difficult question of definition in oral debate. Therefore I allude to
this fiasco at the British Association, merely for the purpose of
emphasizing the necessity of agreeing upon some definition of a species,
before we can conclude anything with regard to the generalization of
specific characters as necessarily due to natural selection. But when a
naturalist has had full time to consider this fundamental matter of
definition, and to decide on what his own shall be, he cannot complain
of unfairness on the part of any one else who holds him to what he thus
says he means by a species. Now Mr. Wallace, in his last work, has given
a matured statement of what it is that he means by a species. This,
therefore, I will take as the avowed basis of his doctrine touching the
necessary origin and maintenance of all specific characters by natural
selection. His definition is as follows:--
"An assemblage of individuals which have become somewhat modified
in structure, form, and constitution, _so as to adapt them to
slightly different conditions of life_; which can be differentiated
from allied assemblages; which reproduce their like; which usually
breed together; and, perhaps, when crossed with their near allies,
always produce offspring which are more or less sterile _inter
se_[123]."
[123] Darwinism, p. 167.
From this definition the portion which I have italicized must be omitted
in the present discussion, for the reasons already given while
considering definition No. 5. What remains is a combination of Nos. 2
and 4. According to Mr. Wallace, therefore, our criterion of a species
is to be the heredity of peculiar characters, combined, perhaps, with a
more or less exclusive fertility of the component individuals _inter
se_. This is the basis on which his generalization of the utility of
specific characters as necessary and universal is reared. Here, then, we
have something definite to go upon, at all events as far as Mr. Wallace
is concerned. Let us see how far such a basis of definition is competent
to sustain his generalization.
First of all it must be remarked that, as species have actually been
constituted by systematists, the test of exclusive fertility does not
apply. For my own part I think this is to be regretted, because I
believe that such is the only natural--and therefore the only
firm--basis on which specific distinctions can be reared. But, as
previously observed, this is not the view which has been taken by our
species-makers. At most they regard the physiological criterion as but
lending some additional weight to their judgement upon morphological
features, in cases where it is doubtful whether the latter alone are of
sufficient distinctness to justify a recognition of specific value. Or,
conversely, if the morphological features are clearly sufficient to
justify such a recognition, yet if it happens to be known that there is
full fertility between the form presenting them and other forms which do
not, then the latter fact will usually prevent naturalists from
constituting the well differentiated form a species on grounds of its
morphological features alone--as, for instance, in the case of our
domesticated varieties. In short, the physiological criterion has not
been employed with sufficient closeness to admit of its being now
comprised within any practical definition of the term "species"--if by
this term we are to understand, not what any one may think species
_ought to be_, but what species actually _are_, as they have been
constituted for us by their makers.
From all this it follows that the definition of the term "species" on
which Mr. Wallace relies for his deduction with respect to specific
characters, is the definition No. 4. In other words, omitting his
_petitio principii_ and his allusion to the test of fertility, the great
criterion in his view is the criterion of Heredity. And in this all
other evolutionists, of whatever school, will doubtless agree with him.
They will recognize that it is really the distinguishing test between
"climatic varieties" and "true species," so that however widely or
however constantly the former may diverge from one another in regard to
their peculiar characters, they are not to be classed among the latter
unless their peculiar characters are likewise hereditary characters.
Now, if we are all agreed so far, the only question that remains is
whether or not this criterion of Heredity is capable of supplying a
basis for the generalization, that all characters which have been ranked
as of specific value must necessarily be regarded as presenting also an
adaptive, or life-serving, value? I will now endeavour to show that
there are certain very good reasons for answering this question in the
negative.
(A.)
In the first place, even if the modifications induced by the direct
action of a changed environment are not hereditary, who is to know that
they are not? Assuredly not the botanist or zoologist who in a
particular area finds what he is fully entitled to regard as a
well-marked specific type. Only by experiments in transposition could it
be proved that the modifications have been produced by local conditions;
and although the researches of many experimentalists have shown how
considerable and how constant such modifications may be, where is the
systematic botanist who would ever think of transplanting an apparently
new species from one distant area to another before he concludes that it
is a new species? Or where is the systematic zoologist who would take
the trouble to transport what appears to be an obviously endemic species
of animal from one country to another before venturing to give it a new
specific name? No doubt, both in the case of plants and animals, it is
tacitly assumed that constant differences, if sufficient in amount to be
regarded as specific differences are hereditary; but there is not one
case in a hundred where the validity of this assumption has ever been
tested by experiments in transposition. Therefore naturalists are apt to
regard it as remarkable when the few experiments which have been made in
this direction are found to negative their assumption--for example,
that a diagnostic character in species of the genus _Hieratium_ is found
by transplantation not to be hereditary, or that the several named
species of British trout are similarly proved to be all "local
varieties" of one another. But, in point of fact, there ought to be
nothing to surprise us in such results--unless, indeed, it is the
unwarrantable nature of the assumption that any given differences of
size, form, colour, &c., which naturalists may have regarded as of
specific value, are, on this account, hereditary. Indeed, so surprising
is this assumption in the face of what we know touching both the extent
and the constancy of climatic variation, that it seems to me such a
naturalist as Kerner, who never considers the criterion of heredity at
all, is less assailable than those who profess to constitute this their
chief criterion of specific distinction. For it is certain that whatever
their professions may have nowadays become, systematic naturalists have
never been in the habit of really following this criterion. In theory
they have of late years attached more and more weight to definition No.
4; but in practice they have always adopted definition No. 3. The
consequence is, that in literally numberless cases (particularly in the
vegetable kingdom) "specific characters" are assumed to be hereditary
characters merely because systematic naturalists have bestowed a
specific name on the form which presents them. Nor is this all. For,
conversely, even when it is known that constant morphological characters
are unquestionably hereditary characters, if they happen to present but
small degrees of divergence from those of allied forms, then the form
which presents them is not ranked as a species, but as a constant
variety. In other words, when definitions 3 and 4 are found to clash, it
is not 4, but 3, that is followed. In short, even up to the present
time, systematic naturalists play fast and loose with the criterion of
Heredity to such an extent, that, as above observed, it has been
rendered wellnigh worthless in fact, whatever may be thought of it in
theory.
Now, unless all this can be denied, what is the use of representing that
a species is distinguished from a variety--"climatic" or otherwise--by
the fact that its constituent individuals "reproduce their like"? We are
not here engaged on any abstract question of what might have been the
best principles of specific distinction for naturalists to have adopted.
We are engaged on the practical question of the principles which they
actually have adopted. And of these principles the reproduction of like
by like, under all circumstances of environment, has been virtually
ignored.
(B.)
In the second place, supposing that the criterion of Heredity had been
as universally and as rigidly employed by our systematists in their work
of constructing species as it has been but occasionally and loosely
employed, could it be said that even then a basis would have been
furnished for the doctrine that all specific characters must necessarily
be useful characters? Obviously not, and for the following reasons.
It is admitted that climatic characters are not necessarily--or even
generally--useful characters. Consequently, if there be any reason for
believing that climatic characters may become in time hereditary
characters, the doctrine in question would collapse, even supposing that
all specific types were to be re-constituted on a basis of experimental
inquiry, for the purpose of ascertaining which of them conform to the
test of Heredity. Now there are very good reasons for believing that
climatic characters not unfrequently do become hereditary characters;
and it was mainly in view of those reasons that I deemed it worth while
to devote so much space in the preceding chapter to the facts of
climatic variation. I will now state the reasons in question under two
different lines of argument.
We are not as yet entitled to conclude definitely against the possible
inheritance of acquired characters. Consequently, we are not as yet
entitled to assume that climatic characters--i. e. characters acquired
by converse with a new environment, continued, say, since the last
glacial period--can never have become congenital characters. But, if
they ever have become congenital characters, they will have become, at
all events as a general rule, congenital characters that are useless;
for it is conceded that, _qua_ climatic characters, they have not been
due to natural selection.
Doubtless the followers of Weismann will repudiate this line of
argument, if not as entirely worthless, at all events as too
questionable to be of much practical worth. But even to the followers of
Weismann it may be pointed out, that the Wallacean doctrine of the
origin of all specific characters by means of natural selection was
propounded many years before either Galton or Weismann had questioned
the transmission of acquired characters. However. I allow that this line
of argument has now become--for the time being at all events--a dubious
line, and will therefore at once pass on to the second line, which is
not open to doubt from any quarter.
Whether or not we accept Weismann's views, it will here be convenient to
employ his terminology, since this will serve to convey the somewhat
important distinctions which it is now my object to express.
In the foregoing paragraphs, under heading (A), we have seen that there
must be "literally numberless forms" which have been ranked as true
species, whose diagnostic characters are nevertheless not congenital. In
the case of plants especially, we know that there must be large numbers
of named species which do not conform to the criterion of Heredity,
although we do not know which species they are. For present purposes,
however, it is enough for us to know that there are many such named
species, where some change of environment has acted directly and
similarly on all the individual "somas" exposed to it, without affecting
their "germ-plasms," or the material bases of their hereditary
qualities. For named species of this kind we may employ the term
_somatogenetic species_.
But now, if there are any cases where a change of environment does act
on the germ-plasms exposed to it, the result would be what we may call
_blastogenetic species_--i.e. species which conform to the criterion of
Heredity, and would therefore be ranked by all naturalists as "true
species." It would not signify in such a case whether the changed
conditions of life first affected the soma, and then, through changed
nutrition, the germ-plasm; or whether from the first it directly
affected the germ-plasm itself. For in either case the result would be a
"species," which would continue to reproduce its peculiar features by
heredity.
Now, the supposition that changed conditions of life may thus affect the
congenital endowments of germ-plasm is not a gratuitous one. The sundry
facts already given in previous chapters are enough to show that the
origin of a blastogenetic species by the direct action on germ-plasm of
changed conditions of life is, at all events, a possibility. And a
little further thought is enough to show that this possibility becomes a
probability--if not a virtual certainty. Even Weismann--notwithstanding
his desire to maintain, as far as he possibly can, the "stability" of
germ-plasm--is obliged to allow that external conditions acting on the
organism may in some cases modify the hereditary qualities of its
germ-plasm, and so, as he says, "determine the phyletic development of
its descendants." Again, we have seen that he is compelled to interpret
the results of his own experiments on the climatic varieties of certain
butterflies by saying, "I cannot explain the facts otherwise than by
supposing the passive acquisition of characters produced by direct
influences of climate"; by which he means that in this case the
influence of climate acts directly on the hereditary qualities of
germ-plasm. Lastly, and more generally, he says:--
"But although I hold it improbable that individual variability can
depend on a direct action of external influences upon the
germ-cells and their contained germ-plasm, because--as follows from
sundry facts--the molecular structure of the germ-plasm must be
very difficult to change, yet it is by no means to be implied that
this structure may not possibly be altered by influences of the
same kind continuing for a very long time. Thus it seems to me the
possibility is not to be rejected, that influences continued for a
long time, that is, for generations, such as temperature, kind of
nourishment, &c., which may affect the germ-cells as well as any
other part of the organism, may produce a change in the
constitution of the germ-plasm. But such influences would not then
produce individual variation, but would necessarily modify in the
same way all the individuals of a species living in a certain
district. It is possible, though it cannot be proved, that many
climatic varieties have arisen in this manner."
So far, then, we have testimony to this point, as it were, from a
reluctant witness. But if we have no theory involving the "stability of
germ-plasm" to maintain, we can scarcely fail to see how susceptible the
germ-plasm is likely to prove to changed conditions of life. For we know
how eminently susceptible it is in this respect when gauged by the
practical test of fertility; and as this is but an expression of its
extraordinarily complex character, it would indeed be surprising if it
were to enjoy any immunity against modification by changed conditions of
life. We have seen in the foregoing chapter how frequently and how
considerably somatogenetic changes are thus caused, so as to produce
"somatogenetic species"--or, where we happen to know that the changes
are not hereditary, "climatic varieties." But the constitution of
germ-plasm is much more complex than that of any of the structures which
are developed therefrom. Consequently, the only wonder is that hitherto
experimentalists have not been more successful in producing
"blastogenetic species" by artificial changes of environment. Or, as Ray
Lankester has well stated this consideration, "It is not difficult to
suggest possible ways in which the changed conditions, shown to be
important by Darwin, could act through the parental body upon the
nuclear matter of the egg-cell and sperm-cell, with its immensely
complex and therefore unstable constitution.... The wonder is, not that
[blastogenetic] variation occurs, but that it is not excessive and
monstrous in every product of fertilization[124]."
[124] _Nature_, Dec. 12, 1889, p. 129.
If to this it should be objected that, as a matter of fact,
experimentalists have not been nearly so successful in producing
congenital modifications of type by changed conditions of life as they
have been in thus producing merely somatic modifications; or if it
should be further objected that we have no evidence at all in nature of
a "blastogenetic species" having been formed by means of climatic
influences alone,--if these objections were to be raised, they would
admit of the following answer.
With regard to experiments, so few have thus far been made upon the
subject, that objections founded on their negative results do not carry
much weight--especially when we remember that these results have not
been uniformly negative, but sometimes positive, as shown in Chapter VI.
With regard to plants and animals in a state of nature, the objection is
wholly futile, for the simple reason that in as many cases as changed
conditions of life may have caused an hereditary change of specific
type, there is now no means of obtaining "evidence" upon the subject.
But we are not on this account entitled to conclude against the
probability of such changes of specific type having been more or less
frequently thus produced. And still less can we be on this account
entitled to conclude against the _possibility_ of such a change having
ever occurred in any single instance. Yet this is what must be concluded
by any one who maintains that the origin of all species--and, _a
fortiori_, of all specific characters--must _necessarily_ have been due
to natural selection.
Now, if all this be admitted--and I do not see how it can be reasonably
questioned--consider how important its bearing becomes on the issue
before us. If germ-plasm (using this term for whatever it is that
constitutes the material basis of heredity) is ever capable of having
its congenital endowments altered by the direct action of external
conditions, the resulting change of hereditary characters, whatever else
it may be, need not be an adaptive change. Indeed, according to
Weismann's theory of germ-plasm, the chances must be infinitely against
the change being an adaptive one. On the theory of pangenesis--that is
to say, on the so-called Lamarckian principles--there would be much more
reason for entertaining the possibly adaptive character of hereditary
change due to the direct action of the environment. Therefore we arrive
at this curious result. The more that we are disposed to accept
Weismann's theory of heredity, and with it the corollary that natural
selection is the sole cause of adaptive modification in species the less
are we entitled to assume that all specific characters must necessarily
be adaptive. Seeing that in nature there are presumably many cases like
those of Hoffmann's plants, Weismann's butterflies, &c., where the
hereditary qualities of germ-plasm have (on his hypothesis) been
modified by changed conditions of life, we are bound to believe that, in
all cases where such changes do not happen to be actively deleterious,
they will persist. And inasmuch as characters which are only of
"specific" value must be the characters most easily--and therefore most
frequently--induced by any slight changes in the constitution of
germ-plasm, while, for the same reason (namely, that of their trivial
nature) they are least likely to prove injurious, it follows that the
less we believe in the functionally-produced adaptations of Lamarck, the
more ought we to resist the assumption that all specific characters must
necessarily be adaptive characters.
* * * * *
Upon the whole, then, and with regard to the direct action of external
conditions, I conclude--not only from general considerations, but also
from special facts or instances quite sufficient for the purpose--that
these must certainly give rise to immense numbers of somatogenetic
species on the one hand, and probably to considerable numbers of
blastogenetic species on the other; that in neither case is there any
reason for supposing the distinctively "specific characters" to be other
than "neutral" or "indifferent"; while there are the best of reasons for
concluding the contrary. So that, under this division of our subject
alone (B), there appears to be ample justification for the statement
that "a large proportional number of specific characters" are in
reality, as they are in appearance, destitute of significance from a
utilitarian point of view.
(C.)
Thus far in the present chapter we have been dealing exclusively with
the case of "climatic variation," or change of specific type due to
changes in the external conditions of life. But it will be remembered
that, in the preceding chapter, allusion was likewise made to changes of
specific type due to internal causes, or to what Darwin has called "the
nature of the organism." Under this division of our subject I mentioned
especially Sexual Selection, which is supposed to arise in the aesthetic
taste of animals themselves; Isolation, which is supposed to originate
new types by allowing the average characters of an isolated section of
an old type to develop a new history of varietal change, as we shall see
more fully in the ensuing part of this treatise; and the Laws of Growth,
which is a general term for the operation of unknown causes of change
incidental to the living processes of organisms which present the
change.
Now, under none of these divisions of our subject can there be any
question touching the criterion of Heredity. For if new species--or even
single specific characters of new species--are ever produced by any of
these causes, they must certainly all "reproduce their like." Therefore
the only question which can here obtain is as to whether or not such
causes ever do originate new species, or even so much as new specific
characters. Mr. Wallace, though not always consistently, answers this
question in the negative; but the great majority of naturalists follow
Darwin by answering it in the affirmative. And this is enough to show
the only point which we need at present concern ourselves with
showing--viz. that the question is, at the least, an open one. For as
long as this question is an open one among believers in the theory of
natural selection, it must clearly be an unwarrantable deduction from
that theory, that all species, and _a fortiori_ all specific characters,
are necessarily due to natural selection. The deduction cannot be
legitimately drawn until the possibility of any other cause of specific
modification has been excluded. But the bare fact of the question as
just stated being still and at the least an open question, is enough to
prove that this possibility has not been excluded. Therefore the
deduction must be, again on this ground alone (C), unwarrantable.
* * * * *
Such are my several reasons--and it is to be observed that they are all
_independent_ reasons--for concluding that it makes no practical
difference to the present discussion whether or not we entertain
Heredity as a criterion of specific distinction. Seeing that our
species-makers have paid so little regard to this criterion, it is
neither absurd nor preposterous to have adduced, in the preceding
chapter, the facts of climatic variation. On the contrary, as the
definition of "species" which has been practically followed by our
species-makers in No. 3, and not No. 4, these facts form part and parcel
of our subject. It is perfectly certain that, in the vegetable kingdom
at all events, "a large proportional number" of specifically diagnostic
characters would be proved by experiment to be "somatogenetic"; while
there are numerous constant characters classed as varietal, although it
is well known that they are "blastogenetic." Moreover, we can scarcely
doubt that many specific characters which are also hereditary characters
owe their existence, not to natural selection, but to the direct action
of external causes on the hereditary structure of "germ-plasm"; while,
even apart from this consideration, there are at least three distinct
and highly general principles of specific change, which are accepted by
the great majority of Darwinists, and the only common peculiarity of
which is that they produce hereditary changes of specific types without
any reference to the principle of utility.
CHAPTER X.
CHARACTERS AS ADAPTIVE AND SPECIFIC
(_concluded_).
Our subject is not yet exhausted. For it remains to observe the
consequences which arise from the dogma of utility as the only _raison
d'etre_ of species, or of specific characters, when this dogma is
applied in practice by its own promoters.
* * * * *
Any definition of "species"--excepting Nos. 1, 2, and 5, which may here
be disregarded--must needs contain some such phrase as the one with
which Nos. 3 and 4 conclude. This is, that peculiar characters, in order
to be recognized as of specific value, must present neither more nor
less than "some certain degree of distinctness." If they present more
than this degree of distinctness, the form, or forms, in question must
be ranked as generic; while if they present less than this degree of
distinctness, they must be regarded as varietal--and this even if they
are known to be mutually sterile. What, then, is this certain degree of
distinctness? What are its upper and lower limits? This question is one
that cannot be answered. From the very nature of the case it is
impossible to find a uniform standard of distinction whereby to draw
our boundary lines between varieties and species on the one hand, or
between species and genera on the other. One or two quotations will be
sufficient to satisfy the general reader upon this point.
Mr. Wallace himself alludes to "the great difficulty that is felt by
botanists in determining the limits of species in many large genera,"
and gives as examples well-known instances where systematic botanists of
the highest eminence differ hopelessly in their respective estimates of
"specific characters." Thus:--
"Mr. Baker includes under a single species, Rosa canina, no less
than twenty-eight named varieties distinguished by more or less
constant characters, and often confined to special localities, and
to these are referred about seventy of the species of British and
continental botanists. Of the genus Rubus or bramble, five British
species are given in Bentham's _Handbook of British Flora_, while
in the fifth edition of Babington's _Manual of British Botany_,
published about the same time, no less than forty-five species are
described. Of willows (Salix) the same two works enumerate fifteen
and thirty-one species respectively. The hawkweeds (Hieracium) are
equally puzzling, for while Mr. Bentham admits only seven British
species, Professor Babington describes no less than seventy-two,
besides several named varieties[125]."
[125] _Darwinism_, p. 77.
Mr. Wallace goes on to quote further instances, such as that of Draba
verna, which Jordan has found to present, in the south of France alone,
no less than fifty-two permanent varieties, which all "come true from
seed, and thus present all the characteristics of a true species"; so
that, "as the plant is very common almost all over Europe, and ranges
from North America to the Himalayas, the number of similar forms over
this wide area would probably have to be reckoned by hundreds, if not by
thousands[126]."
[126] _Darwinism_, p. 77.
One or two further quotations may be given to the same general effect,
selected from the writings of specialists in their several departments.
"There is nothing that divides systematists more than what
constitutes a genus. Species that resemble each other more than
other species, is perhaps the best definition that can be given.
This is obviously an uncertain test, much depending on individual
judgement and experience; but that, in the evolution of forms, such
difficulties should arise in the limitation of genera and species
was inevitable. What is a generic character in one may be only a
specific character in another. As an illustration of the uncertain
importance of characters, I may mention the weevil genus
_Centrinus_ in which the leading characters in the classification
of the family to which it belongs are so mixed that systematists
have been content to keep the species together in a group that
cannot be defined.... No advantage or disadvantage is attached,
apparently, to any of the characters. There are about 200 species,
all American.
The venation of the wings of insects is another example of
modifications without serving any special purpose. There is no vein
in certain Thripidae, and only a rudiment or a single vein in
Chalcididae. There are thousands of variations more or less marked,
some of the same type with comparatively trivial variation, others
presenting distinct types, even in the same family, such genera,
for example, as _Polyneura_, _Tettigetra_, _Huechys_, &c. in the
Cicadidae.
Individual differences have often been regarded as distinctive of
species; varieties also are very deceptive, and races come very
near to species. A South-American beetle, _Arescus histrio_, has
varieties of yellow, red, and black, or these colours variously
intermixed, and, what is very unusual, longitudinal stripes in some
and transverse bars in others, and all taken in the same locality.
Mr. A. G. Butler, of the British Museum, is of opinion that 'what
is generally understood by the term species (that is to say, a
well-defined, distinct, and constant type, having no near allies)
is non-existent in the Lepidoptera, and that the nearest approach
to it in this order is a constant, though but slightly differing,
rare or local form--that genera, in fact, consist wholly of a
gradational series of such forms (Ann. Mag. Nat. Hist. 5, xix.
103)[127].'"
[127] Pascoe, _The Darwinian Theory of the Origin of Species_, 1891,
pp. 31-33, and 46.
So much as regards entomology, and still living forms. In illustration
of the same principles in connexion with palaeontological series, I may
quote Wuertenberger, who says:--
"With respect to these fossil forms [i.e. multitudinous forms of
fossil Ammonites], it is quite immaterial whether a very short or a
somewhat longer part of any branch be dignified with a separate
name, and regarded as a species. The prickly Ammonites, classed
under the designation of Armata, are so intimately connected that
it becomes impossible to separate the accepted species sharply from
one another. The same remark applies to the group of which the
manifold forms are distinguished by their ribbed shells, and are
called Planulata[128]."
[128] _Neuer Beitrag zum geologischen Beweis der Darwinischen
Theorie_, 1873.
I had here supplied a number of similar quotations from writers in
various other departments of systematic work, but afterwards struck them
out as superfluous. For it is not to be anticipated that any competent
naturalist will nowadays dispute that the terms "variety," "species,"
and "genus" stand for merely conventional divisions, and that whether a
given form shall be ranked under one or the other of them is often no
more than a matter of individual taste. From the nature of the case
there can be no objective, and therefore no common, standards of
delimitation. This is true even as regards any one given department of
systematic work; but when we compare the standards of delimitation which
prevail in one department with those which prevail in another, it
becomes evident that there is not so much as any attempt at agreeing
upon a common measure of specific distinction.
But what, it may well be asked, is the use of thus insisting upon
well-known facts, which nobody will dispute? Well, in the first place,
we have already seen, in the last chapter, that it is incumbent on those
who maintain that all species, or even all specific characters, must be
due to natural selection, to tell us what they mean by a species, or by
characters as specific. If I am told to believe that the definite
quality A is a necessary attribute of B, and yet that B is "not a
distinct entity," but an undefinable abstraction, I can only marvel that
any one should expect me to be so simple. But, without recurring to this
point, the use of insisting on the facts above stated is, in the second
place, that otherwise I cannot suppose any general reader could believe
them in view of what is to follow. For he cannot but feel that the cost
of believing them is to render inexplicable the mental processes of
those naturalists who, in the face of such facts, have deduced the
following conclusions.
The school of naturalists against which I am contending maintains, as a
generalization deduced from the theory of natural selection, that all
species, or even all specific characters, must necessarily owe their
origin to the principle of utility. Yet this same school does not
maintain any such generalization, either with regard to varietal
characters on the one hand, or to generic characters on the other. On
the contrary, Professor Huxley, Mr. Wallace, and all other naturalists
who agree with them in refusing to entertain so much as the abstract
possibility of any cause other than natural selection having been
productive of species, fully accept the fact of other causes having been
largely concerned in the production of varieties, genera, families, and
all higher groups, or of the characters severally distinctive of each.
Indeed, Mr. Wallace does not question what appears to me the extravagant
estimate of Professor Cope, that the non-adaptive characters distinctive
of those higher groups are fully equal, in point of numbers, to the
adaptive. But, surely, if the theory of evolution by natural selection
is, as we all agree, a true theory of the origin of species, it must
likewise be a true theory of the origin of genera; and if it be supposed
essential to the integrity of the theory in its former aspect that all
specific characters should be held to be useful, I fail to see how, in
regard to its latter aspect, we are so readily to surrender the
necessary usefulness of all generic characters. And exactly the same
remark applies to the case of constant "varieties," where again the
doctrine of utility as universal is not maintained. Yet, according to
the general theory of evolution, constant varieties are what Darwin
termed "incipient species," while species are what may be termed
"incipient genera." Therefore, if the doctrine of utility as universal
be conceded to fail in the case of varieties on the one hand and of
genera on the other, where is the consistency in maintaining that it
must "necessarily" hold as regards the intermediate division, species?
Truly the shade of Darwin may exclaim, "Save me from my friends." And
truly against logic of this description a follower of Darwin must find
it difficult to argue. If one's opponents were believers in special
creation, and therefore stood upon some definite ground while
maintaining this difference between species and all other taxonomic
divisions, there would at least be some issue to argue about. But when
on the one hand it is conceded that species are merely arbitrary
divisions, which differ in no respect as to the process of their
evolution from either varieties or genera, while on the other hand it is
affirmed that there is thus so great a difference in the result, all we
can say is that our opponents are entangling themselves in the meshes of
a sheer contradiction.
Or, otherwise stated, specific characters differ from varietal
characters in being, as a rule, more pronounced and more constant: on
this account advocates of utility as universal apply the doctrine to
species, while they do not feel the "necessity" of applying it to
varieties. But now, generic and all higher characters are even more
constant and more pronounced than specific characters--not to say, in
many cases, more generally diffused over a larger number of organisms
usually occupying larger areas. Therefore, _a fortiori_, if for the
reasons above stated evolutionists regard it as a necessary deduction
from the theory of natural selection that all specific characters must
be useful, much more ought it to be a necessary deduction from this
theory that all generic, and still more all higher, characters must be
useful. But, as we have seen, this is not maintained by our opponents.
On the contrary, they draw the sharpest distinction between specific and
all other characters in this respect, freely conceding that both those
below and those above them need not--and very often do not--present any
utilitarian significance.
Although it appears to me that this doctrine is self-contradictory, and
on this ground alone might be summarily dismissed, as it is now held in
one or other of its forms by many naturalists, I will give it a more
detailed consideration in both its parts--namely, first with respect to
the distinction between varieties and species, and next with respect to
the distinction between species and genera.
* * * * *
Until it can be shown that species are something more than merely
arbitrary divisions, due to the disappearance of intermediate varietal
links; that in some way or another they _are_ "definite entities," which
admit of being delineated by the application of some uniform or general
principles of definition; that, in short, species have only then been
classified as such when it has been shown that the origin of each has
been due to the operation of causes which have not been concerned in the
production of varieties;--until these things are shown, it clearly
remains a gratuitous dogma to maintain that forms which have been called
species differ from forms which have been called varieties in the
important respect, that they (let alone each of all their distinctive
characters) must necessarily have been due to the principle of utility.
Yet, as we have seen, even Mr. Wallace allows that a species is "not a
distinct entity," but "an assemblage of individuals which have become
somewhat modified in structure, form, and constitution"; while estimates
of the kinds and degrees of modification which are to be taken as of
specific value are conceded to be undefinable, fluctuating, and in not a
few cases almost ludicrously divergent.
Perhaps one cannot more forcibly present the rational value of this
position than by noting the following consequences of it. Mr. Gulick
writes me that while studying the land-shells of the Sandwich Islands,
and finding there a rich profusion of unique varieties, in cases where
the intermediate varieties were rare he could himself have created a
number of species by simply throwing these intermediate varieties into
his fire. Now it follows from the dogma which we are considering, that,
by so doing, not only would he have created new species, but at the same
time he would have proved them due to natural selection, and endowed the
diagnostic characters of each with a "necessarily" adaptive meaning,
which previously it was not necessary that they should present. Before
his destruction of these intermediate varieties, he need have felt
himself under no obligation to assume that any given character at either
end of the series was of utilitarian significance: but, after his
destruction of the intermediate forms, he could no longer entertain any
question upon the matter, under pain of being denounced as a Darwinian
heretic.
Now the application is self-evident. It is a general fact, which admits
of no denial, that the more our knowledge of any flora or fauna
increases, the greater is the number of intermediate forms which are
brought to light, either as still existing or as having once existed.
Consequently, the more that such knowledge increases, the more does our
catalogue of "species" diminish. As Kerner says, "bad species" are
always multiplying at the expense of "good species"; or, as Oscar
Schmidt (following Haeckel) similarly remarks, if we could know as much
about the latter as we do about the former, "all species, without any
exception, would become what species-makers understand by 'bad
species'[129]." Hence we see that, just as Mr. Gulick could have created
good species by secretly destroying his intermediate varieties, so has
Nature produced her "good species" for the delectation of systematists.
And just as Mr. Gulick, by first hiding and afterwards revealing his
intermediate forms, could have made the self-same characters in the
first instance necessarily useful, but ever afterwards presumably
useless, so has Nature caused the utility of diagnostic characters to
vary with our knowledge of her intermediate forms. It belongs to the
essence of our theory of descent, that in _all_ cases these intermediate
forms must either be now existing or have once existed; and, therefore,
that the work of species-makers consists in nothing more than marking
out the _lacunae_ in our knowledge of them. Yet we are bound to believe
that wherever these _lacunae_ in our knowledge occur, there occurs also
the objective necessity of causation as utilitarian--a necessity,
however, which vanishes so soon as our advancing information supplies
the intermediate forms in question. It may indeed appear strange that
the utility or non-utility of organic structures should thus depend on
the accidents of human knowledge; but this is the Darwinian faith, and
he who doubts the dogma is to be anathema.
[129] _The Doctrine of Descent and Darwinism_, Eng. Trans. p. 102.
Turning next to the similar distinction which it is sought to draw
between species and genera, here it will probably be urged, as I
understand it to be urged by Mr. Wallace, that generic characters (and
still more characters of families, orders, &c.) refer back to so remote
a state of things that utility may have been present at their birth
which has disappeared in their maturity. In other words, it is held that
all generic characters were originally specific characters; that as such
they were all originally of use; but that, after having been rendered
stable by heredity, many of them may have ceased to be of service to the
descendants of those species in which they originated, and whose
extinction has now made it impossible to divine what that service may
have been.
Now, in the first place; this is not the interpretation adopted by
Darwin. For instance, he expressly contrasts such cases with those of
vestigial or "rudimentary" structures, pointing out that they differ
from vestigial structures in respect of their permanence. One quotation
will be sufficient to establish the present point.
"A structure which has been developed through long-continued
selection, when it ceases to be of service to a species, generally
becomes variable, as we see with rudimentary organs, for it will no
longer be regulated by this same power of selection. But when, from
the nature of the organism and of the conditions, modifications
have been induced which are unimportant for the welfare of the
species, they may be, and apparently often have been, transmitted
in nearly the same state to numerous, otherwise modified,
descendants[130]."
[130] _Origin of Species_, p. 175.
Here, and in the context, we have a sufficiently clear statement of
Darwin's view--first, that unadaptive characters may arise in _species_
as "fluctuating variations, which sooner or later become _constant_
through the nature of the organism and of surrounding conditions, as
well as through the intercrossing of distinct individuals, but _not_
through natural selection"[131]; second, that such unadaptive characters
may then be transmitted in this their stable condition to
species-progeny, so as to become distinctive of genera, families, &c.;
third, that, on account of such characters not being afterwards liable
to diverse adaptive modifications in different branches of the
species-progeny, they are of more value as indicating lines of pedigree
than are characters which from the first have been useful; and, lastly,
they are therefore now empirically recognized by systematists as of most
value in guiding the work of classification. To me it appears that this
view is not only perfectly rational in itself, but likewise fully
compatible with the theory of natural selection--which, as I have
previously shown, is _primarily_ a theory of adaptive characters, and
therefore not necessarily a theory of _all_ specific characters. But to
those who think otherwise, it must appear--and does appear--that there
is something wrong about such a view of the case--that it was not
consistent in the author of the _Origin of Species_ thus to refer
non-adaptive generic characters to a parentage of non-adaptive specific
characters. Nevertheless, as a matter of fact, Darwin was perfectly
consistent in putting forth this view, because, unlike Wallace, he was
not under the sway of any antecedent dogma erroneously deduced from the
theory of natural selection.
[131] _Ibid._ p. 176: italics mine.
Next without reference to Darwin's authority, let us see for ourselves
where the inconsistency really lies. To allow that generic characters
may be useless, while denying that specific characters can ever be so
(unless correlated with others that are useful), involves an appeal to
the argument from ignorance touching the ancestral habits,
life-conditions, &c., of a parent species now extinct. Well, even upon
this assumption of utility as obsolete, there remains to be explained
the "stability" of useless characters now distinctive of genera,
families, orders, and the rest. We know that specific characters which
have owed their origin to utility and have afterwards ceased to present
utility, degenerate, become variable, inconstant, "rudimentary," and
finally disappear. Why, then, should these things not happen with regard
to useless generic distinctions? Still more, why should they not happen
with regard to family, ordinal, and class distinctions? On the lines
against which I am arguing it would appear impossible that any answer to
this question can be suggested. For what explanation can be given of the
contrast thus presented between the obsolescence of specific characters
where previous utility is demonstrable, and the permanence of higher
characters whose previous utility is assumed? As we have already seen,
Mr. Wallace himself employs this consideration of permanence and
constancy against the view that any cause other than natural selection
can have been concerned in the origin and maintenance of _specific_
characters. But he does not seem to see that the consideration cuts two
ways--and much more forcibly against his views than in favour of them.
For while, as already shown in the chapter before last, it is
sufficiently easy to dispose of the consideration as Wallace uses it (by
simply pointing out with Darwin that any causes other than natural
selection which may have been concerned in the genesis of _specific_
characters, must, if equally uniform in their operation, equally give
rise to permanence and constancy in their results); on the other hand,
it becomes impossible to explain the stability of useless _generic_
characters, if, as Wallace's use of the argument requires, natural
selection is the only possible cause of stability. The argument is one
that cannot be played with fast and loose. Either utility is the sole
condition to the stability of _any_ diagnostic character (in which case
it is not open to Mr. Wallace to assume that all _generic_ or higher
characters which are now useless have owed their origin to a past
utility); or else utility is not the sole condition to stability (in
which case his use of the present argument in relation to _specific_
characters collapses). We have seen, indeed, in the chapter before last,
that his use of the argument collapses anyhow, or quite irrespective of
his inconsistent attitude towards generic characters, with which we were
not then concerned. But the point now is that, as a mere matter of
logic, the argument from stability as Wallace applies it to the case of
specific characters, is incompatible with his argument that useless
generic characters may originally have been useful specific characters.
It can scarcely be questioned that the transmutation of a species into a
genus must, as a rule, have allowed time enough for a newly
acquired--i.e. peculiar specific-character--to show some signs of
undergoing degeneration, if, as supposed, the original cause of its
development and maintenance was withdrawn when the parent species began
to ramify into its species-progeny. Yet, as Darwin says, "it is
notorious that specific characters are more variable than generic[132]."
So that, upon the whole, I do not see how on grounds of general
reasoning it is logically possible to maintain Mr. Wallace's distinction
between specific and generic characters in respect of necessary utility.
[132] _Origin of Species_, p. 122.
But now, and lastly, we shall reach the same conclusion if, discarding
all consideration of general principles and formal reasoning, we fasten
attention upon certain particular cases, or concrete facts. Thus, to
select only two illustrations within the limits of genera, it is a
diagnostic feature of the genus _Equus_ that small warty callosities
occur on the legs. It is impossible to suggest any useful function that
is now discharged by these callosities in any of the existing species of
the genus. If it be assumed that they must have been of some use to the
species from which the genus originally sprang, the assumption, it seems
to me, can only be saved by further assuming that in existing species of
the genus these callosities are in a vestigial condition--i. e. that in
the original or parent species they performed some function which is
now obsolete. But against these assumptions there lies the following
fact. The callosities in question are not similarly distributed through
all existing species of the genus. The horse has them upon all his four
legs, while other species have them only upon two. Therefore, if all
specific characters are necessarily due to natural selection, it is
manifest that these callosities are _not_ now vestigial: on the
contrary, they _must_ still be--or, at best, have recently been--of so
much importance to all existing species of the genus, that not only is
it a matter of selection-value to all these species that they should
possess these callosities; but it is even a matter of selection-value to
a horse that he should possess four of them, while it is equally a
matter of selection-value to the ass that he should possess only two.
Here, it seems to me, we have once more the doctrine of the necessary
utility of specific characters reduced to an absurdity; while at the
same time we display the incoherency of the distinction between specific
characters and generic characters in respect of this doctrine. For the
distinction in such a case amounts to saying that a generic character,
if evenly distributed among all the species, need not be an adaptive
character; whereas, if any one of the species presents it in a slightly
different form, the character must be, on this account, necessarily
adaptive. In other words, the uniformity with which a generic character
occurs among the species of the genus is taken to remove that character
from the necessarily useful class, while the absence of such uniformity
is taken as proof that the character must be placed within the
necessarily useful class. Which is surely no less a _reductio ad
absurdum_ with regard to the generic character than the one just
presented with regard to its variants as specific characters. And, of
course, this twofold absurdity is presented in all cases where a generic
character is unequally distributed among the constituent species of a
genus.
[Illustration: Fig. 4.--Lower Teeth of Orang (after Tomes).]
But here is an illustration of another class of cases. Mr. Tomes has
shown that the molar teeth of the Orang present an extraordinary and
altogether superfluous amount of attachment in their sockets--the fangs
being not only exceedingly long, and therefore deeply buried in the
jaw-bone, but also curving round one another, so as still further to
strengthen the whole[133]. In the allied genera of anthropoid apes there
is no such abnormal amount of attachment. Now, the question is, of what
conceivable use can it _ever_ have been, either to the existing genus,
or to its parent species, that such an abnormal amount of attachment
should obtain? It certainly is not required to prevent dislocation of
the teeth, seeing that in all allied genera, and even in man himself,
the amount of attachment is already so great that teeth will break
before they can be drawn by anything short of a dentist's forceps.
Therefore I conclude that this peculiarity in the dentition of the genus
must have arisen in its parent species by way of what Darwin calls a
"fluctuating variation," without utilitarian significance. And I adduce
it in the present connexion because the peculiarity is one which is
equally unamenable to a utilitarian explanation, whether it happens to
occur as a generic or a specific character.
[133] _A Manual of Dental Anatomy_, p. 455.
Numberless similar cases might be quoted; but probably enough has now
been said to prove the inconsistency of the distinction which our
opponents draw between specific and all higher characters in respect of
utility. In point of fact, a very little thought is enough to show that
no such distinction admits of being drawn; and, therefore, that any one
who maintains the doctrine of utility as universal in the case of
specific characters, must in consistency hold to the same doctrine in
the case of generic and all higher characters. And the fact that our
opponents are unable to do this becomes a virtual confession on their
part of the futility of the generalization which they have
propounded[134].
[134] It may be observed that this distinction was not propounded by
Mr. Wallace--nor, so far as I am aware, by anybody else--until
he joined issue with me on the subject of specific characters.
Whether he has always held this important distinction between
specific and generic characters, I know not; but, as
originally enunciated, his doctrine of utility as universal
was subject to no such limitation: it was stated
unconditionally, as applying to all taxonomic divisions
indifferently. The words have already been quoted on page 180;
and, if the reader will turn to them, he may further observe
that, prior to our discussion, Mr. Wallace made no allowance
for the principle of correlation, which, as we have seen,
furnishes so convenient a loop-hole of escape in cases where
even the argument from our ignorance of possible utility
appears absurd. In his latest work, however, he is much less
sweeping in his statements. He limits his doctrine to the case
of "specific characters" alone, and even with regard to them
makes unlimited drafts upon the principle of correlation.
On what then do Mr. Wallace and his followers rely for their great
distinction between specific and all other characters in respect of
utility? This is the final and fundamental question which I must leave
these naturalists themselves to answer; for my whole contention is, that
it is unanswerable. But although I am satisfied that they have nothing
on which to base their generalization, it seems worth while to conclude
by showing yet one further point. And this is, that these naturalists
themselves, as soon as they quit merely abstract assertions and come to
deal with actual facts, contradict their own generalization. It is worth
while to show this by means of a few quotations, that we may perceive
how impossible it is for them to sustain their generalization in the
domain of fact.
As it is desirable to be brief, I will confine myself to quoting from
Mr. Wallace.
"Colour may be looked upon as a necessary result of the highly
complex chemical constitution of animal tissues and fluids. The
blood, the bile, the bones, the fat, and other tissues have
characteristic, and often brilliant colours, which we cannot
suppose to have been determined for any special purpose as colours,
since they are usually concealed. The external organs and
integuments, would, by the same general laws, naturally give rise
to a greater variety of colour[135]."
[135] _Darwinism_, p. 297.
Surely comment is needless. Have the colour of external organs and
integuments nothing to do with the determining of specific distinctions
by systematists? Or, may we not rather ask, are there any other
"characters" which have had more to do with their delineation of animal
species? Therefore, if "the external organs and integuments naturally
give rise to a greater variety of colours," for non-utilitarian reasons,
than is the case with internal organs and tissues; while even the latter
present, for similarly non-utilitarian reasons, such variety and
intensity of colours as they do; must it not follow that, on the ground
of the "Laws of Growth" alone, Mr. Wallace has conceded the entire case
as regards "a large proportional number of specific characters" being
non-adaptive--"spontaneous" in their occurrence, and "meaningless" in
their persistence?
Once more:--
"The enormously lengthened plumes of the bird of paradise and of
the peacock, can, however, have no such use [i.e. for purposes of
defence], but must be rather injurious than beneficial in the
birds' ordinary life. The fact that they have been developed to so
great an extent in a few species is an indication of such perfect
adaptation to the conditions of existence, such complete success in
the battle for life, that there is, in the adult male at all
events, a surplus of strength, vitality, and growth-power, which is
able to expend itself in this way without injury. That such is the
case is shown by the great abundance of most of the species which
possess these wonderful superfluities of plumage.... Why, in allied
species, the development of accessory plumes has taken different
forms, we are unable to say, except that it may be due to that
individual variability which has served as a starting-point for so
much of what seems to us strange in form, or fantastic in colour,
both in the animal and vegetable world[136]."
[136] _Darwinism_, pp. 292-3.
Here, again, one need only ask, How can such statements be reconciled
with the great dogma, "which is indeed a necessary deduction from the
theory of Natural Selection, namely, that none of the definite facts of
organic nature, no special organ, no characteristic form or marking can
exist, but which must now be, or once have been, _useful_"? Can it be
said that the plumes of a bird of paradise present "no characteristic
form," or the tail of a peacock "no characteristic marking"? Can it be
held that all the "fantastic colours," which Darwin attributes to sexual
selection, and all the "strange forms" in the vegetable world which
present no conceivable reference to adaptation, are to be ascribed to
"individual variability" without reference to utility, while at the same
time it is held, "as a necessary deduction from the theory of Natural
Selection," that _all_ specific characters must be "_useful_"? Or must
we not conclude that we have here a contradiction as direct as a
contradiction can well be[137]?
[137] Since the above was written both Mr. Gulick and Professor
Lloyd Morgan have independently noticed the contradiction.
Nor is it any more possible to reconcile these contradictory statements
by an indefinite extension of the term "correlation," than we found it
to be in the cases previously quoted. It might indeed be logically
possible, howsoever biologically absurd, to attribute the tail of a
peacock--with all its elaboration of structure and pattern of colour,
with all the drain that its large size and weight makes upon the vital
resources of the bird, with all the increased danger to which it exposes
the bird by rendering it more conspicuous, more easy of capture, &c.--to
correlation with some useful character peculiar to peacocks. But to say
that it is due to correlation with general "vitality," is merely to
discharge the doctrine of correlation of any assignable meaning.
Vitality, or "perfect adaptation to the conditions of existence," is
obviously a prime condition to the occurrence of a peacock's tail, as it
is to the occurrence of a peacock itself; but this is quite a different
thing from saying that the specific characters which are presented by a
peacock's tail, although useless in themselves, are correlated with some
other and useful specific characters of the same bird--as we saw in a
previous chapter with reference to secondary sexual characters in
general. Therefore, when Mr. Wallace comes to the obvious question why
it is that even in "allied species," which must be in equally "perfect
adaptation to the conditions of existence," there are no such "wonderful
superfluities of plumage," he falls back--as he previously fell back--on
whatever unknown _causes_ it may have been which produced the peacock's
tail, when the primary _condition_ to their operation has been furnished
by "complete success in the battle for life."
I have quoted the above passages, not so much for the sake of exposing
fundamental inconsistencies on the part of an adversary, as for the sake
of observing that they constitute a much truer exposition of "Darwinism"
than do the contradictory views expressed in some other parts of the
work bearing that title. For even if characters of so much size and
elaboration as the tail of a peacock, the plumes of a bird of paradise
&c., are admitted to be due to non-utilitarian causes, much more must
innumerable other characters of incomparably less size and elaboration
be mere "superfluities." Without being actually deleterious, "a large
proportional number of specific characters," whose utility is not
apparent, must _a fortiori_ have been due to "individual variation," to
"general laws which determine the production" of such characters--or, in
short, to some causes other than natural selection. And this, I say, is
a doctrine much more in harmony with "Darwinism" than is the
contradictory doctrine which I am endeavouring to resist.
But once again, and still more generally, after saying of "the delicate
tints of spring foliage, and the intense hues of autumn," that "as
colours they are unadaptive, and appear to have no more relation to the
well-being of plants themselves than do the colours of gems and
minerals," Mr. Wallace proceeds thus:--
"We may also include in the same category those algae and fungi
which have bright colours--the red snow of the Arctic regions, the
red, green, or purple seaweeds, the brilliant scarlet, yellow,
white or black agarics, and other fungi. All these colours are
probably the direct results of chemical composition or molecular
structure, and being thus normal products of the vegetable
organism, need no special explanation from our present point of
view; and the same remark will apply to the varied tints of the
bark of trunks, branches and twigs, which are often of various
shades of brown and green, or even vivid reds and yellows[138]."
[138] _Darwinism_, p. 302.
Here, as Mr. Gulick has already observed, "Mr. Wallace seems to admit
that instead of useless specific characters being unknown, they are so
common and so easily explained by 'the chemical constitution of the
organism' that they claim no special attention[139]." And whatever
answer Mr. Wallace may make to this criticism, I do not see how he is to
meet the point at present before us--namely, that, upon his own showing,
there are in nature numberless instances of "characters which are
useless without being hurtful," and which nevertheless present absolute
"constancy." If, in order to explain the contradiction, he should fall
back upon the principle of correlation, the case would not be in any way
improved. For, here again, if the term correlation were extended so as
to include "the chemical constitution or the molecular structure of the
organism," it would thereby be extended so as to discharge all Darwinian
significance from the term.
[139] _American Journal of Science_, Vol. XL. art. I. on _The
Inconsistencies of Utilitarianism as the Exclusive Theory of
Organic Evolution_.
_Summary._
I will conclude this discussion of the Utility question by
recapitulating the main points in an order somewhat different from that
in which they have been presented in the foregoing chapters. Such a
variation may render their mutual connexions more apparent. But it is
only to the main points that allusion will here be made, and, in order
the better to show their independent character, I will separately number
them.
* * * * *
1. The doctrine of utility as universal, whether with respect to species
only or likewise with respect to specific characters, is confessedly an
_a priori_ doctrine, deduced by way of general reasoning from the theory
of natural selection.
2. Being thus founded exclusively on grounds of deduction, the doctrine
cannot be combated by any appeal to facts. For this question is not one
of fact: it is a question of reasoning. The treatment of our subject
matter is logical: not biological.
3. The doctrine is both universal and absolute. According to one form of
it _all_ species, and according to another form of it _all_ specific
characters, must _necessarily_ be due to the principle of utility.
4. The doctrine in both its forms is deduced from a definition of the
theory of natural selection as a theory, and the sole theory, of the
origin of _species_; but, as Professor Huxley has already shown, it does
not really follow, even from this definition, that all specific
_characters_ must be "necessarily useful." Hence the two forms of the
doctrine, although coincident with regard to species, are at variance
with one another in respect of specific characters. Thus far, of course,
I agree with Professor Huxley; but if I have been successful in showing
that the above definition of the theory of natural selection is
logically fallacious, it follows that the doctrine in both its forms is
radically erroneous. The theory of natural selection is not, accurately
speaking, a theory of the origin of species: it is a theory of the
origin and cumulative development of adaptations, to whatever order of
taxonomic division these may happen to belong. Thus the premisses of the
deduction which we are considering collapse: the principle of utility is
shown not to have any other or further reference to species, or to
specific characters, than it has to fixed varieties, genera, families,
&c., or to the characters severally distinctive of each.
5. But, quitting all such antecedent considerations, we next proceeded
to examine the doctrine _a posteriori_, taking the arguments which have
been advanced in favour of the doctrine, other than those which rest
upon the fallacious definition. These arguments, as presented by Mr.
Wallace, are two in number.
First, it is represented that natural selection must occupy the whole
field, because no other principle of change can be allowed to operate in
the presence of natural selection. Now I fully agree that this statement
holds as regards any principle of change which is deleterious, but I
cannot agree that it does so as regards any such principle which is
merely neutral. No reason has ever been shown why natural selection
should interfere with "indifferent" characters--to adopt Professor
Huxley's term--supposing such to have been produced by any of the
agencies which we shall presently have to name. Therefore this
argument--or rather assertion--goes for nothing.
Mr. Wallace's second argument is, that utility is the only principle
which can endow specific characters with their characteristic stability.
But this again is mere assertion. Moreover, it is assertion opposed
alike to common sense and to observable fact. It is opposed to common
sense, because it is obvious that any other principle would equally
confer stability on characters due to it, provided that its action is
constant, as Darwin expressly held. Again, this argument is opposed to
fact, because we know of thousands of cases where peculiar characters
are stable, which, nevertheless, cannot possibly be due to natural
selection. Of such are the Porto Santo rabbits, the niata cattle, the
ducks in St. James' Park, turkeys, dogs, horses, &c., and, in the case
of plants, wheat, cabbage, maize, &c., as well as all the hosts of
climatic varieties, both of animals and plants, in a state of nature.
Indeed, on taking a wide survey of the facts, we do not find that the
principle of utility is any better able to confer stability of character
than are many other principles, both known and unknown. Nay, it is
positively less able to do so than are some of these other principles.
Darwin gives two very probable reasons for this fact; but I need not
quote them a second time. It is enough to have seen that this argument
from stability or constancy is no less worthless than the previous one.
Yet these are the only two arguments of a corroborative kind which Mr.
Wallace adduces whereby to sustain his "necessary deduction."
6. At this point, therefore, it may well seem that we need not have
troubled ourselves any further with a generalization which does not
appear to have anything to support it. And to this view of the case I
should myself agree, were it not that many naturalists now entertain the
doctrine as an essential article of their Darwinian creed. Hence, I
proceeded to adduce considerations _per contra_.
Seeing that the doctrine in question can only rest on the assumption
that there is no cause other than natural selection which is capable of
originating any single species--if not even so much as any single
specific character--I began by examining this assumption. It was shown
first that, on merely antecedent grounds, the assumption is "infinitely
precarious." There is absolutely no justification for the statement that
in all the varied and complex processes of organic nature natural
selection is the only possible cause of specific change. But, apart
altogether from this _a priori_ refutation of the dogma, our analysis
went on to show that, in point of actual fact, there are not a few
well-known causes of high generality, which, while having no connexion
with the principle of utility, are demonstrably capable of originating
species and specific characters--if by "species" and "specific
characters" we are to understand organic types which are ranked as
species, and characters which are described as diagnostic of species.
Such causes I grouped under five different headings, viz. Climate, Food,
Sexual Selection, Isolation, and Laws of Growth. Sexual Selection and
Isolation are, indeed, repudiated by Mr. Wallace; but, in common I
believe with all biologists, he accepts the other three groups of causes
as fully adequate to produce such kinds and degrees of modification as
are taken to constitute specific distinction. And this is amply
sufficient for our present purposes. Besides, under the head of Sexual
Selection, it does not signify in the present connexion whether or not
we accept Darwin's theory on this subject. For, in any case, the facts
of secondary sexual characters are indisputable: these characters are,
for the most part, specific characters: and they cannot be explained by
the principle of utility. Even Mr. Wallace does not attempt to do so;
and the explanation which he does give is clearly incompatible with his
doctrine touching the necessarily life-serving value of all specific
characters. Lastly, the same has to be said of the Laws of Growth. For
we have just seen that on the grounds of this principle likewise Mr.
Wallace abandons the doctrine in question. As regards Isolation, much
more remains to be said in the ensuing portion of this work, while, as
regards Climatic Variation, there are literally innumerable cases where
changes of specific type are known to have been caused by this means.
7. To the latter class of cases, however, it will be objected that these
changes of specific type, although no doubt sufficiently "stable" so
long as the changed conditions remain constant, are found by experiment
not to be hereditary; and this clearly makes all the difference between
a true specific change and a merely fictitious appearance of it.
Well, in the first place, this objection can have reference only to the
first two of the five principles above stated. It can have no reference
to the last three, because of these heredity constitutes the very
foundation. This consideration ought to be borne in mind throughout. But
now, in the second place, even as regards changes produced by climate
and food, the reply is nugatory. And this for three reasons, as follows.
(_a_) No one is thus far entitled to conclude against the possible
transmission of acquired characters; and, so long as there is even so
much as a possibility of climatic (or any other admittedly
non-utilitarian) variations becoming in this way hereditary, the reply
before us merely begs the question.
(_b_) Even supposing, for the sake of argument, that acquired characters
can never in any case become congenital, there remains the strong
probability--sanctioned as such even by Weismann--that changed
conditions of life may not unfrequently act upon the material of
heredity itself, thus giving rise to specific changes which are from
the first congenital, though not utilitarian. Indeed, there are not a
few facts (Hoffmann's plants, Weismann's butterflies, &c.), which can
only be explained either in this way, or as above (_a_). And in the
present connexion it is immaterial which of these alternative
explanations we choose to adopt, seeing that they equally refute our
opponents' objection. And not only do these considerations--(_a_) and
(_b_)--refute this particular objection; they overturn on new and
independent grounds the whole of our opponents' generalization. For the
generalization is, that the principle of utility, acting through natural
selection, is "necessarily" the sole principle which can be concerned in
hereditary changes of specific type. But here we perceive both a
possibility (_a_) and a probability (_b_), if not indeed a certainty,
that quite other principles have been largely concerned in the
production of such changes.
(_c_) Altogether apart from these considerations, there remains a much
more important one. For the objection that fixed--or "stable"--climatic
varieties differ from true species in not being subject to heredity,
raises the question--What are we to understand by a "species"? This
question, which was thus far purposely left in abeyance, had now to be
dealt with seriously. For it would clearly be irrational in our
opponents to make this highly important generalization with regard to
species and specific characters, unless they are prepared to tell us
what they mean by species, and therefore by characters as specific. In
as far as there is any ambiguity on this point it makes entirely for
our side in the debate, because even any small degree of uncertainty
with regard to it would render the generalization in question
proportionally unsound. Yet it is notorious that no word in existence is
more vague, or more impossible to define, than the word "species." The
very same men who at one time pronounce their great generalization with
regard to species, at another time asseverate that "a species is not a
definite entity," but a merely abstract term, serving to denote this
that and the other organic type, which this that and the other
systematist regards as deserving such a title. Moreover it is
acknowledged that systematists differ among themselves to a wide extent
as to the kinds and degrees of peculiarity which entitle a given form to
a specific rank. Even in the same department of systematic work much
depends on merely individual taste, while in different departments
widely different standards of delimination are in vogue. Hence, our
_reductio ad absurdum_ consists in this--that whether a given form is to
be regarded as necessarily due to natural selection, and whether all its
distinctive characters are to be regarded as necessarily utilitarian
characters, will often depend on whether it has been described by
naturalist A or by naturalist B. There is no one criterion--there is not
even any one set of criteria--agreed upon by naturalists for the
construction of specific types. In particular, as regards the principle
of heredity, it is not known of one named species in twenty--probably
not in a hundred--whether its diagnostic characters are hereditary
characters; while, on the other hand, even in cases where experiment has
proved "constant varieties" to be hereditary--and even also
cross-sterile with allied varieties--it is only some three or four
living botanists who for these reasons advocate the elevation of such
varieties to the rank of species. In short, as we are not engaged on any
abstract question touching the principles on which species ought to have
been constituted by their makers, but upon the actual manner in which
they have been, the criterion of heredity must needs be disregarded in
the present discussion, as it has been in the work of systematists. And
the result of this is, that any objection to our introducing the facts
of climatic variation in the present discussion is excluded. In
particular, so far as any question of heredity is concerned, all these
facts are as assuredly as they are cogently relevant. It is perfectly
certain that there is "a large proportional number" of named
species--particularly of plants--which further investigation would
resolve into climatic varieties. With the advance of knowledge, "bad
species" are always increasing at the expense of "good species," so that
we are now justified in concluding with Kerner, Haeckel, and other
naturalists best qualified to speak on this subject, that if we could
know as much about the past history and present relations of the
remaining good species as we do about the bad, all the former, without
exception, would become resolved into the latter. In point of fact, and
apart altogether from the inductive experience on which this conclusion
is based, the conclusion follows "as a necessary deduction" from the
general theory of descent. For this theory essentially consists in
supposing either the past or the present existence of intermediate
varietal forms in all cases, with the consequence that "good species"
serve merely to mark _lacunae_ in our knowledge of what is everywhere a
finely graduated process of transmutation. Hence, if we place this
unquestionably "necessary deduction" from the general theory of descent
side by side with the alleged "necessary deduction" from the theory of
natural selection, we cannot avoid the following absurdity--Whether or
not a given form is to be regarded as necessarily due to natural
selection, and all its characters necessarily utilitarian, is to be
determined, and determined solely, by the mere accident of our having
found, or not having found, either in a living or in a fossil state, its
varietal ancestry.
8. But this leads us to consider the final and crowning incongruities
which have been dealt with in the present chapter. For here we have
seen, not only that our opponents thus draw a hard and fast line between
"varieties" and "species" in regard to "necessary origin" and "necessary
utility," but that they further draw a similar line between "species"
and "genera" in the same respects. Yet, in accordance with the general
theory of evolution, it is plainly as impossible to draw any such line
in the one case as it is to do so in the other. Just as fixed varieties
are what Darwin called "incipient species," so are species incipient
genera, genera incipient families, and so on. Evolutionists must believe
that the process of evolution is everywhere the same. Nevertheless,
while admitting all this, the school of Huxley contradicts itself by
alleging some unintelligible exception in the case of "species," while
the school of Wallace presses this exception so as to embrace "specific
characters." Indeed Mr. Wallace, while maintaining that all specific
characters must necessarily be useful, maintains at the same time that
any number of varietal characters on the one hand, and a good half of
generic characters on the other, are probably useless. Thus he
contradicts his argument from the "constancy of specific characters"
(seeing that generic characters are still more constant), as later on we
saw that he contradicts his deductive generalization touching their
necessary utility, by giving a non-utilitarian explanation of whole
multitudes of specific characters. I need not, however, again go over
the ground so recently traversed; but will conclude by once more
recurring to the only explanation which I have been able to devise of
the otherwise inexplicable fact, that in regard to this subject so many
naturalists still continue to entangle themselves in the meshes of
absurdity and contradiction.
* * * * *
The only conceivable explanation is, that these naturalists have not yet
wholly divested themselves of the special creation theory. Although
professing to have discarded the belief that "species" are "definite
entities," differing in kind from "varieties" on the one hand and from
"genera" on the other, these writers are still imbued with a vague
survival of that belief. They well know it to belong to the very essence
of their new theory that "species" are but "pronounced varieties," or,
should we prefer it, "incipient genera"; but still they cannot
altogether escape the pre-Darwinian conception of species as organic
units, whose single mode of origin need not extend to other taxonomic
groups, and whose characters therefore present some exceptional
significance to the scientific naturalist. So to speak, such divinity
doth still hedge a species, that even in the very act of declaring it
but an idol of their own creation, these naturalists bow before their
fetish as something that is unique--differing alike in its origin and in
its characters from the varieties beneath and the genera above. The
consequence is that they have endeavoured to reconcile these
incompatible ideas by substituting the principle of natural selection
for that of super-natural creation, where the particular case of
"species" is concerned. In this way, it vaguely seems to them, they are
able to save the doctrine of some one mode of origin as appertaining to
species, which need not "necessarily" appertain to any other taxonomic
division. All other such divisions they regard, with their pre-Darwinian
forefathers, as merely artificial constructions; but, likewise with
these forefathers, they look upon species as natural divisions, proved
to be such by a single and necessary mode of origin. Hence, Mr. Wallace
expressly defines a species with reference to this single and necessary
mode of origin (_see_ above, p. 235), although he must be well aware
that there is no better, or more frequent, proof of it in the case of
species, than there is in that of somewhat less pronounced types on the
one hand (fixed varieties), or of more pronounced types on the other
(genera, families, &c.). Hence, also, the theory of natural selection is
defined as _par excellence_ a theory of the origin of species; it is
taken as applying to the particular case of the origin of species in a
peculiarly stringent manner, or in a manner which does not apply to the
origin of any other groups. And I believe that an important accessory
reason of the continuance of this view for more than thirty years after
the publication of the _Origin of Species by means of Natural
Selection_, is to be found in the title of that work. "Natural
Selection" has thus become verbally associated with "Origin of Species,"
till it is thoughtlessly felt that, in some way or another, natural
selection must have a peculiar reference to those artificially
delineated forms which stand anywhere between a fixed variety and a
so-called genus. This verbal association has no doubt had the effect of
still further preserving the traditional halo of mystery which clings to
the idea of a "species." Hence it comes that the title which Darwin
chose--and, looking to the circumstances of the time, wisely chose--for
his great work, has subsequently had the effect of fostering the very
idea which it was the object of that work to dissipate, namely, that
species are peculiar entities, which differ more or less in origin or
kind from all other taxonomic groups. The full title of this work
is--_The Origin of Species by means of Natural Selection: or the
Preservation of Favoured Races in the Struggle for Life_. Now, supposing
that instead of this its author had chosen some such title as the
following:--_The Origin of Organic Types by means of Adaptive Evolution:
or Survival of the Fittest Forms in the Struggle for Life_. Of course
this would have been a bad substitute from various points of view; but
could any objection have been urged against it from our present point of
view? I do not see that there could. Yet, if such had been the title, I
have little doubt that we should never have heard of those great
generalizations with regard to species and specific characters, the
futility of which it has been the object of these chapters to expose.
* * * * *
In conclusion, it only remains to reiterate that in thus combating what
appears to me plainly erroneous deductions from the theory of natural
selection, I am in no wise combating that theory itself. On the
contrary, I hope that I am rendering it no unimportant service by
endeavouring to relieve it of a parasitic growth--an accretion of false
logic. Regarding as I do the theory of natural selection as, primarily,
a theory of the origin (or cumulative development) of adaptations, I see
in merely non-adaptive characters--be they "specific" or other--a
comparatively insignificant class of phenomena, which may be due to a
great variety of incidental causes, without any further reference to the
master-principle of natural selection than that in the presence of this
principle none of these non-adaptive characters can be actively
deleterious. But that there may be "any number of indifferent
characters" it is no part of the theory of natural selection to deny;
and all attempts to foist upon it _a priori_ "deductions" opposed alike
to the facts of nature and to the logic of the case, can only act to the
detriment of the great generalization which was expressly guarded from
such fallacies by the ever-careful judgement of Darwin.
APPENDICES AND NOTES
APPENDIX I.
ON PANMIXIA.
There are several points of considerable theoretical importance
connected with Panmixia, which were omitted from the text, in order to
avoid distracting attention from the main issue which is there under
consideration. These side issues may now be appropriately presented in
the form in which they were published in _Nature_, March 13, 1890[140].
After stating, in almost the same words, what has already been said in
Chapter X, this paper proceeds, with the exception of a few verbal
alterations, as follows.
[140] Vol. xli. p. 438.
"There is, however, one respect in which Professor Weismann's
statement of the principle of panmixia differs from that which was
considered by Mr. Darwin; and it is this difference of
statement--which amounts to an important difference of theory--that
I now wish to discuss.
"The difference in question is, that while Professor Weismann
believes the cessation of selection to be capable of inducing
degeneration down to the almost complete disappearance of a
rudimentary organ, I have argued that, _unless assisted by some
other principle_, it can at most only reduce the degenerating organ
to considerably above one-half its original size--or probably not
through so much as one-quarter. The ground of this argument (which
is given in detail in the _Nature_ articles of 1873-1874) is, that
panmixia depends for its action upon fortuitous variations round an
ever-diminishing average--the average thus diminishing because it
is no longer _sustained_ by natural selection. But although no
longer sustained by _natural selection_, it does continue to be
sustained by _heredity_; and therefore, as long as the force of
heredity persists unimpaired, fortuitous variations alone--or
variation which is no longer controlled by natural
selection--cannot reduce the dwindling organ to so much as one-half
of its original size; indeed, as above foreshadowed, the balance
between the positive force of heredity and the negative effects of
promiscuous variability will most likely be arrived at above the
middle line thus indicated. Only if for any reason the force of
heredity begins to fail can the average round which the cessation
of selection works become a progressively diminishing average. In
other words, so long as the original force of heredity as regards
the useless organ remains unimpaired, the mere withdrawal of
selection cannot reduce the organ much below the level of
efficiency above which it was previously _maintained_ by the
_presence_ of selection. If we take this level to be 80 or 90 per
cent. of the original size, cessation of selection will reduce the
organ through the 10 or 20 per cent., and there leave it
fluctuating about this average, unless for any reason the force of
heredity begins to fail--in which case, of course, the average will
progressively fall in proportion to the progressive weakening of
this force.
"Now, according to my views, the force of heredity under such
circumstances is always bound to fail, and this for two reasons. In
the first place, it must usually happen that when an organ becomes
useless, natural selection as regards that organ will not only
_cease_, but become _reversed_. For the organ is now absorbing
nutriment, causing weight, occupying space, and so on, _uselessly_.
Hence, even if it be not also a source of actual danger, 'economy
of growth' will determine a reversal of selection against an organ
which is now not merely useless, but deleterious. And this
degenerating influence of the reversal of selection will throughout
be assisted by the cessation of selection, which will now be always
acting round a continuously sinking average. Nevertheless, a point
of balance will eventually be reached in this case, just as it was
in the previous case where the cessation of selection was supposed
to be working alone. For, where the reversal of selection has
reduced the diminishing organ to so minute a size that its presence
is no longer a source of detriment to the organism, the cessation
of selection will carry the reduction a small degree further; and
then the organ will remain as a 'rudiment.' And so it will remain
permanently, unless there be some further reason why the still
remaining force of heredity should be abolished. This further (or
second) reason I found in the consideration that, however enduring
we may suppose the force of heredity to be, we cannot suppose that
it is actually everlasting; and, therefore, that we may reasonably
attribute the eventual disappearance of rudimentary organs to the
eventual failure of heredity itself. In support of this view there
is the fact that rudimentary organs, although very persistent, are
not everlasting. That they should be very persistent is what we
should expect, if the hold which heredity has upon them is great in
proportion to the time during which they were originally useful,
and thus firmly stamped upon the organization by natural selection
causing them to be strongly inherited in the first instance. For
example, we might expect that it would be more difficult finally to
eradicate the rudiment of a wing than the rudiment of a feather;
and accordingly we find it a general rule that long-enduring
rudiments are rudiments of organs distinctive of the higher
taxonomic divisions--i.e. of organs which were longest in building
up, and therefore longest sustained in a state of working
efficiency.
"Thus, upon the whole, my view of the facts of degeneration remains
the same as it was when first published in these columns seventeen
years ago, and may be summarized as follows.
"The cessation of selection when working alone (as it probably does
during the first centuries of its action upon structures or colours
which do not entail any danger to, or perceptible drain upon, the
nutritive resources of the organism) cannot cause degeneration
below, probably, some 10 to 20 per cent. But if from the first the
cessation of selection has been assisted by the _reversal_ of
selection (on account of the degenerating structure having
originally been of a size sufficient to entail a perceptible drain
on the nutritive resources of the organism, having now become a
source of danger, and so forth), the two principles acting together
will continue to reduce the ever-diminishing structure down to the
point at which its presence is no longer a perceptible disadvantage
to the species. When that point is reached, the reversal of
selection will terminate, and the cessation of selection will not
then be able of itself to reduce the organ through more than at
most a very few further percentages of its original size. But,
after this point has been reached, the now total absence of
selection, either for or against the organ, will sooner or later
entail this further and most important consequence, a failure of
heredity as regards the organ. So long as the organ was of use, its
efficiency was constantly _maintained_ by the _presence_ of
selection--which is merely another way of saying that selection was
constantly maintaining the force of heredity as regards that organ.
But as soon as the organ ceased to be of use, selection ceased to
maintain the force of heredity; and thus, sooner or later, that
force began to waver or fade. Now it is this wavering or fading of
the force of heredity, thus originally due to the cessation of
selection, that in turn co-operates with the still continued
cessation of selection in reducing the structure below the level
where its reduction was left by the actual reversal of selection.
So that from that level downwards the cessation of selection, and
the consequent failing of heredity, act and react in their common
work of causing obsolescence. In the case of newly added
characters, the force of heredity will be less than in that of more
anciently added characters; and thus we can understand the long
endurance of 'vestiges' characteristic of the higher taxonomic
divisions, as compared with those characteristic of the lower. But
in all cases, if time enough be allowed under the cessation of
selection, the force of heredity will eventually fall to zero, when
the hitherto obsolescent structure will finally become obsolete. In
cases of newly added and comparatively trivial characters, with
regard to which reversal of selection is not likely to take place
(e.g. slight differences of colour between allied species),
cessation of selection is likely to be very soon assisted by a
failure in the force of heredity; seeing that such newly added
characters will not be so strongly inherited as are the more
ancient characters distinctive of higher taxonomic groups.
"Let us now turn to Weismann's view of degeneration. First of all,
he has omitted to perceive that 'panmixia' alone (if unassisted
either by reversed selection or an inherent diminishing of the
force of heredity) cannot reduce a functionless organ to the
condition of a _rudiment_. Therefore he everywhere represents
panmixia (or the mere _cessation_ of selection) as of itself
sufficient to cause degeneration, say from 100 to 5, instead of
from 100 to 90 or 80, which, for the reasons above given, appeared
(and still appears) to me about the most that this principle can
accomplish, so long as the original force of heredity continues
unimpaired. No doubt we have here what must be regarded as a mere
oversight on the part of Professor Weismann; but the oversight is
rendered remarkable by the fact that he _does_ invoke the aid of
reversed selection _in order to explain the final disappearance of
a rudiment_. Yet it is self-evident that the reversal of selection
must be much more active during the initial than during the final
stages of degeneration, seeing that, _ex hypothesi_, the greater
the degree of reduction which has been attained the less must be
the detriment arising from any useless expenditure of nutrition,
&c.
"And this leads me to a second oversight in Professor Weismann's
statement, which is of more importance than the first. For the
place at which he does invoke the assistance of reversed selection
is exactly the place at which reversed selection must necessarily
have ceased to act. This place, as already explained, is where an
obsolescent organ has become rudimentary, or, as above supposed,
reduced to 5 per cent. of its original size; and the reason why he
invokes the aid of reversed selection at this place is in order to
save his doctrine of 'the stability of germ-plasm.' That the force
of heredity should finally become exhausted if no longer
_maintained_ by the _presence_ of selection, is what Darwin's
theory of perishable gemmules would lead us to expect, while such a
fact would be fatal to Weismann's theory of an imperishable
germ-plasm. Therefore he seeks to explain the eventual failure of
heredity (which is certainly a fact) by supposing that after the
point at which the cessation of selection alone can no longer act
(and which his first oversight has placed some 80 per cent. too
low), the reversal of selection will begin to act directly against
the force of heredity as regards the diminishing organ, until such
direct action of reversed selection will have removed the organ
altogether. Or, in his own words, 'The complete disappearance of a
rudimentary organ can only take place by the operation of natural
selection; this principle will lead to its diminution, inasmuch as
the disappearing structure takes the place and the nutriment of
other useful and important organs.' That is to say, the
rudimentary organ finally disappears, not because the force of
heredity is finally exhausted, but because natural selection has
begun to utilize this force against the continuance of the
organ--always picking out those congenital variations of the organ
which are of smallest size, and thus, by its now _reversed_ action,
_reversing_ the force of heredity as regards the organ.
"Now the oversight here is in not perceiving that the smaller the
disappearing structure becomes, the less hold must 'this principle'
of reversed selection retain upon it. As above observed, during the
earlier stages of reduction (or while co-operating with the
cessation of selection) the reversal of selection will be at its
_maximum_ of efficiency; and, as the process of diminution
continues, a point must eventually be reached at which the reversal
of selection can no longer act. Take the original mass of a now
obsolescent organ in relation to that of the entire organism of
which it then formed a part to be represented by the ratio 1:100.
For the sake of argument we may assume that the mass of the
organism has throughout remained constant, and that by 'mass' in
both cases is meant capacity for absorbing nutriment, causing
weight, occupying space, and so forth. Now, we may further assume
that when the mass of the organ stood to that of its organism in
the ratio of 1:100, natural selection was strongly reversed with
respect to the organ. But when this ratio fell to 1:1000, the
activity of such reversal must have become enormously diminished,
even if it still continued to exercise any influence at all. For we
must remember, on the one hand, that the reversal of selection can
only act as long as the presence of a diminishing organ continues
to be so injurious that variations in its size are matters of life
and death in the struggle for existence; and, on the other hand,
that natural selection in the case of the diminishing organ does
not have reference to the presence and the absence of the organ,
but only to such variations in its mass as any given generation may
supply. Now, the process of reduction does not end even at 1:1000.
It goes on to 1:10,000, and eventually 1:[infinity]. Consequently,
however great our faith in natural selection may be, a point must
eventually come for all of us at which we can no longer believe
that the reduction of an obsolescent organ is due to reversed
selection. And I cannot doubt that if Professor Weismann had
sufficiently considered the matter, he would not have committed
himself to the statement that 'the complete disappearance of a
rudimentary organ can only take place by the operation of natural
selection.'
"According to my view, the complete disappearance of a rudimentary
organ can only take place by the _cessation_ of natural selection,
which permits the eventual exhaustion of heredity, when heredity is
thus simply left to itself. During all the earlier stages of
reduction, the cessation of selection was assisted in its work by
the reversal of selection; but when the rudiment became too small
for such assistance any longer to be supplied, the rudiment
persisted in that greatly reduced condition until the force of
heredity with regard to it was eventually worn out. This appears to
me, as it appeared in 1873, the only reasonable conclusion that can
be drawn from the facts. And it is because this conclusion is fatal
to Professor Weismann's doctrine of the permanent 'stability' of
germ-plasm, while quite in accordance with all theories which
belong to the family of pangenesis, that I deem the facts of
degeneration of great importance as tests between these rival
interpretations of the facts of heredity. It is on this account
that I have occupied so much space with the foregoing discussion;
and I shall be glad to ascertain whether any of the followers of
Professor Weismann are able to controvert these views.
"GEORGE J. ROMANES."
"P.S.--Since the above article was sent in, Professor Weismann has
published in these columns (February 6) his reply to a criticism by
Professor Vines (October 24, 1889). In this reply he appears to
have considerably modified his views on the theory of degeneration;
for while in his Essays he says (as in the passage above quoted)
that 'the complete disappearance of a rudimentary organ can only
take place by the operation of natural selection'--i.e. only by the
_reversal_ of selection,--in his reply to Professor Vines he says,
'I believe that I have proved that organs no longer in use become
rudimentary, and must finally disappear, solely by 'panmixia'; not
through the direct action of disuse, but because natural selection
no longer sustains their standard structure'--i.e. solely by the
_cessation_ of selection. Obviously, there is here a flat
contradiction. If Professor Weismann now believes that a
rudimentary organ 'must finally disappear _solely_' through the
_withdrawal_ of selection, he has abandoned his previous belief
that 'the complete disappearance of a rudimentary organ can _only_
take place by the _operation_ of selection.' And this change of
belief on his part is a matter of the highest importance to his
system of theories as a whole, since it betokens a surrender of his
doctrine of the 'stability' of germ-plasm--or of the virtually
everlasting persistence of the force of heredity, and the
consequent necessity for a reversal of this force itself (by
natural selection placing its premium on _minus_ instead of on
_plus_ variations), in order that a rudimentary organ should
finally disappear. In other words, it now seems he no longer
believes that the force of heredity in one direction (that of
sustaining a rudimentary organ) can only be abolished by the active
influence of natural selection determining this force in the
opposite direction (that of removing a rudimentary organ). It seems
he now believes that the force of heredity, if merely left to
itself by the withdrawal of natural selection altogether, will
sooner or later become exhausted through the mere lapse of time.
This, of course, is my own theory of the matter as originally
published in these columns; but I do not see how it is to be
reconciled with Professor Weismann's doctrine of so high a degree
of stability on the part of germ-plasm, that we must look to the
Protozoa and the Protophyta for the original source of congenital
variations as now exhibited by the Metazoa and Metaphyta.
Nevertheless, and so far as the philosophy of degeneration is
concerned, I shall be very glad if (as it now appears) Professor
Weismann's more recent contemplation has brought his principle of
panmixia into exact coincidence with that of my cessation of
selection."
Before passing on it may here be noted that, to any one who believes in
the inheritance of acquired characters, there is open yet another
hypothetical cause of degeneration, and one to which the final
disappearance of vestigial organs may be attributed. Roux has shown in
his work on _The Struggle for Existence between Parts of an Organism_
that the principle of selection must operate in every constituent
tissue, and as between every constituent cell of which an organism is
composed. Now, if an organ falls into disuse, its constituent cells
become worsted in their struggles with other cells in the organism.
Hence, degeneration of the disused organ may progressively increase,
quite independently of any struggle for existence on the part of the
organism as a whole. Consequently, degeneration may proceed without any
reference to the principle of "economized nutrition"; and, if it does
so, and if the effects of its doing so are transmitted from generation
to generation, the disused organ will finally disappear by means of
Roux's principle.
The long communication above quoted led to a still longer correspondence
in the pages of _Nature_. For Professor Ray Lankester wrote[141] to
impugn the doctrine of panmixia, or cessation of selection, _in toto_,
arguing with much insistence that "cessation of selection must be
supplemented by economy of growth in order to produce the results
attributed to panmixia." In other words, he denied that panmixia alone
can cause degeneration in any degree at all; at most, he said, it can be
but "a condition," or "a state," which occurs when an organ or part
ceases to be useful, and therefore falls under the degenerating
influence of active causes, such as economy of nutrition. Or, in yet
other words, he refused to recognize that any degenerative process can
be due to natural selection as merely withdrawn: only when, besides
being _withdrawn_, natural selection is _reversed_, did he regard a
degenerative process as possible. As a result of the correspondence,
however, he eventually[142] agreed that, if the "birth-mean" of an
organ, in respect either of size or complexity of structure, be lower
than the "selection-mean" while the organ is useful (a fact which he
does not dispute); then, if the organ ceases to be useful, it will
degenerate by the withdrawal of selection alone. Which, of course, is
merely a re-statement of the doctrine of panmixia, or cessation of
selection, in somewhat varied terminology--provided that the birth-mean
be taken over a number of generations, or not only over a few following
the selection-mean of the structure while still in its highest state of
efficiency. For the sake of brevity I will hereafter speak of these "few
following" generations by the term of "first generations."
[141] _Nature_, vol. xli. p. 486.
[142] _Ibid._ vol. xlii. p. 52.
It remains to consider the views of Professor Lloyd Morgan upon the
subject. In my opinion he is the shrewdest, as well as the most logical
critic that we have in the field of Darwinian speculation; therefore, if
possible, I should like to arrive at a full agreement with him upon this
matter. His latest utterance with regard to it is as follows:--
"To account for the diminution of organs or structures no longer of
use, apart from any inherited effects of disuse, Mr. Romanes has
invoked the Cessation of Selection; and Mr. Francis Galton has, in
another connexion, summarized the effects of this cessation of
selection in the convenient phrase 'Regression to Mediocrity.' This
is the Panmixia of Professor Weismann and his followers; but the
phrase regression to mediocrity through the cessation of selection
appears to me preferable. It is clear that so long as any organ or
structure is subject to natural selection through elimination, it
is, if not actually undergoing improvement, kept at a high standard
of efficiency through the elimination of all those individuals in
which the organ in question falls below the required standard. But
if, from change in the environment or any other cause, the
character in question ceases to be subject to selection,
elimination no longer takes place, and the high standard will no
longer be maintained. There will be reversion to mediocrity. The
probable amount of this reversion is at present a matter under
discussion[143]."
[143] _Presidential Address to the Bristol Naturalists' Society_,
1891.
So far, then, Professor Lloyd Morgan is in complete agreement with
previous writers upon the subject. He does not doubt that the cessation
of selection must always be a cause of degeneration: the only question
is as to the _potency_ of this cause, or the _amount_ of degeneration
which it is capable of effecting.
Taking, first, the case of bulk or size of an organ, as distinguished
from its organization or complexity, we have seen that Weismann
represents the cessation of selection--even if working quite alone, or
without any assistance from the reversal of selection--to be capable of
reducing a fully developed organ to the state of a rudiment, or even, if
we take his most recent view, of abolishing the organ _in toto_.
Professor Lloyd Morgan, on the other hand, does not think that the
cessation of selection alone can cause reduction further than the level
of "mediocrity" in the first generations--or, which is much the same
thing, further than the difference between the "birth-mean" and the
"selection-mean" of the first generations. This amount of reduction he
puts at 5 per cent., as "a very liberal estimate."
Here, then, we have three estimates of the amount of degeneration which
can be produced by panmixia alone, where mere size or bulk of an organ
is concerned--say, 3 to 5 per cent., 10 to 20 per cent., and 95 per
cent. to 0. At first sight, these differences appear simply ludicrous;
but on seeking for the reasons of them, we find that they are due to
different views touching the manner in which panmixia operates. The
oversights which have led to Weismann's extremely high estimate have
already been stated. The reason of the difference between the extremely
low estimate of Professor Lloyd Morgan, as compared with my own
intermediate one, is, that he supposes the power of panmixia to become
exhausted as soon as the level of mediocrity of the first generations
has become the general level in succeeding generations. In my view,
however, the level of mediocrity is itself a sinking level in
successive generations, with the result that there is no reason why the
reducing power of panmixia should ever become exhausted, save that the
more reduction it effects the greater is the force of heredity which
remains to be overcome, as previously explained. Thus the only question
between Professor Lloyd Morgan and myself is--Does the level of
mediocrity fall in successive generations under the cessation of
selection, or does it remain permanently where it used to be under the
presence of selection? Does the "birth-mean" remain constant throughout
any number of generations, notwithstanding that the sustaining influence
of selection has been withdrawn; or does it progressively sink as a
consequence of such withdrawal?
In order to answer this question we had better begin by considering now
the case of organization of structure, as distinguished from mere size
of structure. Take any case where a complex organ--such as a compound
eye--has been slowly elaborated by natural selection, and is it not
self-evident that, when natural selection is withdrawn, the complex
structure will deteriorate? In other words, the level of mediocrity, say
in the hundred thousandth generation after the sustaining influence of
natural selection has been withdrawn, will not be so high as it was in
the first generations. For, by hypothesis, there is now no longer any
elimination of unfavourable variations, which may therefore perpetuate
themselves as regards any of the parts of this highly complex mechanism;
so that it is only a matter of time when the mechanism must become
disintegrated. I can scarcely suppose that any one who considers the
subject will question this statement, and therefore I will not say
anything that might be said in the way of substantiating it. But, if the
statement be assented to, it follows that there is no need to look for
any cause of deterioration, further than the withdrawal of selection--or
cessation of the principle which (as we are supposing) had hitherto
been the sole means of maintaining efficient harmony among all the
independently variable parts of the highly complex structure.
Now, I hold that the same thing is true, though in a lesser degree, as
regards degeneration of size. That there is no difference _in kind_
between the two cases, Professor Lloyd Morgan implicitly allows; for
what he says is--
"In any long-established character, such as wing-power in birds,
brain-development, the eyes of crustacea, &c., no shortcomer in
these respects would have been permitted by natural selection to
transmit his shortcomings for hundreds of generations. All tendency
to such shortcomings would, one would suppose, have been bred out
of the race. If after this long process of selection there still
remains a strong tendency to deterioration, this tendency demands
an explanation[144]."
[144] _Presidential Address to the Bristol Naturalists' Society_,
1891.
Here, then, deterioration as to size of structure (wings of birds), and
deterioration as to complexity of structure (brain and eyes) are
expressly put upon the same footing. Therefore, if in the latter case
the "tendency to deterioration" does not "demand an explanation," beyond
the fact that the hitherto maintaining influence has been withdrawn,
neither is any such further explanation demanded in the former case.
Which is exactly my own view of the matter. It is also Mr. Galton's
view. For although, in the passage formerly quoted, Professor Lloyd
Morgan appears to think that by the phrase "Regression to Mediocrity"
Mr. Galton means to indicate that panmixia can cause degeneration only
as far as the mediocrity level of the first generations, this, in point
of fact, is not what Galton means, nor is it what he says. The phrase in
question occurs "in another connexion," and, indeed, in a different
publication. But where he expressly alludes to the cessation of
selection, this is what he says. The italics are mine.
"A special cause may be assigned for the effects of use in causing
hereditary _atrophy_ of disused parts. It has already been shown
that all exceptionally developed organs tend to deteriorate:
consequently, those that are not _protected_ by selection will
_dwindle_. The level of muscular efficiency in the wing of a
strongly flying bird [curiously enough, the same case that is
chosen by Professor Lloyd Morgan to illustrate his opposite view],
is like the level of water in the leaky vessel of a Danaid, only
secured to the race by _constant effort_, so to speak. _Let the
effort be relaxed ever so little, and the level immediately
falls[145]._"
[145] _A Theory of Heredity_, Journal of Anthropological Institute,
1875. Vol. v. p. 345.
I take it, then, that the burden of proof lies with Professor Lloyd
Morgan to show why the withdrawal of selection is _not_ sufficient to
account for degeneration any further than the mediocrity-level in the
former presence of selection. Why does "the strong tendency[146] to
deterioration demand an explanation," further than the fact that when
all variations below the average in every generation are allowed to
survive, they must gradually lower the average itself through a series
of generations? To answer that any such tendency "would have been bred
out of the race" by the previous action of selection, is to suppose that
the function of selection is at an end when once it has built up a
structure to the highest point of working efficiency,--that the presence
of selection is no longer required to _maintain_ the structure at that
point. But it is enough to ask in reply--Why, under the cessation of
selection, does _complexity_ of structure degenerate so much more
rapidly than _size_ of structure? Why is it, for instance, that "the
eyes of crustacea" in dark caves have entirely disappeared, while their
foot-stalks (when originally present) still remain? Can it be maintained
that "for hundreds of generations" natural selection was more intent on
developing the foot-stalks than the eyes which were mounted upon
them--so that while the latter were left by selection with "a strong
tendency to deterioration," the former have had this tendency "bred out
in the race"[147]?
[146] No one has supposed that the tendency need be "strong": it has
only to be persistent.
[147] Of course it must be observed that degeneration of complexity
involves also degeneration of size, so that a more correct
statement of the case would be--Why, under the cessation of
selection, does an organ of extreme complexity degenerate much
more rapidly than one of much less complexity? For example,
under domestication the brains of rabbits and ducks appear to
have been reduced in some cases by as much as 50 per cent.
(Darwin, and Sir J. Crichton Browne.) But if it is possible to
attribute this effect--or part of it--to an artificial
selection of stupid animals, I give in the text an example
occurring under nature. Many other cases, however, might be
given to show the general rule, that under cessation of
selection complexity of structure degenerates more
rapidly--and also more thoroughly--than size of it. This, of
course, is what Mr. Galton and I should expect, seeing that
the more complex a structure the greater are the number of
points for deterioration to invade when the structure is no
longer "protected by selection." (On the other hand, of
course, this fact is opposed to the view that degeneration of
useless structures below the "birth-mean" of the first
generations, is exclusively due to the reversal of selection;
for economy of growth, deleterious effect of weight, and so
forth, ought to affect size of structure _much more_ than
complexity of it.) But I choose the above case, partly because
Professor Lloyd Morgan has himself alluded to "the eyes of
crustacea," and partly because Professor Ray Lankester has
maintained that the loss of these eyes in dark caves is due to
the reversal of selection, as distinguished from the cessation
of it. In view of the above parenthesis it will be seen that
the point is not of much importance in the present connexion;
but it appears to me that cessation of selection must here
have had at least the larger share in the process of atrophy.
For while the economy of nutrition ought to have removed the
relatively large _foot-stalks_ as rapidly as the _eyes_, I
cannot see that there is any advantage, other than the economy
of nutrition, to be gained by the rapid loss of hard-coated
_eyes_, even though they have ceased to be of use.
To sum up. There is now no question in any quarter touching the fact
that panmixia, or the cessation of selection, is a true cause of
degeneration. The only question is as to the amount of degeneration
which it is able to effect when not assisted by the reversal of
selection, or any other cause of degeneration. Moreover, even with
regard to this question of amount, there is no doubt on any side that
panmixia alone causes degeneration _more rapidly_ where it has to do
with complexity of organization, than it does where it is concerned with
a mere reduction of mass.
The question as to the amount of degeneration that is caused by the
cessation of selection alone is without any practical importance where
species in a state of nature are concerned, because here the cessation
of selection is probably always associated more or less with the
reversal of it; and it is as impossible as it is immaterial to determine
the relative shares which these two co-operating principles take in
bringing about the observed results. But where organisms in a state of
domestication are concerned, the importance of the question before us is
very great. For if the cessation of selection alone is capable of
reducing an organ through 10 or 12 per cent. of its original size,
nearly all the direct evidence on which Darwin relied in favour of
use-inheritance is destroyed. On the other hand, if reduction through 5
per cent. be deemed a "very liberal estimate" of what this principle can
accomplish, the whole body of Darwin's direct evidence remains as he
left it. I have now given my reasons for rejecting this lower estimate
on the one band, and what seems to me the extravagant estimate of
Weismann on the other. But my own intermediate estimate is enough to
destroy the apparent proof of use-inheritance that was given by Darwin.
Therefore it remains for those who deny Lamarckian principles, either to
accept some such estimate, or else to acknowledge the incompatibility of
any lower one with the opinion that there is no evidence in favour of
these principles.
APPENDIX II.
ON CHARACTERS AS ADAPTIVE AND SPECIFIC.
It is the object of this Appendix to state, more fully than in the text,
the opinions with regard to this subject which have been published by
the two highest authorities on the theory of natural selection--Darwin
and Professor Huxley. I will take first the opinion of Professor Huxley,
quoted _in extenso_, and then consider it somewhat more carefully than
seemed necessary in the text.
As far as I am aware, the only occasion on which Professor Huxley has
alluded to the subject in question, is in his obituary notice of Darwin
in the _Proceedings of the Royal Society_, Vol. XLIV, No. 269, p. xviii.
The allusion is to my paper on _Physiological Selection_, in the
_Journal of the Linnaean Society_, Zool. Vol. XIX, pp. 337-411. But it
will be observed that the criticism has no reference to the theory which
it is the object of that paper to set forth. It refers only to my
definition of the theory of natural selection as primarily a theory of
the origin, or cumulative development, of adaptations. This criticism,
together with my answer thereto at the time, is conveyed in the
following words.
"Every variety which is selected into a species is favoured and
preserved in consequence of being, in some one or more respects,
better adapted to its surroundings than its rivals. In other words,
every species which exists, exists in virtue of adaptation, and
whatever accounts for that adaptation accounts for the existence of
the species. To say that Darwin has put forward a theory of the
adaptation of species, but not of their origin, is therefore to
misunderstand the first principles of the theory. For, as has been
pointed out, it is a necessary consequence of the theory of
selection that every species must have some one or more structural
or functional peculiarities, in virtue of the advantage conferred
by which it has fought through the crowd of its competitors, and
achieved a certain duration. In this sense, it is true that every
species has been 'originated' by selection."
Now, in the first place, I have nowhere said that "Darwin has put
forward a theory of the adaptation of species, but not of their
origin." I said, and continue to say, that he has put forward a
theory of _adaptations in general_, and that where such adaptations
appertain to species only (i.e. are peculiar to particular
species), the theory becomes "_also_ a theory of the origin of the
species which present them." The only possible misunderstanding,
therefore, which can here be alleged against me is, that I fail to
perceive it as a "necessary consequence of the theory of selection
that _every_ species _must_ have some one or more structural or
functional _peculiarities_" of an adaptive or utilitarian kind.
Now, if this is a misunderstanding, I must confess to not having
had it removed by Mr. Huxley's exposition.
The whole criticism is tersely conveyed in the form of two sequent
propositions--namely, "Every species which exists, exists in virtue
of adaptation; and whatever accounts for that adaptation accounts
for the existence of the species." My answer is likewise two-fold.
First, I do not accept the premiss; and next, even if I did, I can
show that the resulting conclusion would not overturn my
definition. Let us consider these two points separately, beginning
with the latter, as the one which may be most briefly disposed of.
I. Provisionally conceding that "every species which exists, exists
in virtue of adaptation," I maintain that my definition of the
theory of natural selection still holds good. For even on the basis
of this concession, or on the ground of this assumption, the theory
of natural selection is not shown to be "_primarily_" a theory of
the origin of species. It follows, indeed, from the assumption--is,
in fact, part and parcel of the assumption--that all species have
been originated by natural selection; but why? _Only because
natural selection has originated those particular adaptive features
in virtue of which (by the hypothesis) species exist as species._
It is only in virtue of having created these features that natural
selection has created the species presenting them--just as it has
created genera, families, orders, &c., in virtue of _other_
adaptive features extending through progressively wider areas of
taxonomic division. Everywhere and equally this principle has been
"primarily" engaged in the evolution of adaptations, and if one
result of its work has been that of enabling the systematist to
trace lines of genetic descent under his divisions of species,
genera, and the rest, such a result is but "secondary" or
"incidental."
In short, it is "_primarily_" a theory of adaptations _wherever
these occur_, and only becomes "_also_" or "_incidentally_" a
theory of species in cases where adaptations happen to be
restricted in their occurrence to organic types of a certain order
of taxonomic division.
II. Hitherto, for the sake of argument, I have conceded that, in
the words of my critic, "it is a necessary consequence of the
theory of selection that every species must have some one or more
structural or functional peculiarities" of an adaptive kind. But
now I will endeavour to show that this statement does not "follow
as a necessary consequence" from "the theory of selection."
Most obviously "it follows" from the theory of selection that
"every variety which is selected into a species is favoured and
preserved in consequence of being, in some one or more respects,
better adapted to its surroundings than its rivals." This, in fact,
is no more than a re-statement of the theory itself. But it does
_not_ follow that "every species which exists, exists in virtue of
adaptation" _peculiar to that species_; i.e. that every species
which exists, exists _in virtue of having been "selected_." This
may or may not be true as a matter of fact: as a matter of logic,
the inference is not deducible from the selection theory. Every
variety which is "_selected into_" a species must, indeed, present
some such peculiar advantage; but this is by no means equivalent to
saying, "in other words," that every variety which _becomes_ a
species must do so. For the latter statement imports a completely
new assumption--namely, that every variety which _becomes_ a
species must do so because it has been "_selected into_" a species.
In short, what we are here told is, that if we believe the
selection principle to have given origin to some species, we must
further believe, "as a necessary consequence," that it has given
origin to all species.
The above reply, which is here quoted _verbatim_ from _Nature_, Vol. 38,
p. 616-18, proceeded to show that it does not belong to "the first
principles of the theory of natural selection" to deny that no other
cause than natural selection can possibly be concerned in the origin of
species; and facts were given to prove that such unquestionably has been
the case as regards the origin of "local" or "permanent" _varieties_.
Yet such varieties are what Darwin correctly terms "incipient" species,
or species in process of taking _origin_. Therefore, if Professor
Huxley's criticism is to stand at all, we must accept it "as a necessary
consequence of the theory of selection," that every such _variety_
"which exists, exists in virtue of adaptation"--a statement which is
_proved_ to be untrue by the particular cases forthwith cited. But as
this point has been dealt with much more fully in the text of the
present treatise, I shall sum up the main points in a few words.