which remain inexplicable in the absence of this factor. If, as we see,
co-operative parts do not vary together, even when few and close
together, and may not therefore be assumed to do so when many and
remote, we cannot account for those innumerable changes in organization
which are implied when, for advantageous use of some modified part, many
other parts which join it in action have to be modified.
Further, as increasing complexity of structure, accompanying increasing
complexity of life, implies increasing number of faculties, of which
each one conduces to preservation of self or descendants; and as the
various individuals of a species, severally requiring something like the
normal amounts of all these, may individually profit, here by an unusual
amount of one, and there by an unusual amount of another; it follows
that as the number of faculties becomes greater, it becomes more
difficult for any one to be further developed by natural selection. Only
where increase of some one is _predominantly_ advantageous does the
means seem adequate to the end. Especially in the case of powers which
do not subserve self-preservation in appreciable degrees, does
development by natural selection appear impracticable.
It is a fact recognized by Mr. Darwin, that where, by selection through
successive generations, a part has been increased or decreased, its
reaction upon other parts entails changes in them. This reaction is
effected through the changes of function involved. If the changes of
structure produced by such changes of function, are inheritable, then
the re-adjustment of parts throughout the organism, taking place
generation after generation, maintains an approximate balance; but if
not, then generation after generation the organism must get more and
more out of gear, and tend to become unworkable.
Further, as it is proved that change in the balance of functions
registers its effects on the reproductive elements, we have to choose
between the alternatives that the registered effects are irrelevant to
the particular modifications which the organism has undergone, or that
they are such as tend to produce repetitions of these modifications. The
last of these alternatives makes the facts comprehensible; but the first
of them not only leaves us with several unsolved problems, but is
incongruous with the general truth that by reproduction, ancestral
traits, down to minute details, are transmitted.
Though, in the absence of pecuniary interests and the interests in
hobbies, no such special experiments as those which have established the
inheritance of fortuitous variations have been made to ascertain whether
functionally-produced modifications are inherited; yet certain apparent
instances of such inheritance have forced themselves on observation
without being sought for. In addition to other indications of a less
conspicuous kind, is the one I have given above—the fact that the
apparatus for tearing and mastication has decreased with decrease of its
function, alike in civilized man and in some varieties of dogs which
lead protected and pampered lives. Of the numerous cases named by Mr.
Darwin, it is observable that they are yielded not by one class of parts
only, but by most if not all classes—by the dermal system, the muscular
system, the osseous system, the nervous system, the viscera; and that
among parts liable to be functionally modified, the most numerous
observed cases of inheritance are furnished by those which admit of
preservation and easy comparison—the bones: these cases, moreover, being
specially significant as showing how, in sundry unallied species,
parallel changes of structure have occurred along with parallel changes
of habit.
What, then, shall we say of the general implication? Are we to stop
short with the admission that inheritance of functionally-produced
modifications takes place only in cases in which there is evidence of
it? May we properly assume that these many instances of changes of
structure caused by changes of function, occurring in various tissues
and various organs, are merely special and exceptional instances having
no general significance? Shall we suppose that though the evidence which
already exists has come to light without aid from a body of inquirers,
there would be no great increase were due attention devoted to the
collection of evidence? This is, I think, not a reasonable supposition.
To me the _ensemble_ of the facts suggests the belief, scarcely to be
resisted, that the inheritance of functionally-produced modifications
takes place universally. Looking at physiological phenomena as
conforming to physical principles, it is difficult to conceive that a
changed play of organic forces which in many cases of different kinds
produces an inherited change of structure, does not do this in all
cases. The implication, very strong I think, is that the action of every
organ produces on it a reaction which, usually not altering its rate of
nutrition, sometimes leaves it with diminished nutrition consequent on
diminished action, and at other times increases its nutrition in
proportion to its increased action; that while generating a modified
_consensus_ of functions and of structures, the activities are at the
same time impressing this modified _consensus_ on the sperm-cells and
germ-cells whence future individuals are to be produced; and that in
ways mostly too small to be identified, but occasionally in more
conspicuous ways and in the course of generations, the resulting
modifications of one or other kind show themselves. Further, it seems to
me that as there are certain extensive classes of phenomena which are
inexplicable if we assume the inheritance of fortuitous variations to be
the sole factor, but which become at once explicable if we admit the
inheritance of functionally-produced changes, we are justified in
concluding that this inheritance of functionally-produced changes has
been not simply a co-operating factor in organic evolution, but has been
a co-operating factor without which organic evolution, in its higher
forms at any rate, could never have taken place.
Be this or be it not a warrantable conclusion, there is, I think, good
reason for a provisional acceptance of the hypothesis that the effects
of use and disuse are inheritable; and for a methodic pursuit of
inquiries with the view of either establishing it or disproving it. It
seems scarcely reasonable to accept without clear demonstration, the
belief that while a trivial difference of structure arising
spontaneously is transmissible, a massive difference of structure,
maintained generation after generation by change of function, leaves no
trace in posterity. Considering that unquestionably the modification of
structure by function is a _vera causa_, in so far as concerns the
individual; and considering the number of facts which so competent an
observer as Mr. Darwin regarded as evidence that transmission of such
modifications takes place in particular cases; the hypothesis that such
transmission takes place in conformity with a general law, holding of
all active structures, should, I think, be regarded as at least a good
working hypothesis.
* * * * *
But now supposing the broad conclusion above drawn to be
granted—supposing all to agree that from the beginning, along with
inheritance of useful variations fortuitously arising, there has been
inheritance of effects produced by use and disuse; do there remain no
classes of organic phenomena unaccounted for? To this question I think
it must be replied that there do remain classes of organic phenomena
unaccounted for. It may, I believe, be shown that certain cardinal
traits of animals and plants at large are still unexplained; and that a
further factor must be recognized. To show this, however, will require
another paper.
-----
Footnote 1:
It is probable that this shortening has resulted not directly but
indirectly, from the selection of individuals which were noted for
tenacity of hold; for the bull-dog's peculiarity in this respect seems
due to relative shortness of the upper jaw, giving the underhung
structure which, involving retreat of the nostrils, enables the dog to
continue breathing while holding.
II.
Ask a plumber who is repairing your pump, how the water is raised in it,
and he replies—“By suction.” Recalling the ability which he has to suck
up water into his mouth through a tube, he is certain that he
understands the pump's action. To inquire what he means by suction,
seems to him absurd. He says you know as well as he does, what he means;
and he cannot see that there is any need for asking how it happens that
the water rises in the tube when he strains his mouth in a particular
way. To the question why the pump, acting by suction, will not make the
water rise above 32 feet, and practically not so much, he can give no
answer; but this does not shake his confidence in his explanation.
On the other hand an inquirer who insists on knowing what suction is,
may obtain from the physicist answers which give him clear ideas, not
only about it but about many other things. He learns that on ourselves
and all things around, there is an atmospheric pressure amounting to
about 15 pounds on the square inch: 15 pounds being the average weight
of a column of air having a square inch for its base and extending
upwards from the sea-level to the limit of the Earth's atmosphere. He is
made to observe that when he puts one end of a tube into water and the
other end into his mouth, and then draws back his tongue, so leaving a
vacant space, two things happen. One is that the pressure of air outside
his cheeks, no longer balanced by an equal pressure of air inside,
thrusts his cheeks inwards; and the other is that the pressure of air on
the surface of the water, no longer balanced by an equal pressure of air
within the tube and his mouth (into which part of the air from the tube
has gone) the water is forced up the tube in consequence of the unequal
pressure. Once understanding thus the nature of the so-called suction,
he sees how it happens that when the plunger of the pump is raised and
relieves from atmospheric pressure the water below it, the atmospheric
pressure on the water in the well, not being balanced by that on the
water in the tube, forces the water higher up the tube, so that it
follows the plunger. And now he sees why the water cannot be raised
beyond the theoretic limit of 32 feet: a limit made much lower in
practice by imperfections in the apparatus. For if, simplifying the
conception, he supposes the tube of the pump to be a square inch in
section, then the atmospheric pressure of 15 pounds per square inch on
the water in the well, can raise the water in the tube to such height
only that the entire column of it weighs 15 pounds. Having been thus
enlightened about the pump's action, the action of a barometer becomes
intelligible. He perceives how, under the conditions established, the
weight of the column of mercury balances that of an atmospheric column
of equal diameter; and how, as the weight of the atmospheric column
varies, there is a corresponding variation in the weight of the
mercurial column,—shown by change of height. Moreover, having previously
supposed that he understood the ascent of a balloon when he ascribed it
to relative lightness, he now sees that he did not truly understand it.
For he did not recognize it as a result of that upward pressure caused
by the difference between the weight of the mass formed by the gas in
the balloon _plus_ the cylindrical column of air extending above it to
the limit of the atmosphere, and the weight of a similar cylindrical
column of air extending down to the under surface of the balloon: this
difference of weight causing an equivalent upward pressure on the under
surface.
Why do I introduce these familiar truths so entirely irrelevant to my
subject? I do it to show, in the first place, the contrast between a
vague conception of a cause and a distinct conception of it; or rather,
the contrast between that conception of a cause which results when it is
simply classed with some other or others which familiarity makes us
think we understand, and that conception of a cause which results when
it is represented in terms of definite physical forces admitting of
measurement. And I do it to show, in the second place, that when we
insist on resolving a verbally-intelligible cause into its actual
factors, we get not only a clear solution of the problem before us, but
we find that the way is opened to solutions of sundry other problems.
While we rest satisfied with unanalyzed causes, we may be sure both that
we do not rightly comprehend the production of the particular effects
ascribed to them, and that we overlook other effects which would be
revealed to us by contemplation of the causes as analyzed. Especially
must this be so where the causation is complex. Hence we may infer that
the phenomena presented by the development of species, are not likely to
be truly conceived unless we keep in view the concrete agencies at work.
Let us look closely at the facts to be dealt with.
* * * * *
The growth of a thing is effected by the joint operation of certain
forces on certain materials; and when it dwindles, there is either a
lack of some materials, or the forces co-operate in a way different from
that which produces growth. If a structure has varied, the implication
is that the processes which built it up were made unlike the parallel
processes in other cases, by the greater or less amount of some one or
more of the matters or actions concerned. Where there is unusual
fertility, the play of vital activities is thereby shown to have
deviated from the ordinary play of vital activities; and conversely, if
there is infertility. If the germs, or ova, or seed, or offspring
partially developed, survive more or survive less, it is either because
their molar or molecular structures are unlike the average ones, or
because they are affected in unlike ways by surrounding agencies. When
life is prolonged, the fact implies that the combination of actions,
visible and invisible, constituting life, retains its equilibrium longer
than usual in presence of environing forces which tend to destroy its
equilibrium. That is to say, growth, variation, survival, death, if they
are to be reduced to the forms in which physical science can recognize
them, must be expressed as effects of agencies definitely
conceived—mechanical forces, light, heat, chemical affinity, &c.
This general conclusion brings with it the thought that the phrases
employed in discussing organic evolution, though convenient and indeed
needful, are liable to mislead us by veiling the actual agencies. That
which really goes on in every organism is the working together of
component parts in ways conducing to the continuance of their combined
actions, in presence of things and actions outside; some of which tend
to subserve, and others to destroy, the combination. The matters and
forces in these two groups, are the sole causes properly so called. The
words “natural selection,” do not express a cause in the physical sense.
They express a mode of co-operation among causes—or rather, to speak
strictly, they express an effect of this mode of co-operation. The idea
they convey seems perfectly intelligible. Natural selection having been
compared with artificial selection, and the analogy pointed out, there
apparently remains no indefiniteness: the inconvenience being, however,
that the definiteness is of a wrong kind. The tacitly implied Nature
which selects, is not an embodied agency analogous to the man who
selects artificially; and the selection is not the picking out of an
individual fixed on, but the overthrowing of many individuals by
agencies which one successfully resists, and hence continues to live and
multiply. Mr. Darwin was conscious of these misleading implications. In
the introduction to his _Animals and Plants under Domestication_ (p. 6)
he says:—
“For brevity sake I sometimes speak of natural selection as an
intelligent power; ... I have, also, often personified the word
Nature; for I have found it difficult to avoid this ambiguity; but I
mean by nature only the aggregate action and product of many natural
laws,—and by laws only the ascertained sequence of events.”
But while he thus clearly saw, and distinctly asserted, that the factors
of organic evolution are the concrete actions, inner and outer, to which
every organism is subject, Mr. Darwin, by habitually using the
convenient figure of speech, was, I think, prevented from recognizing so
fully as he would otherwise have done, certain fundamental consequences
of these actions.
Though it does not personalize the cause, and does not assimilate its
mode of working to a human mode of working, kindred objections may be
urged against the expression to which I was led when seeking to present
the phenomena in literal terms rather than metaphorical terms—the
survival of the fittest;[2] for in a vague way the first word, and in a
clear way the second word, calls up an anthropocentric idea. The thought
of survival inevitably suggests the human view of certain sets of
phenomena, rather than that character which they have simply as groups
of changes. If, asking what we really know of a plant, we exclude all
the ideas associated with the words life and death, we find that the
sole facts known to us are that there go on in the plant certain
inter-dependent processes, in presence of certain aiding and hindering
influences outside of it; and that in some cases a difference of
structure or a favourable set of circumstances, allows these
inter-dependent processes to go on for longer periods than in other
cases. Again, in the working together of those many actions, internal
and external, which determine the lives or deaths of organisms, we see
nothing to which the words fitness and unfitness are applicable in the
physical sense. If a key fits a lock, or a glove a hand, the relation of
the things to one another is presentable to the perceptions. No approach
to fitness of this kind is made by an organism which continues to live
under certain conditions. Neither the organic structures themselves, nor
their individual movements, nor those combined movements of certain
among them which constitute conduct, are related in any analogous way to
the things and actions in the environment. Evidently the word fittest,
as thus used, is a figure of speech; suggesting the fact that amid
surrounding actions, an organism characterized by the word has either a
greater ability than others of its kind to maintain the equilibrium of
its vital activities, or else has so much greater a power of
multiplication that though not longer lived than they, it continues to
live in posterity more persistently. And indeed, as we here see, the
word fittest has to cover cases in which there may be less ability than
usual to survive individually, but in which the defect is more than made
good by higher degrees of fertility.
I have elaborated this criticism with the intention of emphasizing the
need for studying the changes which have gone on, and are ever going on,
in organic bodies, from an exclusively physical point of view. On
contemplating the facts from this point of view, we become aware that,
besides those special effects of the co-operating forces which eventuate
in the longer survival of one individual than of others, and in the
consequent increase through generations, of some trait which furthered
its survival, many other effects are being wrought on each and all of
the individuals. Bodies of every class and quality, inorganic as well as
organic, are from instant to instant subject to the influences in their
environments; are from instant to instant being changed by these in ways
that are mostly inconspicuous; and are in course of time changed by them
in conspicuous ways. Living things in common with dead things, are, I
say, being thus perpetually acted upon and modified; and the changes
hence resulting, constitute an all-important part of those undergone in
the course of organic evolution. I do not mean to imply that changes of
this class pass entirely unrecognized; for, as we shall see, Mr. Darwin
takes cognizance of certain secondary and special ones. But the effects
which are not taken into account, are those primary and universal
effects which give certain fundamental characters to all organisms.
Contemplation of an analogy will best prepare the way for appreciation
of them, and of the relation they bear to those which at present
monopolize attention.
An observant rambler along shores, will, here and there, note places
where the sea has deposited things more or less similar, and separated
them from dissimilar things—will see shingle parted from sand; larger
stones sorted from smaller stones; and will occasionally discover
deposits of shells more or less worn by being rolled about. Sometimes
the pebbles or boulders composing the shingle at one end of a bay, he
will find much larger than those at the other: intermediate sizes,
having small average differences, occupying the space between the
extremes. An example occurs, if I remember rightly, some mile or two to
the west of Tenby; but the most remarkable and well-known example is
that afforded by the Chesil bank. Here, along a shore some sixteen miles
long, there is a gradual increase in the sizes of the stones; which,
being at one end but mere pebbles, are at the other end immense
boulders. In this case, then, the breakers and the undertow have
effected a selection—have at each place left behind those stones which
were too large to be readily moved, while taking away others small
enough to be moved easily. But now, if we contemplate exclusively this
selective action of the sea, we overlook certain important effects which
the sea simultaneously works. While the stones have been differently
acted upon in so far that some have been left here and some carried
there; they have been similarly acted upon in two allied, but
distinguishable, ways. By perpetually rolling them about and knocking
them one against another, the waves have so broken off their most
prominent parts as to produce in all of them more or less rounded forms;
and then, further, the mutual friction of the stones simultaneously
caused, has smoothed their surfaces. That is to say in general terms,
the actions of environing agencies, so far as they have operated
indiscriminately, have produced in the stones a certain unity of
character; at the same time that they have, by their differential
effects, separated them: the larger ones having withstood certain
violent actions which the smaller ones could not withstand.
Similarly with other assemblages of objects which are alike in their
primary traits but unlike in their secondary traits. When simultaneously
exposed to the same set of actions, some of these actions, rising to a
certain intensity, may be expected to work on particular members of the
assemblage changes which they cannot work in those which are markedly
unlike; while others of the actions will work in all of them similar
changes, because of the uniform relations between these actions and
certain attributes common to all members of the assemblage. Hence it is
inferable that on living organisms, which form an assemblage of this
kind, and are unceasingly exposed in common to the agencies composing
their inorganic environments, there must be wrought two such sets of
effects. There will result a universal likeness among them consequent on
the likeness of their respective relations to the matters and forces
around; and there will result, in some cases, the differences due to the
differential effects of these matters and forces, and in other cases,
the changes which, being life-sustaining or life-destroying, eventuate
in certain natural selections.