An organism, as living matter, does not stand in opposition to,
or outside of, the rest of the world. It is part of the world. It
receives matter from its surroundings, and gives some back; therefore
it is influenced by its surroundings. It is acted upon, and it reacts
upon the latter, and if these change (and they are nowhere and never
strictly the same) the organism also _varies_. It _adapts_ itself, and
if it does not, or, rather, cannot, do so, it dies, because it is unfit
to live in the world, or, rather, in those particular surroundings
and conditions in which it happens to be. That organism which yields
most easily, accommodates itself most quickly, has the best chance of
existence--_survival of the fittest_. 'Fitness' in this case does not
mean fitness to live, but rather a particular condition which happens
to fit into the new circumstances.
Adaptation and variation are simultaneous: they are fundamentally the
same. If there were no adaptability and no variability, those simplest
of organisms which we suppose to have sprung into existence in the
pre-Cambrian period would long ago have ceased to exist.
It is the physiological momentum which models the organism, and, by
causing its adaptations, has produced its organs by change of function.
Gegenbaur illustrates this most important fundamental truth by an
excellent example. Suppose that, in an absolutely simple organism, all
the parts of its exterior are under the same functional conditions,
so that each part of the surface can take in food, and that this is
digested, assimilated, in the interior. There is, in this condition,
not yet any definite organ. If this organism sinks to the bottom and
becomes sessile, this part is excluded from taking in nourishing
matter, while the opposite surface alone remains, or becomes more, fit
for this function. Thus, a simple variation and adaptation has been
produced, and if the same organism continues in this position, its
bottom cells will estrange themselves from their original function,
while those on the top will convey the food into the interior, where
a cavity will be formed, ultimately with a permanent opening, the
primitive gut and mouth, both very different from the 'foot.'
Thus, by adaptation and variation the organism acquires new functions,
organs, features, and it gives up and eventually loses others. Its
offspring is like it. Like produces like. This is the principle of
_heredity_. Adaptation, when going on generation after generation on
the same lines in the same direction, becomes continuous, and has an
intensifying, _cumulative_ effect. By always weeding out from a flock
of pigeons those birds which possess more dark feathers than the rest,
we ultimately produce an entirely white race. We hurry on what Nature
does slowly.
The inheritance of acquired characters becomes very obvious in the
following example: The Monera are the lowest living organisms known;
they consist of a mass of protoplasm, and are still devoid of even
a nucleus. They multiply simply by division; each half is like the
other, and like the parent (which by this process has ceased to exist),
except that each is smaller and has to grow. A certain Moneron,
_Protomyxa aurantiaca_, is orange-coloured, and its offspring is from
the beginning of the same colour, and this colour has been acquired
by that kind of Monera-like protoplasm which thereby has become the
species called Aurantiaca. We have no reason for assuming that there
existed from the beginning of life not only colourless, but also red,
orange, and other kinds of protoplasm. In these simplest of organisms
the whole process of heredity seems very obvious; but in the higher
ones, in those which propagate by eggs, the problem is infinitely
more complicated. It is true that the egg is, strictly, nothing but
a small part of the parental organism, and we know from everyday
experience that this single egg-cell has in it all the attributes and
characteristics of the parent; but these attributes and characteristics
make their appearance successively, just as the egg cell of a chick has
neither wings nor feathers, not even a backbone, but develops these
organs because its parents have them.
The theory that acquired characters are hereditary has often been
vigorously attacked; but the champions of the negative position have
not given us anything satisfactory instead. They question, also, the
principle of adaptation as a factor in Evolution, and substitute
'variation,' coupled with 'natural selection.'
They point to Darwin's argument: (1) It is a fact that animals and
plants produce a much greater number of young than in their turn grow
up to propagate the race; (2) no two of the frequently many individuals
of the same breed are exactly alike, although the differences may be
hidden to our perception (this is quite true, because no two entities
can live in absolutely the same place and conditions); (3) through
heredity the offspring takes over the faculties and features of the
parents; (4) what decides which of the many individuals (each one
possessing some aberration or variation) are to live and to propagate
the race?--obviously those individual variations which happen to make
the lucky possessors most fit for the struggle for life.
So far, well; but the 'Neo-Darwinians' imagine that 'adaptation'
is not the cause, but the result, the effect, of the formation of
species. According to them, the species are neither adapted by, nor do
they adapt themselves to, their surroundings. Adaptation is to them
an accomplished fact, a condition which a species happens to be in
because its particular variation is the one which, to the exclusion of
others, suits or fits into its surroundings. Such a view simply takes
variation for granted, and stipulates it as a something _a priori_,
without raising the further necessary question, why there should be
any variations at all. Why, indeed, unless they are caused by external
influences? Haeckel elucidated this by the conception of adaptation as
explained in the foregoing pages.
These and kindred speculations have produced some rather curious
discussions, which not infrequently end in conundrums. If we speak of
a case of adaptation as a condition, a fact, we easily run the risk
of getting into confusion about cause and effect. For example: Is the
stag swift because he has long and slender legs, or are his legs long
because he is swift? In reality, swiftness and length of legs are cause
and effect in one. His legs have been so modified as to make him swift,
because he has put them continuously to whatever was his full speed,
which in his thick-footed ancestors was probably a very slow one. The
above question reads, therefore, more sensibly as follows: Has the stag
become swift because his legs have become long and slender, or have his
legs become long and slender because he has attained swiftness? Now, we
see that both halves of the double question are practically the same
and instantly suggest the answer.
A fundamental difference between artificial machines and living
organisms is that the former are worn out by use, while the latter not
only repair the loss caused by use, but are also stimulated to further
increase. On the other hand, organs which are not put into function,
or are not used, _degenerate_. The various cells of the organ react
upon external stimuli by increased activity. Why this should be so is
another question--perhaps because those which do not would soon be not
fit to survive. Each cell has a function; the more specialized the more
intense it is. Every external stimulus, every contact with the outer
surroundings, is an insult, necessarily of detrimental effect, as it
disturbs the equilibrium of the cell body. It must, therefore, be of
advantage to the cells' well-being to return as soon as possible to the
_status quo ante_, and this can only be done by increased activity.
In the present state of our knowledge, we can approach only the
simplest cases of acquisition of characteristics. Mostly they are
so complicated, subject to so many unthought-of conditions, that we
do not know from which end to approach the problem. Frequently the
supposed use of certain obvious features is the merest guesswork. This
applies especially to features to which we are not accustomed (although
wrongly so) to assign a function--for example, coloration. A green
tree-frog will with predilection rest on green leaves. The advantages
of concealment are obvious, and in this case he 'adapts himself' to the
surroundings by making for green localities: if he did not he would
be eaten up sooner than his more circumspect comrades. But this making
for, and sitting in, the green has not _necessarily_ made him of that
colour. Extreme advocates of one view would argue as follows: Once upon
a time there were among the offspring of ancestral tree-frogs some
which, among other colours, exhibited green, not much, perhaps not even
perceptible to our eyes. The occurrence of this colour, according to
them, was spontaneous, a freak--as if in reality there were anything
spontaneous in the sense of being causeless. The descendants of these
more greenish creatures, provided they did not pair with frogs of the
ordinary set, became still greener (by accumulative inheritance), and
so on, until the green was pronounced sufficient to be of advantage
when competition could set in.
With this view there is always the difficulty of understanding how the
initial very small changes can be useful, unless we have to deal with
extremely simple organisms. Is it likely in the case of our frogs that
an almost imperceptible variation in colour makes them more fit to
live? We have to assume that 'luck' or chance kept them for generations
out of harm's reach, until the accumulation of green, hitherto quite
ineffective, neither harmful nor useful, became strong enough to be
effective. Such cases undoubtedly happen.
But we can also argue out this problem in a somewhat different way,
which goes nearer to the root of the whole process. The original
slight, imperceptible change in pigmentation is not a spontaneous
freak; it was caused by the direct influence of the surroundings in
which the particular frogs happened to live, be this factor light or
temperature or food. Thus it stands to reason that the offspring,
living under similar conditions, will be acted upon in the same way.
That factor which has added green to the parents will add green to the
children, until by accumulative inheritance a more decidedly green
race is produced.
The offspring of green plants do not become green when grown in the
dark; the young plants inherit not the green, but the capacity of
becoming green when acted upon by sunlight. This as an instance of
direct influence of the surroundings on a substance (chlorophyll),
which has not yet performed a function. But the kittens of a pair of
black cats produce black hair before they are born, and we have no
reason to doubt that the black pigment in their tegumentary structures
is ultimately referable to the action of the sunlight. In many
instances creatures living for generations in darkness become white,
pigmentless, and they regain it when exposed to light. For example, the
white, colourless Proteus from the caves of Adelsberg becomes clouded
grey, and ultimately jet black, when kept in a tank whence light is not
strictly excluded.
Blindness is a very general characteristic of creatures which dwell in
darkness. There are all stages between total blindness and weak eyes.
Now, do these blind creatures live in darkness because they are blind,
or have they become first weak-eyed and then blind because of the
continuous disuse of their eyes? The former explanation has actually
been suggested! Individuals not smitten, but spontaneously, as a freak,
born with sore eyes, have crept into the darkness for relief and have
produced a blind race! To carry such a notion to the bitter end leads
to absurdities. Anyhow, it is not understandable where the benefit
of losing the eyesight arises. It can be explained only by continued
disuse: witness _Spalax typhlus_, the blind mole, and, above all, the
Endoparasites.
Let us now take an example to explain the influence of a tangible
external stimulus. Repeated pressure produces callosities. Although
they are not exactly beneficial in the shape of corns on our toes,
they are so on our hands. At any rate, the morphologist can trace the
development of the footpads, nails, hoofs, and horns, step by step from
small beginnings. The cells of the Malpighian stratum, of the inner,
active portion of our epidermis, are excited to extra activity, and
by continually producing more horn cells than peel off the surface of
the skin in the normal process of wear and tear cause the formation
of the pad. It need scarcely be mentioned that hypertrophic growths
are not necessarily useful; they are often harmful, and in that case
pathological.
Lastly, a few words about the very difficult question of _teleology_.
In trying to explain Evolution in a mechanical--sometimes called
monistic, but in reality natural--way, we exclude anything like a
set purpose, a goal, or ideal, a final condition which the organism
strives to attain. Unknown, however, to many morphologists, especially
embryologists, their writings are full of this teleological notion.
Indeed, there are many cases in which an organism becomes changed, and
quickly, too, in a way which cannot but be called reasonable. It starts
modifications, be they outgrowths, alterations in shape or colour, or
the making good of injuries received, which by 'short-cuts' produce
the only advantageous result that can reasonably satisfy the new
requirement or altered circumstances.
Trees growing in precarious positions, after part of the supporting
rock has slipped away, throw out new roots, and rearrange some of
the old ones in the only way which could save the tree. In animals
which have lost part of a limb the wound closes up, and what is left
is turned into a serviceable stump--for example, in water-tortoises
(creatures in which reproduction of lost limbs does not happen). In
frogs and newts the lost part is reproduced, not correctly, but in a
good semblance. Tortoises which have had their shell smashed can throw
off an astonishingly large portion and renew the bone as well as the
overlapping scutes; but this mending is not neatly done. It serves the
requirement, but it is patchwork; the new shell is such as no tortoise
ever possessed before.
Mammals transported into colder countries, or subjected to continued
exposure, grow a thicker coat; and the same kind of tree which in a
sheltered valley is tall, large-leaved, and soft-wooded, assumes a very
different aspect, although perhaps growing into a healthy specimen,
when planted on a wind-exposed hill.
There is no room, or, rather, no time, to apply to these cases the
principle of many variations or the long-continued accumulation of
infinitely small changes. The thing is to be done quickly, or not
at all. Nor can we explain the mending of a wound, which implies an
activity of countless cells, simply as a case of, or similar to, the
reproduction of a lost part; against such an explanation militates the
almost absolute unlikelihood of that precise injury having happened
before to any of the creature's ancestors.
Still, I think we are brought near the solution of the mystery by
such considerations. We see no difficulty in the regeneration of a
few cells, or in the making good of the disturbance suffered by one
of the most simple organisms; but we become suspicious when we see
that countless cells, not of one kind, but of the most varied tissues
and parts of the body, make common cause in remedying a defect in a
serviceable way.
We must assume that since the beginning of life organisms have been
subjected to countless insults. We can scarcely speak of a wound in
an Amæba; but these insults have always been made good, and whenever
this was not the case, that particular organism came to an end. As
these organisms developed into more complicated ones, the possible
insults became more serious, more complicated; and the organisms took
adaptive measures so as to be superior to them. This action, I have
no hesitation in declaring, became by heredity a habit. The whole
creature became so thoroughly 'imbued' (for want of a better word) with
the finding of ways and means for meeting sudden, serious conditions,
that it now acts directly, and produces by a short-cut, with the least
amount of time and with the smallest possible waste of material, that
which meets the occasion, thereby saving the life of the individual
and that of the race. This we cannot but call reasonable and to the
purpose, although it is all carried out by _causæ efficientes_ without
there being any _causæ finales_.