AS REGARDS HEREDITY
_Problems of Heredity--Physiological Units--A Digression--The
Germ-Cells--Transmission of Acquired
Characters--Inconceivability--A Priori Argument--Practical
Conclusion_
Heredity is the relation of genetic continuity which links generation to
generation. An inheritance is all that the organism is or has to start
with on its life-journey in virtue of the hereditary relation to parents
and ancestors. In all ordinary cases, the inheritance has its initial
material basis in the egg-cell and the sperm-cell which unite in
fertilisation at the beginning of a new life, and these two kinds of
germ-cells, which bear the maternal and the paternal contributions, have
their peculiar virtue of reproducing like from like, just because they
are the unchanged or very slightly changed cell-descendants of the
fertilised ova from which the parents arose. A bud or a cutting
separated off from a living creature--tiger-lily or potato, polyp or
worm--reproduces an entire organism like the parent, if the appropriate
nurture-conditions are available; and it can do so because it is a fair
sample of the parental organisation. Similarly a germ-cell or two
germ-cells in conjunction can develop into a creature like the parent or
parents, in virtue of being the condensed essence of the parental
organisation. And the germ-cell is this because of its direct
continuity through undifferentiating cell-divisions with the original
germ-cell from which the parental body developed.
Even in ancient times men pondered over the resemblances and differences
between children and their parents--for like only _tends_ to beget
like--and wondered as to the nature of the bond which links generation
to generation. But although the problems are old, the precise study of
them is altogether modern. The first great step towards clearness was
the formulation of the cell-theory by Schwann and Schleiden (1838-9), by
Goodsir and Virchow, which made it clear that all but the simplest
organisms are built up of cells or modifications of cells, and that the
individual life usually begins as a fertilised egg-cell which proceeds
by division and re-division, by differentiation and integration, to
develop a more or less complex "body." It has become gradually clear
that while the fertilised egg-cell gives rise to body-cells which become
specialised, it also gives rise to unspecialised descendant-cells, which
take no share in body-making, but become the germ-cells--the potential
starting-points of another generation. A second great step was the
accumulation of facts of inheritance showing that all sorts of qualities
innate or inborn in the parents, essential and trivial, normal and
abnormal, bodily and mental, may be transmitted to the offspring as part
of the organic heritage. A third great step was implied in the
acceptance which Darwin in particular won for the general idea of
descent, for it is hardly too much to say that the scientific study of
the problems of heredity began when it was recognised that heredity is a
fundamental condition of evolution.
_Problems of Heredity._--In regard to Heredity there are three large
problems which tower above the crowd of more detailed problems. The
_first_ is: In what way are the germ-cells peculiar, how do they differ
from ordinary cells, what gives them their unique reproductive power,
how do they come to be such marvellous units that their development
results in a new organism? Only two answers have been suggested: (1)
that the germ-cells become receptacles of representative samples from
the different parts of the body (the pangenetic theory), and (2) that
the germ-cells owe their unique character to the fact that they are,
along lines of undifferentiated cell-lineage, the direct descendants of
the fertilised ova of the parents (the theory of germinal continuity).
Thanks, largely, to Weismann, the second view has prevailed over the
first, for which there is little factual basis.
The _second_ large problem is as to the way in which it may be supposed
that the hereditary qualities are represented in the germ-cell. Is the
germ-cell an extremely complex chemical mixture without pre-formed
architecture, which, as it lives and grows, gradually gives rise to
heterogeneous elements, differentiating along diverse lines according to
their diverse relations to one another and to their surrounding
conditions? Or is it from the first a complex architecture, an intricate
organisation of a large number of items representing particular
qualities, a mosaic of inheritance-bearers?
The _third_ large problem is as to the modes in which the inheritance,
normally bi-parental, and in some sense always a mingling of ancestral
contributions, can express itself. Sometimes the expression is
one-sided, sometimes it is a blend. The mother may look out of one eye,
and the father out of another, or the grandfather may be re-incarnated.
By inter-breeding hybrids pure types may be got, _or_ reversions, _or_
"an epidemic of variations." This is the problem of the diverse modes of
hereditary transmission, which we know in some cases to be expressible
in a formula, such as Mendel's law or Galton's law, and for which we can
sometimes hazard a hypothetical physiological interpretation.
_Physiological Units._--To each of these three problems Spencer made a
contribution. He started with the legitimate and fertile hypothesis of
"physiological units"--the ultimate life-bearing elements, intermediate
between the chemical molecules and the cell. Just as the same kinds and
even the same number of atoms compose by different arrangements numerous
quite different chemical molecules, _e.g._ in the protein-group, so out
of similar molecules diversely grouped an immense variety of
"physiological units" may be evolved. Out of the same pieces of coloured
glass one may get in the kaleidoscope a very large number of distinct
patterns, so in the course of nature similar molecules, grouping
themselves differently, have formed a very large number of distinct
"physiological units." The grouping is not merely positional and static
as in the kaleidoscope; it is dynamic and vital. Since Spencer sketched
his idea in 1864 many biologists have thought of units intermediate
between the chemical molecules and the cell, and the number of different
names which have been bestowed upon them is extraordinary, each voyager
re-naming his discovery, ignorant of or ignoring those who had
previously sailed the same seas. This recognition of "physiological
units" was a natural step in analysis as soon as it began to be
recognised that the cell was a little world in itself, a "firm" with
many partners. While we cannot agree with Delage that "Spencer est le
vrai pere de la conception initiale," since Bruecke expressed the same
idea in 1861, Spencer's exposition in 1864 was quite independent, and it
has not found the recognition it deserved.
It should be noted that the "gemmules" which Darwin assumed in his
provisional hypothesis of pangenesis to be given off by the various
cells of the body, were supposed to be of innumerable unlike kinds,
whereas in Spencer's argument "the implication everywhere is that the
physiological units are all of one kind."
It is admitted that the molecules of a crystallisable substance have
more or less mysterious relations to one another--"polarities" as we
call them--which result in definite crystalline forms appearing in
definite conditions, with a certain amount of diversity as everyone may
see in snow-crystals, and as is more precisely known in the case of
certain substances which have several forms of crystallisation. But just
as chemical molecules have in virtue of their organisation (always
dynamic as well as static) certain prescribed modes of relating
themselves to others like themselves, and building up a beautiful
integrate, a crystal, so, as Spencer pointed out, the "physiological
units" have their "polarities," _i.e._ their inherent constitutional
tendencies to build up forms along with their fellows. Here we have two
useful suggestions, (1) that development is like an elaborate organic
crystallisation, only much more energetically dynamic, and (2) that the
big fact of heredity--that like tends to beget like--has its parallel in
the way in which a minute fragment of a crystal can in the appropriate
environment of a solution of the same substance build up a crystal like
the original form from which it was separated. Germ-cells are potential
samples of the organisation which is expressed in the parent, but
Spencer did not advance to the more distinctively modern position which
recognises that they are separated off rather from the fertilised ovum
which gave rise to the parent's body than from that body itself. The
parental body is the trustee rather than the producer of the germ-cells.
_A Digression._--Here we must digress a little to compare Spencer's
conception of physiological or constitutional units with Weismann's
conception of the Germ-Plasm. According to Weismann, there is in the
nuclei of the germ-cells a distinctive physical basis of inheritance,
the germ-plasm. It is the vehicle of the hereditary qualities, the
architectural substance which enables the germ-cell to build up an
organism; it has an extremely complex and at the same time persistent
structure. Following a hypothesis of De Vries, he supposed that the
readily stainable nuclear bodies (the chromosomes or idants) consist of
a colony of invisible self-propagating vital units or _biophors_, each
of which has the power of expressing in development some particular
quality. He supposed that these biophors are aggregated into units of a
higher order, known as _determinants_, one for each structure of the
body which is capable of independent variation. These determinants are
supposed to be grouped together in _ids_, each of which is supposed to
possess a complete complement of the specific characters of the organism
and also to have an individual character. The _ids_ are arranged in
linear series to form the visible _idants_ or chromosomes, which will be
slightly different from one another according to the individualities of
the component ids. When the fertilised egg-cell develops, it gives rise
(1) to _somatic_ cells which carry with them part of the germ-plasm, and
differentiate to form the body, and (2) to the _germ_ cells which
reserve part of the germ-plasm in an unchanged state, and eventually
give rise in appropriate conditions to new individuals _and their
germ-cells_.
Spencer refused to accept the contrast between _body_-cells and
_germ_-cells as expressing a fact, and referred for his reasons to the
numerous cases in which small pieces of a plant or polyp may grow into
an entire organism. But when he represented Weismann as maintaining that
the "soma contains in its components none of those latent powers
possessed by those of the germ-plasm," he did not do justice to the
comprehensive theory of the "Germ-plasm." For Weismann assumes that in
certain cases the body-cells, even though differentiated, may carry with
them some residual unused-up germ-plasm.
When a lizard regrows a lost tail--effectively responding to a casualty
which has been common for untold generations--Weismann interprets the
mechanism of this as due to a reserve of tail-determinants resident at
or near the place of breakage, and localised there as the result of a
long-continued process of selection. A chamaeleon does not regenerate
its tail, and this may be interpreted in terms of the selection-theory,
since the chamaeleon with its tail coiled up or embracing a branch has
not been, in the course of its evolution, subjected to the frequently
recurrent casualty which has beset most other lizards. Spencer said, "We
cannot arbitrarily assume that wherever a missing organ has to be
reproduced there exists the needful supply of determinants representing
that organ," but Weismann made no such arbitrary assumption. Many organs
are lost which are not regenerated, even when, as far as materials or
differentiation are concerned, it would be easy to replace them. Why the
everywhere present uniform physiological units that Spencer believed in
should not replace them, we do not know; but if the distribution of
regenerative determinants has been wrought out by selection, we
understand the facts.
Spencer said that the hypothesis of a supply of determinants lying
latent at or near the seat of injury, and able to reproduce the missing
part in all its details, and to do this several times over, was "a
strong supposition." We venture to think that the hypothesis that the
same result is achieved by the "physiological units," which are all of
the same kind, is a weak supposition. Spencer said: "Reproduction of the
lost part would seem to be a normal result of the proclivity towards the
form of the entire organism." But it is difficult to see why "proclivity
of the physiological units towards the form of the entire organism"
should bring about the regeneration of a tail here and a head there, a
claw here and an eye there. But Spencer was too acute a thinker not to
feel that if the theory of regenerative determinants was "incompetent,"
his own theory, which interpreted regeneration as due to the activity of
physiological units, "with a proclivity towards the organic form of the
species," did not cover the facts; _e.g._ the establishment of
"false-joints," where the ends of a broken bone failing to unite remain
movable one upon the other. Therefore he suggested a qualification of
his hypothesis.
In "the social organism," it is often seen that the components of an
aggregate "have their activities and arrangements mainly settled by
local conditions." "A local group of units, determined by circumstances
towards a certain structure, coerces its individual units into that
structure." In an emigrant settlement, "individuals are led into
occupations and official posts, often quite new to them, by the wants of
those around--are now influenced and now coerced into social
arrangements which, as shown perhaps by gambling saloons, by shootings
at sight, and by lynchings, are scarcely at all affected by the central
government. Now the physiological units in each species appear to have a
similar combination of capacities. Besides their general proclivity
towards specific organisation, they show us abilities to organise
themselves locally; and these abilities are in some cases displayed in
defiance of the general control, as in the supernumerary finger or the
false joint. Apparently each physiological unit, while having in a
manner the whole organism as the structure which, along with the rest,
it tends to form, has also an aptitude to take part in forming any local
structure, and to assume its place in that structure under the
influence of adjacent physiological units" (_Principles of Biology_,
revised edition, i. p. 364).
The experiments of Born and others have shown that fragments of a young
tadpole may go on developing to some extent after they are cut off, and
that the undifferentiated rudiment of a limb may be successfully grafted
on to another tadpole. "In brief, we may say that each part is in chief
measure autogenous." "Though all parts are composed of physiological
units of the same nature, yet everywhere, in virtue of local conditions
and the influence of its neighbours, each unit joins in forming the
particular structure appropriate to its place." This conclusion is very
interesting when compared with that reached more inductively by many
embryologists (of the so-called epigenetic school), namely, that what a
blastomere or cleavage-cell of an egg does, is determined by its
intra-embryonic environment, by its relations, both statical and
dynamical, to the whole organisation of which it forms a part. As
Driesch puts it: "The relative position of a blastomere in the whole
determines in general what develops from it; if its position be changed,
it gives rise to something different; in other words, its prospective
value is a function of its position." But those who assume heterogeneous
determinants do not thereby exclude what truth there may be in this view
that what an early blastomere does is a function of its inter-relations.
But let us consider how much Spencer puts to the credit of his
"constitutional units." (1) They carry within them the traits of the
species and even some of the traits of the ancestors of the species,
the traits of the parents and even some of the traits of their
immediate ancestors, and the congenital idiosyncrasies of the individual
itself. In this they resemble the germ-plasm. (2) They "must be at once
in some respects fixed and in other respects plastic; while their
fundamental traits, expressing the structure of the type, must be
unchangeable, their superficial traits must admit of modification
without much difficulty; and the modified traits, expressing variations
in the parents and immediate ancestors, though unstable, must be
considered as capable of becoming stable in course of time." Again they
resemble the germ-plasm. (3) Once more, "we have to think of these
physiological units (or constitutional units as I would now re-name
them) as having such natures that while a minute modification,
representing some small change of local structure, is inoperative on the
proclivities of the units throughout the rest of the system, it becomes
operative in the units which fall into the locality where that change
occurs." Here they part company from the germ-plasm, except in so far as
it may be said that the development of the distributed determinants is
in part dependent on local conditions. (4) Finally, since Spencer
supposed "an unceasing circulation of protoplasm throughout an
organism," such that "in the course of days, weeks, months, years, each
portion of protoplasm visits every part of the body"--a wild
assumption--"we must conceive that the complex forces of which each
constitutional unit is the centre, and by which it acts on other units
while it is acted on by them, tend continually to re-mould each unit
into congruity with the structures around: superposing on it
modifications answering to the modifications which have arisen in these
structures. Whence is to be drawn the corollary that in the course of
time all the circulating units--physiological, or constitutional if we
prefer so to call them--visit all parts of the organism; are severally
bearers of traits expressing local modifications; and that those units
which are eventually gathered into sperm-cells and germ-cells also bear
these superposed traits."
This theory--which is not unlike a combination of Darwin's pangenesis
with De Vries's neo-pangenesis--is very significant, for it discloses
Spencer's hypothesis as to the _modus operandi_ of the transmission of
acquired characters. But there is unfortunately no factual warrant for
the assumption that the constitutional units visit one another in
various corners of the body, getting impressions as they go, or for the
assumption that they are eventually gathered into the germ-cells--an
assumption which shows how far Spencer deliberately stood from the
conception of the continuity of the germ-plasm. Even if we suppose an
organism to undergo numerous modifications in different parts of its
body, as a plant may do when it is transferred from the Alps to the
lowlands; even if we suppose the constitutional units--which are all of
one kind--to circulate and become bearers of the traits expressing local
modifications, we have to face other questions: do they all become
remoulded in relation to all the modifications? or do some become
remoulded in relation to one modification and some in relation to
another? or do all the modifications so hang together that one kind of
alteration impressed upon the constitutional units covers them all? The
difficulties of the conception of constitutional-units certainly do not
seem less than the difficulties of the conception of specific
determinants.
Even to the general reader, who is not concerned with the problem of the
mechanism of inheritance and development, who has a shrewd suspicion
that it is one of those things no fellow can understand, our digression
should be interesting, for it illustrates Spencer's fertility of
invention and his adroitness in lugging in one hypothesis after another
to eke out a theory which in its first statement appears to be very
simple. It is instructive to observe how the constitutional units at
first so harmlessly simple, grow under the conjurer's hands until they
become more marvellous than Clerk Maxwell's "sorting demons."
But it is more instructive still to hear the conclusion of the whole
matter. "At last then we are obliged to admit that the actual organising
process transcends conception. It is not enough to say that we cannot
know it; we must say that we cannot even conceive it. And this is just
the conclusion which might have been drawn before contemplating the
facts. For if, as we saw in the chapter on "the Dynamic Element in
Life," it is impossible for us to understand the nature of this
element--if even the ordinary manifestations of it which a living body
yields from moment to moment are at bottom incomprehensible; then still
more incomprehensible must be that astonishing manifestation of it which
we have in the initiation and unfolding of a new organism." "Thus all we
can do is to find some way of symbolising the process so as to enable us
most conveniently to generalise its phenomena; and the only reason for
adopting the hypothesis is that it best serves this purpose."
But the hypothesis only serves the purpose because the constitutional
units are gradually invested with the powers of effective response,
co-ordination, and the like which remain the secret of the organism as a
whole--the secret of life, which many think will never be read until we
recognise that it is also the secret of mind.
_The Germ-Cells._--According to Spencer, "sperm-cells and germ-cells are
essentially nothing more than vehicles in which are contained small
groups of the physiological units in a fit state for obeying their
proclivity towards the structural arrangement of the species they belong
to," and "if the likeness of offspring to parents is thus determined, it
becomes manifest, _a priori_, that besides the transmission of generic
and specific peculiarities, there will be a transmission of those
individual peculiarities which, arising without assignable causes, are
classed as spontaneous." Not only are the main characters transmitted,
the same may be true of even minute details--varietal characters, like
the taillessness of Manx cats, and individual congenital peculiarities
such as a sixth finger; normal qualities such as swiftness in
race-horses, abnormal qualities such as nervousness in man. Here Spencer
was of course at one with all biologists.
_Transmission of Acquired Characters._--He went on, however, to try to
substantiate the proposition, which has been the subject of so much
discussion, that modifications or acquired bodily characters are also
transmissible, and we must follow his argument carefully.
He first points out that when a structure is altered by a change of
function the modification is often unobtrusive, and its transmission
consequently difficult to detect. "Moreover, such specialities of
structure as are due to specialities of function, are usually entangled
with specialities which are, or may be, due to selection, natural or
artificial. In most cases it is impossible to say that a structural
peculiarity which seems to have arisen in offspring from a functional
peculiarity in a parent, is wholly independent of some congenital
peculiarity of structure in the parent, whence this functional
peculiarity arose. We are restricted to cases with which natural or
artificial selection can have had nothing to do, and such cases are
difficult to find. Some, however, may be noted."
When a plant is transferred from one soil to another it undergoes "a
change of habit"; its leaves may become hairy, its stem woody, its
branches drooping. "These are modifications of structure consequent on
modifications of function that have been produced by modifications in
the actions of external forces. And as these modifications
reappear in succeeding generations, we have, in them, examples of
functionally-established variations that are hereditarily transmitted."
But this is a _non sequitur_, since the modifications may reappear
merely _because they are re-impressed directly_ on each successive
generation.
Spencer notes that in the domestic duck the bones of the wing weigh less
and the bones of the leg more in proportion to the whole skeleton than
do the same bones in the wild duck; that in cows and goats which are
habitually milked the udders are large; that moles and many
cave-animals have rudimentary eyes, and so on. But all these results may
be readily interpreted as due to selection of germinal variations.
The best examples of inherited modifications occur, he says, in mankind.
"Thus in the United States the descendants of the immigrant Irish lose
their Celtic aspect, and become Americanised.... To say that
'spontaneous variation' increased by natural selection can have produced
this effect is going too far." But if the vague statement as to the
Americanisation of the Irishman be correct, and if it be true that
intermarriage is rare, it remains probable that the Americanisation is a
modificational veneer impressed afresh on each successive generation.
"That large hands are inherited by those whose ancestors led laborious
lives, and that those descended from ancestors unused to manual labour
commonly have small hands, are established opinions." But if we accept
the fact, it is easy to interpret the size of the hands as a
stock-character correlated with a muscularity and vigour, and
established by selection. The prevalence of short-sightedness among the
"notoriously studious" Germans is a singularly unfortunate instance to
give in support of the inheritance of functional modifications, for
there is no reason to believe that short-sightedness is primarily an
acquired character. Nor is it confined to readers.
Spencer twits those who are sceptical as to the transmission of acquired
modifications, for assigning the most flimsy reasons for rejecting a
conclusion they are averse to; but when Spencer cites the inheritance of
musical talent and a liability to consumption as evidence of the
transmission of functional modifications, we are reminded of the pot
calling the kettle black.
Spencer made his position stronger by adducing what he calls _negative_
evidence, namely those "cases in which traits otherwise inexplicable are
explained if the structural effects of use and disuse are transmitted."
(1) First he refers to the co-adaptation of co-operative parts.
With the enormous antlers of a stag there is associated a large
number of co-adaptations of different parts of the body, and
similarly with the giraffe's long neck and the kangaroo's power of
leaping. Spencer argued that the co-adaptation of numerous parts
cannot have been effected by natural selection, but might be
effected by the hereditary accumulation of the results of use. The
difficulty is to discover how much deep-seated co-adjustment can be
effected by exercise even in the course of a long time, and the
theory requires such data before it can be more than a plausible
interpretation, with certain _a priori_ difficulties against it. If
an animal suddenly takes to leaping many individual adjustments to
the new exercise will arise; if the animals of successive
generations leap yet more freely, they will individually acquire
more thorough adjustments up to a certain limit; meanwhile there
may arise constitutional variations making towards adaptation to
the new habit, and under the screen of the individual modifications
these may increase from minute beginnings till they acquire
selection-value. Professors Mark Baldwin, Lloyd Morgan, and Osborn,
have all made the same useful suggestion that adaptive
modifications acquired individually may act as the fostering nurses
of constitutional variations in the same direction until these
coincident variations are large enough in amount to be themselves
effective.
(2) Secondly, Spencer dwelt upon the notably unlike powers of
tactile discrimination possessed by the human skin, and sought to
show that while these could not be interpreted on the hypothesis of
natural selection or on the correlated hypothesis of panmixia, they
could be interpreted readily if the effects of use are inherited.
But the difficulty again is to get secure data. It is uncertain
how much of the inequality in tactile sensitiveness is due to
individual exercise and experience, though it is certain that
tactility in little-used parts can be greatly increased by use. Nor
is it certain how much of the apparent unlikeness in tactility is
due to unequal distribution of peripheral nerve-endings and how
much to specialised application of the power of central perception.
As Prof. Lloyd Morgan says: "We do not yet know the limits within
which education and practice may refine the application of central
powers of discrimination within little-used areas. The facts which
Mr Spencer adduces may be in large degree due to individual
experience; discrimination being continually exercised in the
tongue and finger-tips, but seldom on the back or breast. We need a
broader basis of assured fact." Nor, it may be added, is the action
of selection to be excluded.
(3) Spencer's third set of negative evidences was based on
rudimentary organs which, like the hind limbs of the whale, have
nearly disappeared. Dwindling by natural selection is here out of
the question; and dwindling by panmixia, i.e. the diminution of a
structure when natural selection ceases to affect its degree of
development, "would be incredible, even were the assumptions of the
theory valid." But as a sequence of disuse the change is clearly
explained. Prof. Lloyd Morgan replies: "Is there any evidence that
a structure really dwindles through disuse in the course of
individual life? Let us be sure of this before we accept the
argument that vestigial organs afford evidence that this supposed
dwindling is inherited. The assertion may be hazarded that, in the
individual life, what the evidence shows is that, without due use,
an organ does not reach its full functional or structural
development. If this be so, the question follows: How is the mere
absence of full development in the individual converted through
heredity into a positive dwindling of the organ in question?"
Moreover, the convinced Neo-Darwinian is not in the least prepared
to abandon the theory of dwindling in the course of panmixia,
especially in the light which Weismann's conception of Germinal
Selection has thrown on this process.
The inductive evidence in support of the conclusion that bodily
modifications due to use or disuse or environmental influence can be as
such or in any representative degree transmitted, is very weak. The
so-called evidences are often anecdotal and vague, often irrelevant and
fallacious, and those Spencer adduced are by no means convincing. Let us
consider the question briefly from the _a priori_ side.
The general argument _against_ the hypothesis rests on a realisation of
the continuity of the germ-plasm. For if the germ-plasm, or the material
basis of inheritance within the germ-cells, be somewhat apart from the
general life of the body, often segregated at an early stage, and in any
case not directly sharing in the every day metabolism, then there is a
presumption against the likelihood of its being readily affected in a
specific manner by changes in the nature of the body-cells. The
germ-cell is in a sense so apart that it is difficult to conceive of the
mechanism by which it might be influenced in a specific or
representative manner by changes in the cells of the body.
On the other hand, in many plants and lower animals, the distinction
between body-cells and germ-cells is far from being demonstrably marked,
and even in higher animals we cannot think of the germ-cells as if they
led a charmed life uninfluenced by any of the accidents and incidents in
the daily life of the body which is their nurse, though not exactly
their parent. No one believes this, Weismann least of all, for he finds
one of the chief sources of germinal variation in the nutritive stimuli
exerted on the germ-plasm by the varying state of the body. The organism
is a unity; the blood and lymph and other body-fluids form a common
internal medium; various poisons may affect the whole system,
germ-cells included; and there are real though dimly understood
correlations between the reproductive system and the rest of the
organism.
There are some who pretend to find in this admission "a concealed
abandonment of the central position of Weismann," for if, they say, the
germ-plasm is affected by changes in nutrition in the body, and if
acquired characters affect changes in nutrition, then "acquired
characters or their consequences will be inherited." But it is a quite
illegitimate confusion of the issue to slump acquired characters and
their consequences as if the distinction was immaterial. The illustrious
author of the _Germ-Plasm_ has made it quite clear that there is a great
difference between admitting that the germ-plasm has no charmed life,
insulated from bodily influences, and admitting the transmissibility _of
a particular acquired character_, even in the faintest degree. The whole
point is this: Does a change in the body, induced by use or disuse or by
a change in surroundings, influence the germ-plasm in such a specific or
representative way that the offspring will exhibit the same modification
which the parent acquired, or even a tendency towards it? Even when we
fully recognise the unity of the organism, or recognise it as fully as
we know how, it is difficult to suggest any _modus operandi_ whereby a
particular modification in, say, the brain or the thumb can specifically
affect the germinal material in such a way that the modification or a
tendency towards it becomes part of the inheritance. Did we accept
Darwin's provisional hypothesis of pangenesis according to which the
parts of the body give off gemmules which are carried as samples to the
germ-cells, the possibility of transfer might seem more intelligible.
But Darwin's suggestion remains a pure hypothesis, and is admitted by
none except in extremely modified form. In fairness, however, we must
note how little we understand of the _modus operandi_ of influences
which certainly pass in the other direction, from the reproductive
organs to the body; we must recall Prof. Lloyd Morgan's warning that
although we cannot conceive how a modification might as such saturate
from body to germ-cells, this does not exclude the possibility that it
may actually do so.
As a matter of fact, Spencer has himself suggested a _modus
operandi_--as already outlined. The constitutional units are supposed to
circulate; when they come to a modified organ and visit its modified
constitutional units, they are supposed to be themselves impressed; they
are supposed to be "eventually gathered into sperm-cells and
germ-cells," which thus come to bear the "superposed traits" resulting
from modification. But, as we have seen, the difficulty is to find any
basis in fact on which these assumptions can rest. Indeed, they are
contradictory to well-established physiological facts.
_Inconceivability._--In reference to the difficulties which beset
theories of heredity, Spencer remarks:--
"If it is said that the mode in which functionally-wrought changes,
especially in small parts, so affect the reproductive elements as
to repeat themselves in offspring, cannot be imagined--if it be
held inconceivable that those minute changes in the organ of vision
which cause myopia can be transmitted through the appropriately
modified sperm-cells or germ-cells; then the reply is that the
opposed hypothesis presents a corresponding inconceivability.
Grant that the habit of a pointer was produced by selection of
those in which an appropriate variation in the nervous system had
occurred; it is impossible to imagine how a slightly different
arrangement of a few nerve-cells and fibres could be conveyed by a
spermatozoon. So too it is impossible to imagine how in a
spermatozoon there can be conveyed the 480,000 independent
variables required for the construction of a single peacock's
feather, each having a proclivity towards its proper place. Clearly
the ultimate process by which inheritance is effected in either
case passes comprehension; and in this respect neither hypothesis
has an advantage over the other."
Let us consider what Spencer has said in regard to
"inconceivability." Most ova are very minute cells, often
microscopically minute, and a spermatozoon may be only 1/100,000th
of the ovum's size--inconceivably minute, but yet exceedingly real
and potent. We cannot conceive how a complex inheritance made up of
numerous contributions is potentially contained in such small
compass, and yet in some form it must be. Similarly, we cannot
conceive how the pin-head like brain of the ant contains all the
ant's "wisdom."
Those who find it difficult to believe that items so minute as the
germ-cells can have room for the complexity of hereditary
organisation which seems to be a necessary postulate may be
reminded of three things: (1) They should recall what students of
physics have told us in regard to the fineness, or, from another
point of view, the coarse-grainedness of matter. They tell us that
the picture of a Great Eastern filled with framework as intricate
as that of the daintiest watches does not exaggerate the
possibilities of molecular complexity in a spermatozoon, whose
actual size is usually very much less than the smallest dot on the
watch's face.
(2) It should be remembered that in development one step conditions
the next, and one structure grows out of another, so that there is
no need to think of the microscopic germ-cells as stocked with more
than _initiatives_. (3) It should be remembered that every
development implies an interaction between the growing organism and
a complex environment without which the inheritance would remain
unexpressed, and that the full-grown organism includes much that
was not as such inherited, but has been individually acquired as
the result of nurture or external influence.
Now, returning to Spencer, we find that by an extraordinary
argument he concludes that the number of determinants required for
the development of a single feather in the peacock's tail must be
480,000, and he points to the inconceivability of these being
contained, along with much else of course, in the spermatozoon. We
are not at present concerned with the precise number of
determinants, but we can see no reason why a spermatozoon should
not contain millions if they were needed. The inconceivability is a
general one; it is due to the difficulty of imaging the complexity
of matter.
But the inconceivability of a particular modification of the nose
affecting the germ-cells in a specific and representative way is a
different kind of inconceivability. It is due to our being unable
to imagine any reasonable _modus operandi_ consistent with our
knowledge of the structure and metabolism of the organism. As we
have seen and emphasised Spencer does himself suggest a _modus
operandi_, but it seems to us to make unwarranted assumptions, and
is for that reason to us "inconceivable."
_A Priori Argument._--But Spencer advanced an _a priori_ argument to
strengthen the position which he felt bound to hold--the
transmissibility of acquired characters. "That changes of structure
caused by changes of action must be transmitted, however obscurely,
appears to be a deduction from first principles--or if not a specific
deduction, still, a general implication. For if an organism A, has, by
any peculiar habit or condition of life, been modified into the form A',
it follows that all the functions of A', reproductive function included,
must be in some degree different from the functions of A." [This, we
venture to think, must depend on the nature and amount of the
modification.] "An organism being a combination of rhythmically-acting
parts in moving equilibrium, the action and structure of any one part
cannot be altered without causing alterations of action and structure in
all the rest." [The appreciability of the change will depend on the
amount and nature of the modification, and on the intimacy of the
correlation subsisting in the organism. Dislodging a rock may alter the
centre of gravity of the earth, but it does not do so appreciably.] "And
if the organism A, when changed to A', must be changed in all its
functions; then the offspring of A' cannot be the same as they would
have been had it retained the form A." [Assuming that is to say that the
change in the physiological units of the body affects the physiological
units in the germ-cells.] "That the change in the offspring must, other
things equal, be in the same direction as the change in the parent,
appears implied by the fact that the change propagated throughout the
parental system is a change towards a new state of equilibrium--a change
tending to bring the actions of all organs, reproductive included, into
harmony with these new actions." [It seems to us to pass the wit of man
to conceive how or why an improved equilibrium in the use of the hand
should involve any corresponding or representative change of equilibrium
in the germ-cells.]
Spencer seems to have seen the matter quite clearly. If the
physiological units in the germ-cell mould the aggregate organism, the
organism modified by incident actions will impress some corresponding
modifications on the structures and polarities of its units. And if the
physiological units are in any degree so remoulded as to bring their
polar forces towards equilibrium with the forces of the modified
aggregate, then, when separated in the shape of reproductive centres,
these units will tend to build themselves up into an aggregate modified
in the same direction.
The drawback to abstract biology based on first principles is that it
enables its devotee to develop arguments which seem plausible until they
are reduced to the concrete. Why had Herbert Spencer small hands?
Because his grandfather and father were schoolmasters who did little
from day to day but wield the pen and sharpen the pencil! Through disuse
of the sword and the spade their hands were directly equilibrated
towards smallness. But since Mr Spencer senior, was "a combination of
rhythmically-acting parts in moving equilibrium," the dwindling of the
hands and the moulding of the physiological units thereof reverberated
through the whole aggregate; a change towards a new state of equilibrium
"was propagated throughout the parental system--a change tending to
bring the actions of all organs, reproductive included, into harmony
with these new actions," or inactions. The modified aggregate impressed
some corresponding modification on the structures and polarities of the
germ-units. And this was why Herbert Spencer had small hands. At least
so he tells us, for the instance is his own.
_Practical Conclusion._--It is obvious that we have not in these pages
attempted to give an adequate discussion of an extremely difficult
problem. We have endeavoured to give a fair statement of Spencer's
position in regard to a question which appeared to him of "transcendent
importance." "A right answer to the question whether acquired
characters are or are not inherited, underlies right beliefs, not only
in Biology and Psychology, but also in Education, Ethics, and Politics."
"A grave responsibility rests on biologists in respect of the general
question; since wrong answers lead, among other effects, to wrong
beliefs about social affairs and to disastrous social actions."
It cannot be an easy question this, when we find Spencer on one side and
Weismann on the other, Haeckel on one side and Ray Lankester on the
other, Turner on one side and His on the other. Therefore while it seems
to us that the transmission of acquired characters as strictly defined
is non-proven, and while there seems to us to be a strong presumption
that they are not transmitted, the scientific position should remain one
of active scepticism--leading on to experiment.
And if there is little scientific warrant for our being other than
sceptical at present as to the transmission of acquired characters, this
scepticism lends greater importance than ever, on the one hand, to a
good "nature," to secure which is the business of careful mating; and,
on the other hand, to a good "nurture," to secure which for our children
is one of our most obvious duties, the hopefulness of the task resting
upon the fact that, unlike the beasts that perish, man has a lasting
external heritage, capable of endless modification for the better, a
heritage of ideas and ideals embodied in prose and verse, in statue and
painting, in Cathedral and University, in tradition and convention, and
above all in society itself.