involved as those which move them, the
resulting differentiations and integrations must be far more entangled,
or far less definite, than those we have hitherto considered. But though
there may be pointed out many anomalies which at first sight seem
inconsistent with the alleged law, a closer study shows that they are
but subtler illustrations of it. For men’s likenesses being of various
kinds, lead to various order of integration. There are likenesses of
disposition, likenesses of taste, likenesses produced by intellectual
culture, likenesses that result from class-training, likenesses of
political feeling; and it needs but to glance round at the
caste-divisions, the associations for philanthropic, scientific, and
artistic purposes, the religious parties and social cliques; to see that
some species of likeness among the component members of each body
determines their union. Now these different integrations, by traversing
each other, and often by their indirect antagonism, more or less obscure
each other; and prevent any one kind of integration from becoming
complete. Hence the anomalies referred to. But if this cause of
incompleteness be duly borne in mind, social segregations will be seen
to conform entirely to the same principle as all other segregations.
Analysis will show that either by external incident forces, or by what
we may in a sense regard as mutual polarity, there are ever being
produced in society integrations of those units which have either a
natural likeness or a likeness generated by training.
* * * * *
§ 129. Can the general truth thus variously illustrated be deduced from
the persistence of force, in common with foregoing ones? Probably the
exposition at the beginning of the chapter will have led most readers to
conclude that it can be so deduced.
The abstract propositions involved are these:—First, that like units,
subject to a uniform force capable of producing motion in them, will be
moved to like degrees in the same direction. Second, that like units if
exposed to unlike forces capable of producing motion in them, will be
differently moved—moved either in different directions or to different
degrees in the same direction. Third, that unlike units if acted on by a
uniform force capable of producing motion in them, will be differently
moved—moved either in different directions or to different degrees in
the same direction. Fourth, that the incident forces themselves must be
affected in analogous ways: like forces falling on like units must be
similarly modified by the conflict; unlike forces falling on like units
must be dissimilarly modified; and like forces falling on unlike units
must be dissimilarly modified. These propositions admit of reduction to
a still more abstract form. They all of them amount to this:—that in the
actions and reactions of force and matter, an unlikeness in either of
the factors necessitates an unlikeness in the effects; and that in the
absence of unlikeness in either of the factors the effects must be
alike.
When thus generalized, the immediate dependence of these propositions on
the persistence of force, becomes obvious. Any two forces that are not
alike, are forces which differ either in their amounts or directions or
both; and by what mathematicians call the resolution of forces, it may
be proved that this difference is constituted by the presence in the one
of some force not present in the other. Similarly, any two units or
portions of matter which are unlike in size, weight, form, or other
attribute, can be known by us as unlike only through some unlikeness in
the forces they impress on our consciousness; and hence this unlikeness
also, is constituted by the presence in the one of some force or forces
not present in the other. Such being the common nature of these
unlikenesses, what is the inevitable corollary? Any unlikeness in the
incident forces, where the things acted on are alike, must generate a
difference between the effects; since otherwise, the differential force
produces no effect, and force is not persistent. Any unlikeness in the
things acted on, where the incident forces are alike, must generate a
difference between the effects; since otherwise, the differential force
whereby these things are made unlike, produces no effect, and force is
not persistent. While, conversely, if the forces acting and the things
acted on, are alike, the effects must be alike; since otherwise, a
differential effect can be produced without a differential cause, and
force is not persistent.
Thus these general truths being necessary implications of the
persistence of force, all the re-distributions above traced out as
characterizing Evolution in its various phases, are also implications of
the persistence of force. Such portions of the permanently effective
forces acting on any aggregate, as produce sensible motions in its
parts, cannot but work the segregations which we see take place. If of
the mixed units making up such aggregate, those of the same kind have
like motions impressed on them by a uniform force, while units of
another kind are moved by this uniform force in ways more or less unlike
the ways in which those of the first kind are moved, the two kinds must
separate and integrate. If the units are alike and the forces unlike, a
division of the differently affected units is equally necessitated. Thus
there inevitably arises the demarcated grouping which we everywhere see.
By virtue of this segregation that grows ever more decided while there
remains any possibility of increasing it, the change from uniformity to
multiformity is accompanied by a change from indistinctness in the
relations of parts to distinctness in the relations of parts. As we
before saw that the transformation of the homogeneous into the
heterogeneous is inferrable from that ultimate truth which transcends
proof; so we here see, that from this same truth is inferrable the
transformation of an indefinite homogeneity into a definite
heterogeneity.