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Vernon L. (Vernon Lyman) Kellogg.

Darwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming online

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Online LibraryVernon L. (Vernon Lyman) KelloggDarwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming → online text (page 32 of 38)
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er the struggle for existence,
the more energetically selection
works, and therewith the quick-



ACCORDING TO THE THEORY OF
HETEROGENESIS.

1. To all organisms there be-
longs a capacity for variation,
which is a fundamental inner
peculiarity independent of outer
conditions, and which remains
usually in latent condition, re-
tained by heredity, but which
now and then finds its expres-
sion in sudden changes.

2. These sudden changes can,
under favourable conditions, be
the beginnings of persistent
races. These new characteris-
tics, having appeared independ-
ently of outer conditions, are
sometimes useful to the organ-
ism, but they may also stand in
no harmony with outer condi-
tions.



3. All once-formed species re-
main unchanged, although new
forms occasionally split off from
them by heterogenesis. Such
newly-arisen forms have, as the
result of a disturbed heredity, a
deranged constitution, which re-
veals itself in a lessened fertility
and often in a generally weak-
ened condition of the organism.
The new forms, becoming con-
stant races, gradually recover
their constitution.

4. The origin of new forms
can, however, occur only under
favourable conditions of exist-
ence for the species, and the
more favourable these condi-
tions, that is, the less severe
the struggle for existence, the



OTHER THEORIES OF SPECIES-FORMING. 335



er the development of new
forms.



5. The chief requisite for evo-
lution is, therefore, the struggle
for existence and the selection
which, results from it.



6. If there were no struggle
for existence, no selection, no
survival of the strongest, there
would be no evolution and no
specialisation, for adapted spe-
cies would have no advantage
over unadapted ones, and as a
result of crossing with the lat-
ter, they would sacrifice their
useful characteristics.

7. The so-called advance in
nature or the perfecting of or-
ganisms, is nothing else than a
more complex, more complete
adaptation to outer conditions,
and it is reached in a purely
mechanical way through selec-
tion and the accumulation of
characteristics useful under the
existent outer conditions.



more energetically can evolution
go on. New forms do not arise
under hard external conditions,
or if any do, they go quickly to
ground.

5. The struggle for existence,
and the selection that goes hand
in hand with it, constitute a fac-
tor which limits new forms and
hinders further variation and is,
therefore, in no way favourable
to the origin of new forms. It
is a factor inimical to evolution.

6. If there were no struggle
for existence, there would be no
killing out of newly arising or al-
ready arisen forms. The world
of organisms could then grow to
a mighty tree, whose branches
could all persist in blossoming
condition, and the most aberrant,
now isolated, species would be
connected with all others through
intermediate forms.

7. The adaptation which
comes to exist through the
struggle for existence is not at
all identical with an advance, for
higher, more specialised (voll-
kommenerc} forms are by no
means always better adapted to
outer conditions than the lower
ones. One cannot explain the
evolution of organisms in a
purely mechanical way. In or-
der to explain the origin of
higher forms out of lower it is
necessary to admit a special
tendency, in organisms, for ad-
vance, which is nearly related
to, or identical with the tend-
ency to vary, and which com-
pels organisms toward perfect-
ness as far as external conditions
allow.

The theory of heterogenesis as formulated by Korschinsky
(and also as held by de Vries, as we shall see) is not neces-



336 DARWINISM TO-DAY.

sarily a theory of sudden large changes or variations, al-
though it is of sudden and fixed ones. It is not based on
any belief that sports or large variations are any more
numerous, nor of any more worth as the beginnings of new
species, than now generally recognised, but it assumes
sudden radical changes in the organism which, if not visibly
large as regards obvious quantitative conditions, are large or
at least comprehensive as regards qualitative conditions.
The mutation or variation assumed by the theory of hetero-
genesis affects many organs and parts, structurally and
physiologically ; it produces a radical change throughout the
organism. And this change is the result of an influence
wholly intrinsic, inherent, and has no reference to external
conditions, except in that the stimulus for it may come partly
or chiefly from specially favourable conditions of nutrition.
This change is at once definitive and fixed : it is transmitted
unimpaired to the offspring of the organism showing the
mutation, only the capacity for the production of offspring,
4. e., the reproductive fertility, is often weakened.

Korschinsky's theory and declarations are not based on
any very large amount of personal experimentation and
observation at least his references to new facts are few and
meagre. He gives a short list of old and more or less
familiar together with a few new examples of heterogenesis
but he does not lend the theory of heterogenesis very much
in the way of authority, except in so far as the evidently
positive and clear conviction on the part of a biologist of
experience and reputable standing of the necessity and truth
of such a theory is authority. Korschinsky's conviction is
probably based on much observation and experience besides
that which he definitely catalogued, but what is needed to
carry conviction to others is direct reference to proved, and
where possible verifiable, facts of observation and experi-
ment.

The supplying of this demand, to a degree which will



OTHER THEORIES OF SPECIES-FORMING. 337

appear to various people insufficient or sufficient according

to their respective ideas of what is needed in

De Vries and the way of fact material for the satisfactory

the mutations .... ,. , , . ,

theory. founding of a theory, it is the special vir-

tue of de Vries to have attempted on behalf
of heterogenesis.

De ^ries 12 introduces his now classic two-volume pres-
entation of his views on evolution and species-forming
("Die Mutationstheorie," 1901-1903) with the following
paragraph :

"Als Mutationstheorie bezeichne ich den Satz, dass die
Eigenschaften der Organismen aus scharf von einander
unterschiedenen Einheiten aufgebaut sind. Diese Einheiten
konnen zu Gruppen verbunden sein, und in verwandten
Arten kehren dieselben Einheiten und Gruppen wieder.
tibergange, wie sie uns die ausseren Formen der Pflanzen
und Thiere so zahlreich darbieten, giebt es aber zwischen
diesen Einheiten ebensowenig, wie zwischen den Molekiilen
der Chemie." And again in the first paragraph of the
preface to his book "Species and Varieties" IJ (an edited
transcription of his American lectures on species-forming,
delivered in California in 1904) he says: ". . .{but the
way in which one species originates from another has not
been adequately explained. The current belief assumes that
species are slowly changed into new types. In contradic-
tion to this conception the theory of mutation assumes that
new species and varieties are produced from existing forms
by sudden leapsi The parent-type itself remains unchanged
throughout this process, and may repeatedly give birth to
new forms. These may arise simultaneously and in groups,
or separately at more or less widely distributed periods."

Obviously there is no ambiguity here as to the relation
of species-forming by mutation to species-forming by
gradual modification through selection or fluctuating varia-
tions. In the words of de Vries : "Species have not arisen



338 DARWINISM TO-DAY.

through gradual selection continued for hundreds or thou-
sands of years, but by jumps (stufenwcise) through sudden,
though small, transformations. In contrast with variations
which are changes in a linear direction the transformations
to be called mutations constitute divergence in new directions.
They take place, so far as experience goes, without definite
direction." ' ' And even if transition forms exist between
the species produced by mutations, they are no evidence
against the mutations, "for," says de Vries, "the transitions
do not appear before the new species, at most only simul-
taneously with this, and generally only after this is already
in existence. The transitions are therefore no intermediates
or preparations for the appearance of the new forms. The
origin takes place, not through them, but wholly independ-
ently of them." 15

Too often de Vries's theory is said not to be alternative
with Darwin's, but auxiliary to it. As regards the forma-
tion of new species, the two theories are directly
De Vries's in opposition. But as regards the general
opposition to course of organic evolution (which is another
Darwin's as con- matter) the mutations theory is not in contra-

cerns species- . .

forming. diction to the theory of descent through

selection, De Vries himself says: "Notwith-
standing all these apparently unsurmountable difficulties,
Darwin discovered the great principle which rules the evolu-
tion of organisms. It is the principle of naturaLselection.
It is the sifting out of all organisms of minor worth through
the struggle for life. It is only a sieve, and not a force of
nature, no direct cause of improvement, as many of Dar-
win's adversaries, and unfortunately many of his followers
also, have so often asserted. It is only a sieve, which de-
cides which is to live, and what is to die. But evolutionary
lines are of great length, and the evolution of a flower or
of an insectivorous plant is a way with many side-paths. It
is the sieve that keeps evolution on the main line, killing-



OTHER THEORIES OF SPECIES-FORMING. 339

all or nearly all that try to go in other directions. By this
means natural selection is the one directing cause of the
broad lines of evolution." *

While de Vries admits that recorded mutations are few ;
"mutations under observation are as yet very rare; enough
to indicate the possible and most probable ways but no
more 1 ;" 1T yet he strongly maintains that there is no scientific
proof of the origin of species in any other way than by
mutation and that there is such proof of their actual muta-
tional origin. He says : "I intend to give a review of the
facts obtained from plants which go to prove the assertion
that species and varieties have originated by mutation and
are, at present, not known to originate in another way."

But in any consideration of de Vries's work and theories,
one must have clearly in mind the distinctive meaning
which de Vries attaches to the word species. However
little biologists agree on any absolute definition of species,
the term nevertheless is consistently used to refer to differ-
entiated organic types between any two of which there is
considerable obvious describable difference, either quali-
tative or quantitative. If two types of such obvious differ-
ence in one or several characteristics (usually external or
at least externally noticeable differences are the ones used)
are connected by a series of connecting gradatory forms
existing either in the same territory or in other regions, the
two forms are not referred to as distinct species but as
varieties ; at least the form at one end of the series is called
a variety of the form at the other end. But de Vries's
species and varieties are of different stuff. Specific dis-
tinctions with him are based on differences in aggregation
of the elementary units, the Einheiten, that go to compose
the specific types. "Species is a word," says de Vries,
"which always has had a double meaning. One of them is
the systematic species, which is the unit of our system.
But these units are not at all indivisible. Long ago Lin-



340 DARWINISM TO-DAY.

naeus knew them to be compound ideas in a great number
of instances, and increasing knowledge has shown that the
same rule prevails in other instances. To-day the vast ma-
jority of the old systematic species are known to consist of
minor units. These minor entities are called varieties in sys-
tematic works. However, there are many objections to this
usage. First, the term variety is applied in horticulture and
agriculture to things so widely divergent as to convey no
clear idea at all. Secondly, the subdivisions of species are
by no means all of the same nature, and the systematic
varieties include units the real value of which is widely
different in different cases. Some of these varieties are in
reality as good as species, and have been 'elevated,' as it is
called, by some writers, to this rank. This conception of the
elementary species would be quite justifiable, and would at
once get rid of all difficulties, were it not for one practical
obstacle. The number of the species in all genera would be
doubled and tripled, and as these numbers are already
cumbersome in many cases, the distinction of the native
species of any given country would lose most of its charm
and interest.

"In order to meet this difficulty we must recognise two
sorts of species. The systematic species are the practical
units of the systematists and florists, and all friends of wild
nature should do their utmost to preserve them as Linnaeus
has proposed them. These units, however, are not really
existing entities; they have as little claim to be regarded
as such as the genera and families have. The real units
are the elementary species; their limits often apparently
overlap and can only in rare cases be determined on the
sole ground of field-observations. Pedigree-culture is the
method required and any form which remains constant and
distinct from its allies in the garden is to be considered as
an elementary species." "

With regard to varieties de Vries has the following to



OTHER THEORIES OF SPECIES-FORMING. 341

say : "Linnaeus himself knew that in some cases all sub-
divisions of a species are of equal rank, together constituting
the group called species. No one of them outranks the
others; it is not a species with varieties, but a group con-
sisting only of varieties. A closer inquiry into the cases
treated in this manner by the great master of systematic
science shows that here his varieties were exactly what we
now call 'elementary species.

"In other cases the varieties are of a derivative nature.
The species constitutes a type that is pure in a race which
ordinarily is still growing somewhere, though in some cases
it may have died out. From this type the varieties are
derived, and the way of this derivation is usually quite
manifest to the botanist. It is ordinarily by the disappear-
ance of some superficial character that a variety is dis-
tinguished from its species, as by the lack of colour in the
flowers, of hairs on stems and foliage, of the spines and
thorns, etc. Such varieties are, strictly speaking, not to be
treated in the same way as elementary species, though they
often are. We shall designate them by the term of 'retro-
grade varieties,' which clearly indicates the nature of their
relationship to the species from which they are assumed to
have sprung. In order to lay more stress on the contrast
between elementary species and retrograde varieties, it
should be stated at once, that the first are considered to
have originated from their parent-form in a progressive
way. They have succeeded in attaining something quite
new for themselves, while retrograde varieties have only
thrown off some peculiarity, previously acquired by their
ancestors." '

With regard to the facts and general evidence 20 on which
de Vries bases his beliefs and theory a few

Ine facts at

basis of de words, too few, I regret, must suffice. Like
Vries's theory. ) arw j nj ^e y r i es on i y came to the full pub-
lication of his theory after many years of assiduous obser-



342 DARWINISM TO-DAY.

vation, of persistent compilation of other men's observing,
and careful weighing and consideration of the data in
hand. In de Vries's case too there was added a large
amount of experimental testing of his conclusions. This
experimental study of the species-forming problem de
Vries and his followers rather seem to claim as a distinct-
ively new part of the basis for the mutations theory, but as
a matter of fact Darwin himself, in much less degree per-
haps, and in somewhat different manner, appealed to experi-
ment to test many of his conclusions. The actual forming
of new species by selection could not be experimentally
tested or proven by Darwin. Whether biologists are ready
to accept de Vries's pedigree-culture work and results as
of the same nature of rigid experimental test and proof as
there exists in experimentation in chemistry and static
physics (for that is the claim for the new "experimental
method" in biology) remains, perhaps, a moot point. De
Vries's general statement of the character and the amount
of the evidence on which he rests his belief in the formation
of species by mutation is contained in the following para-
graphs from his book "Species and Varieties" (p. 22).

"Mutations are occurring from time to time in the wild
state as well as in horticulture and agriculture. A selec-
tion of the most interesting instances will be given later.
But in all such cases the experimental proof is wanting.
The observations, as a rule, only began when the mutation
made its appearance. A more or less vague remembrance
about the previous state of the plants in question might be
available, though even this is generally absent. But on
doubtful points concerning possible crosses or possible intro-
duction of foreign strains, mere recollection is insufficient.
The fact of the mutation may be very probable, but the full
proof is, of course, wanting. Such is the case with the
mutative origin of Xanthium commune Wootoni from New
Mexico and of (Enothera biennis cruciata from Holland.



OTHER THEORIES OF SPECIES-FORMING. 343

The same doubt exists as to the origin of the Capsella
Heegeri of Solms-Laubach, and of the oldest recorded muta-
tion, that of Chelidonium laciniatum in Heidelberg about
1600."

Next, after introducing the necessity of experimental
proof and explaining how one must go to work to acquire
such 'proof he refers to his own well-known work with
Lamarck's evening primrose as follows (pp. 26-29) :

"Complying with these conditions, the origin of species

may be seen as easily as any other phenomenon. It is only

necessary to have a plant in a mutable condi-

The work with tion. Not all species are in such a state at

Lamarck's even- , , . , , ,

ing primrose* present, and therefore I have begun by ascer-
taining which were stable and which were not.
These attempts, of course, had to be made in the experi-
mental garden, and large quantities of seed had to be pro-
cured and sown. Cultivated plants, of course, had only a
small chance to exhibit new qualities, as they have been so
strictly controlled during so many years. Moreover their
purity of origin is in many cases doubtful. Among the wild
plants only those could be expected to reward the investi-
gator which were of easy cultivation. For this reason I
have limited myself to the trial of wild plants of Holland,
and have had the good fortune to find among them at least
one species in a state of mutability. It was not really a
native plant, but one probably introduced from America
or at least belonging to an American genus. It was the
great evening-primrose or the primrose of Lamarck. A
strain of this beautiful species is growing on an abandoned
field in the vicinity of Hilversum, at a short distance from
Amsterdam. Here it has escaped from a park, and multi-
plied. In doing so it has produced, and is still producing,
quite a number of new types, some of which may be con-
sidered as retrograde varieties, while others evidently are
of the nature of progressive elementary species.



344 DARWINISM TO-DAY.

"This interesting plant has afforded me the means of ob-
serving directly how new species originate, and of studying
the laws of these changes. My researches have followed a
double line of inquiry. On one side, I have limited myself
to direct field observations, and to trials of seed, collected
from the wild plants in their native locality. Obviously the
mutations are decided within the seed, and the culture of
young plants from them had no other aim than that of
ascertaining what had occurred in the field. But then the
many chances of destruction that threaten young plants in a
wild state could be avoided in the garden, where environ-
mental factors can be controlled.

"My second line of inquiry was an experimental repetition
of the phenomena which were only partly discerned at the
native locality. It was not my aim to intrude into the
process, nor to try to bring out new features. My only ob-
ject was to submit to the precepts just given concerning
pure treatment, individual seed-gathering, exclusion of
crosses, and accurate recording of all the facts. The result
has been a pedigree which now permits of stating the rela-
tion between all the descendants of my original introduced
plant. This pedigree at once exhibits the laws followed by
the mutating species. The main fact is, that it does not
change itself gradually, but remains unaffected during all
succeeding generations. It only throws off new forms,
which are sharply contrasted with the parent, and which
are from the very beginning as perfect and as constant, as
narrowly defined, and as pure of type as might be expected
of any species.

"These new species are not produced once or in single
individuals, but yearly and in large numbers. The whole
phenomenon conveys the idea of a close group of mutations,
all belonging to one single condition of mutability. Of
course this mutable state must have had a beginning, as it
must sometime come to an end. It is to be considered as a



OTHER THEORIES OF SPECIES-FORMING. 345

period within the life-time of the species, and probably it is
only a small part of it."

The following paragraphs and diagram quoted from
Morgan 21 give an admirably concise statement of the actual
details of the primrose mutations observed by de Vries.

"We may now proceed to examine the evidence from
which* de Vries has been led to the general conclusions given
in the preceding pages. De Vries found at
aoooStof de Hilversum, near Amsterdam, a locality where
Vries's experi- a number of plants of the evening primrose,
(Enothera lamarckiana, grow in large numbers.
This plant is an American form [native to the Southern
United States] that has been imported into Europe. It
often escapes from cultivation, as is the case at Hilversum,
where for ten years it has been growing wild. Its rapid
increase in numbers in the course of a few years may be one
of the causes that have led to the appearance of a mutation
period. The escaped plants showed fluctuating variations
in nearly all of their organs. They also had produced a
number of abnormal forms. Some of the plants came to
maturity in one year, others in two, or in rare cases in
three, years.

"A year after the first finding of these plants de Vries
observed two well-characterised forms, which he at once
recognised as new elementary species. One of these was
O. brevistylis, which occurred only as female plants. The
other new species was a smooth-leafed form with a more
beautiful foliage than 0. lamarckiana. This is O. lavtfolia.
It was found that both of these new forms bred true from
self-fertilised seeds. At first only a few specimens were
found, each form in a particular part of the field, which
looks as though each might have come from the seeds of a
single plant.

"These two new forms, as well as the common O. la-
marckiana, were collected, and from these plants there have



346



DARWINISM TO-DAY.



arisen the three groups or families of elementary species that
de Vries has studied. In his garden other new forms also
arose from those that had been brought under cultivation.
The largest group and the most important one is that from
the original 0. lamarckiana form. The accompanying table

CENOTHERA LAMARCKIANA.

ELEMENTARY SPECIES.



GENERATION.


till

i i 1 11 si


q

3 1


3 < o * j z


3 3


VIII.


8 Gener.
1899
annual
7 Gener.
1898
annual
6 Gener.
1897
annual
5 Gener.
1896
annual
4 Gener.
1895
annual
3 Gener.
1890-91
biennial
2 Gener.
1888-89
biennial
i Gener.
1886-87
biennial


5IO I,7OO 21


i


VII....


9 o 3,000 ii


5 i


VI


II 29 3 i, 800 9


v


25 135 20 8,000 49


142 6


IV


i 15 176 8 14,000 60


73 i



Online LibraryVernon L. (Vernon Lyman) KelloggDarwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming → online text (page 32 of 38)