depends on training; it is only strengthened in each individual by
training, but it depends on an innate predisposition to creep up
to the game, and is thus a form of the hunting instinct. Man has
taken advantage of this, and has increased it, but has certainly not
ingrafted it into the breed by whipping. And something similar will be
found to be true in all cases of so-called inheritance of the effects
of training. It must not be forgotten what astounding results can
be achieved in the individual by training. The elephant is the best
example of this, for it only exceptionally breeds in captivity, and
all the thousands of 'domesticated' elephants in India are tamed wild
elephants. Yet they are as gentle and docile as the horse, which has
been domesticated for thousands of years; they perform all kinds of
tasks with the greatest patience and carefulness, in many cases without
being under constant superintendence. They are indeed animals of great
intelligence; they understand what is required of them, and they
accommodate themselves readily to new conditions of life.
The attachment of the dog to its master and to Man generally has
often been cited as a proof of the origin of a new instinct by the
inheritance of acquired habitude; but the dog is a sociable animal
even in a wild state, and by living in co-operative association with
Man it has transferred its sociable affections to him. We find exactly
the same thing in the elephant which has been caught wild and tamed.
It is particularly emphasized by those who have accompanied animal
transports in Africa that the young elephants are wild and malicious
towards the blacks who teased and maltreated them, but complaisant and
harmless towards the whites who treated them kindly. The attachment of
elephants to their keepers and to every one who shows them kindness is
familiar enough; it does not depend on a newly acquired impulse, but
on the sociable impulse inherent in the species, which, in the wild
state, causes them to live in fairly large companies, and on their
inoffensive, timid, and, we may almost say, affectionate disposition.
Of course it is easy enough to give an imaginative theoretical
interpretation of the origin of a new instinct from a newly acquired
habit. We have often heard that sailors have found the birds in distant
uninhabited islands quite free from fear; they let themselves be struck
down with cudgels without attempting to escape. The extermination of
the Dodo three centuries ago is a well-known example of this. Chun, in
his magnificent work on the German Deep Sea Expedition of 1898, has
recently communicated numerous interesting examples of the indifference
of birds towards Man when they have not learned what his presence
means: thus the sea-birds of Kerguelen, penguins, cormorants, gulls,
'kelp-pigeons' (_Chionis_), and others, behaved towards Man very much
like the tame geese of our poultry yards. Even enormous mammals like
the 'sea-elephant,' a seal with a proboscis-like prolongation of the
nose, neither attempted to escape nor showed any hostility to man, but
quietly let itself be caught. Similar tales were told by Steller in
1799, after he had been obliged to pass a winter with his sailors on an
island in the Behring Straits. The numerous gigantic sea-cows (_Rhytina
stelleri_) which lived there were so confiding that they allowed the
boat to come quite up to them, and the sailors were able to kill many
of them from time to time, using their flesh for food. But towards the
end of the winter the animals began to be shy, and, in the following
winter, when other sailors to the polar regions endeavoured to hunt
them too, it was very difficult to secure them; they had recognized
man as an enemy, and fled from him when they saw him from afar. Thus
the same individuals which had earlier carelessly allowed man to come
up to them now avoided him as an enemy. _This was not instinct, it was
a behaviour controlled by the will and founded on experience._ But it
would soon become 'instinctive' if the meeting with the enemy were
often repeated, just like the winding-up of a watch, which is often
done at a wrong time, for instance, on changing clothes during the day,
and thus without reflection. It is quite easy to conceive that if the
material brain-adaptation which causes flight without reflection at
the sight of man were transmissible, the flight-instinct might become
a congenital instinct in the species in question. But this assumption
is unfounded; for, as is shown by the case of the sea-cow, we do not
require it where the animal is of sufficient intelligence to perform by
its own discernment the action necessary to its existence. The action
may thus become 'instinctive' through exercise and imitation in the
_individual_ life, without however attaining to transmissibility.
But in many cases this is not enough, namely, in all cases in which the
degree of intelligence is not sufficiently high, or where the flight
movement must follow so rapidly that it would be too late if it had to
be regulated by the will, as, for instance, the shutting of the lids
when the eye is threatened, or the flight of the fly or the butterfly
when an enemy approaches. Both fly and butterfly would be lost in every
case if they had voluntarily to set the flight-movement going after
they became conscious of danger. If they had first of all to find
out from whom danger threatened no individual would escape an early
death, and the species would die out. But they possess an instinct
which impels them to fly up with lightning speed, and in an opposite
direction, whenever they have a visual perception of the rapid approach
of any object of whatever nature. For this reason they are difficult
to catch. I once watched the play of a cat, ordinarily very clever at
catching, as she attempted to seize a peacock-butterfly (_Vanessa Io_),
which settled several times on the ground in front of her. Quietly and
slowly she crept within springing distance, but even during the spring
the butterfly flew up just before her nose and escaped every time, and
the cat gave it up after three attempts.
In this case the beginning of the action cannot lie in a voluntary
action, for the insect cannot know what it means to be caught and
killed, and the same is true of innumerable still lower animal forms,
the hermit-crabs and the Serpulids, which withdraw with lightning
speed into their houses, and so forth. It seems to me important
theoretically, that the same action can be liberated at one time by
the will, at another by the inborn instinct-mechanism. In both cases
quite similar association-changes in the nerve-centres must lie at
the root of the animal's action, but in the first case these are
developed only in the course of the individual life by exercise, while
in the second they are inborn. In the former, they are confined to the
individual, and must be acquired in each generation by imitation of
older individuals (tradition) and by inference from experience, in the
latter they are inherited as a stable character of the species.
It has been maintained by many that the origin of instincts
through processes of selection is not conceivable, because it is
improbable that the appropriate variations in the nervous system,
which are necessary for the selective establishment of the relevant
brain-mechanism, should occur fortuitously. But this is an objection
directed against the principle of selection itself, and one which
points, I think, to an incompleteness in it, as it was understood by
Darwin and Wallace. The same objection can be made to every adaptation
of an organ through natural selection; it is always doubtful whether
the useful variations will present themselves, as long as they are
due solely to chance, as the discoverers of the selective principle
assumed. We shall attempt later to fill up this gap in the theory,
but, in the meantime, I should like to point out that the process
of selection offers the only possible explanation of the origin of
instincts, since their origin through modifications of voluntary
actions into instinctive actions, with subsequent transmission of the
instinct-mechanism due to exercise in the individual life, has been
shown to be untenable.
If any one is still unconvinced of this, I can only refer to the cases
we have already discussed of instincts which are only exercised once
in a lifetime, since, in these, the only factor that can transform
a voluntary action into an instinctive one is absent, namely, the
frequent repetition of the action. In this case, if any explanation
is to be attempted at all, it can only be through natural selection,
and as we have assumed once for all that our world does admit of
explanation, we may say, _these instincts have arisen through natural
selection_.
Even though it may be difficult to think out in detail the process of
the gradual origin of such an instinctive activity, exercised once in
a lifetime, such as that, for instance, which impels the caterpillar
to spin its intricate cocoon, which it makes only once, without ever
having seen one, and thus without being able to imitate the actions
which produce it, we must not push aside the only conceivable solution
of the problem on that account, for then we should have to renounce
all hope of a scientific interpretation of the phenomenon. We may
ask, however, whether there is not something lacking in our present
conception of natural selection, and how it comes about that useful
variations always crop up and are able to increase.
But if we must explain, through natural selection, such complex series
of actions as are necessary to the making of the cocoon of the silkworm
or of the Saturnia moth (_Saturnia carpini_), what reason have we
for not referring other instincts also to selection, even if they be
repeated several times, or often, in the course of a lifetime? It is
illogical to drag in any other factor, if this one, which has been
proved to operate, is sufficient for an explanation.
Thus, as far as instincts are concerned, there is no necessity to
make the assumption of an inheritance of functional changes, any more
than there is in regard to any purely morphological modifications. As
the instincts only exercised once show us that even very complicated
impulses may arise without any inheritance of habit, that is, without
inheritance of functional modification, so there are among purely
morphological characters not a few which, though effective, are purely
passive, which are of use to the organism only through their existence,
and not through any real activity, so that they cannot be referred
to exercise, and therefore cannot be due to the transmission of the
results of exercise. And, if this be the case, then transformations
of the most diverse parts may take place without the inheritance of
acquired characters, that is, of functional modifications, and there is
no reason for dragging in an unproved mode of inheritance to explain
a process which can quite well be explained without it. For if any
part whatever can be transformed solely through natural selection,
why, since there is general variability of all parts, should this be
confined to the passive organs alone, when the active ones are equally
variable, and equally important in the struggle for existence?
There are, indeed, many of these passive parts among animals; I need
only recall the coloration of animals, the whole set of skeletal parts,
so diversely formed, of the Arthropods, the legs, wings, antennæ,
spines, hairs, claws, and so on, none of which can be changed by the
inherited results of exercise, because they are no longer capable of
modification by exercise; they are ready before they are used; they
come into use only after they have been hardened by exposure to the
air, and are no longer plastic; they are at most capable of being
used up or mutilated. Finally, even so convinced an advocate of the
Lamarckian principle as Herbert Spencer has stated that among plants
the great majority of characters and distinctive features cannot be
explained by it, but only through the principle of selection; all the
diverse protective arrangements of individual parts, like thorns,
bristles, hairs, the felt-hairs of certain leaves, the shells of nuts,
the fat and oil in seeds, the varied arrangements for the dispersal
of seeds, and so on, all operate by their presence alone, not through
any real activity which causes them to vary, and the results of which
might be transmitted. An acacia covered all over with thorns seldom
requires to use its weapons even once, and if a hungry ruminant does
prick itself on the thorns it is only a few of these which are thus
'exercised,' the rest remain untouched.
But since all these parts have originated notwithstanding their
passivity, there must be a principle which evokes them in relation to
the necessities of the conditions of life, and this can only be natural
selection, that is, the self-regulation of variations in reference to
utility. And if there is this principle, we require no other to explain
what is already explained.
I can quite well understand, however, that many naturalists, and
especially palæontologists, find it difficult to accept this
conclusion. If we think only of those parts that actively function,
and thus change by reason of their function, being strengthened by use
and weakened and diminished in size by disuse, and if, further, we
follow these parts through the history of whole geological epochs, we
may certainly get the impression that the exercise of the parts has
directly caused their phyletic evolution. The direction prescribed by
utility in the course of the individual life and in the phylogeny is
the same, and the intra-selection, that is, the selection of tissues
within the individual animal, leads towards the same improvements
as the selection of 'persons.' Thus it appears as if the phyletic
variations followed those of the individual life, while in reality the
reverse is true; the changes arising from variations in the _germ are
primary, and they determine the course of phylogenesis_, while the
tissue-selection in the individual life only elaborates and improves,
according to the demands made upon it, the material afforded by the
primordial equipment of the germ.
The American palæontologist, Osborn, cites the case of the horse's
feet as an example in support of his view that modification brought
about by use in the individual life must be transmitted in order that
the phyletic transformations may be brought about, but this example
is perhaps the best that could be chosen to prove the contrary. He
supposes that, in every young horse, the means of locomotion are
improved at every step, so to speak, through the contact with the
ground, and I am quite willing to admit that this is so. But that only
proves that, even now, an elaboration and improvement of the equipment
which the germ affords is indispensable, as it has been at all times
and in all animals, and thus that, notwithstanding the enormous number
of generations which our modern horse has behind it, the functional
acquirements of the individual have not yet been impressed upon the
germ. Why not? Because the horse becomes perfect without this, and
there was no reason why personal selection should perfect the primary
constituents of the germ still further, since the finishing touch of
perfection through use is readily afforded by the conditions of each
individual life.
Moreover, when Osborn, Cope, and other palæontologists emphasize that,
in phyletic evolutionary series, _definite paths of evolutionary_
change are adhered to, and are not deviated from either to right or to
left, they are undoubtedly right, but the conclusion which they draw is
not justifiable, whether they assume with Nägeli that there is a power
of development, a principle of perfecting, or whether, as Osborn does,
they assume the transmission of the modifications brought about through
use in the individual life. There remains a third possibility, that
the quiet and constant evolution in a definite direction is guided by
selection, and as, in passively useful parts, that principle alone is
admissible, I see no justification for assuming it to be inoperative
in regard to those which are actively functional. All these variations
which have led up, for instance, to the modern form of the horse's foot
are useful; if they were not, they could not have been produced either
by use or by disuse in the individual life.
At the same time, here again, we are justified in inquiring whether the
assumption of 'chance' germinal variations, which we have hitherto made
with Darwin and Wallace, affords a sufficient basis for selection.
Osborn says very neatly in this connexion, 'We see with Weismann and
Galton the element of chance; but the dice appear to be loaded, and in
the long run turn "sixes" up. Here arises the question: What loads the
dice?'
Until recently we might have answered, 'external conditions'; it is
they that load the dice one-sidedly, and condition that the same
straight path of phylogenesis is adhered to, and exactly the same
direction of variations is preferred and maintained. It has to be
asked, however, whether this answer, which is certainly not absolutely
incorrect, is sufficient by itself, whether the dice are not falsified
and one-sidedly loaded in another sense, so that they always throw a
preponderating number of the useful variations. We shall attempt very
soon to solve this problem, but in the meantime I must refer to another
argument in favour of assuming the Lamarckian principle, perhaps
the most important and it may be thought the most difficult of all
to refute, the so-called co-adaptation of the parts of an organism,
that is, the fitting together of many individual organs for a common
purposeful functioning.
LECTURE XXIV
OBJECTIONS TO THE THESIS THAT FUNCTIONAL MODIFICATIONS ARE NOT
TRANSMITTED
Giant stag as an example of co-adaptation or 'harmonious
adaptation'--This occurs even in passively functioning parts--Skeleton
of Arthropods--Stridulating organ of ants and crickets--Limbs
of the mole-cricket--Wing-venation--Colorations which form
mimetic pictures--Harmonious adaptations in worker-bees and
ants--Degeneration of their wings and ovaries--The quality of food
acts as a liberating stimulus--Vom Rath's case of drones fed with
royal food--Transition-forms between females and workers--Wasmann's
explanation of these--The Amazon ants--Two kinds of workers--Appendix:
Zehnder on the case of ants--On the skeleton of Arthropods--Hering's
interpretation of Ehrlich's Ricin experiments--Hering's position in
regard to the transmission of functional modifications.
It was Herbert Spencer, the English philosopher, who first brought
the argument of co-adaptation into the field against my view of the
non-inheritance of functionally acquired modifications. He pointed
out that many, if not, indeed, most modifications of bodily parts, to
be effective, implied further changes, often very numerous, in other
parts, and these latter must therefore have changed _simultaneously_
with the part which was being changed under the control of natural
selection; this, however, is only conceivable as due to an inheritance
of the changes caused by use, since a simultaneous alteration of so
many parts through natural selection would be impossible. If, for
instance, the antlers of our modern stag were to grow to the size of
those of the Giant Stag of the Irish peat-bogs, which measured over
ten feet across from tip to tip, this would mean--as has already been
shown--a simultaneous thickening of the skull, and to bear the heavy
burden, a strengthening of the _ligamentum nuchæ_, of the muscles of
the neck and back, of the bones of the legs and their muscles, and,
finally, of all the nerves supplying the muscles; and how could all
this happen simultaneously with, and in exact proportion to the growth
of the antlers, if it depended--as natural selection assumes--on chance
variations of all these parts? What if the appropriately favourable
variation in one of these organs did not occur? A harmonious variation
of all the parts--bones, muscles, nerves, ligaments--which unite in a
common activity, is an inadmissible assumption, because, in many cases,
such co-operating groups of organs have in the course of evolution
developed in opposite directions. In the giraffe, for instance, the
fore-legs are longer than the hind-legs, which is the reverse of what
obtains in the majority of ruminants; in the kangaroo the hind-legs,
on the contrary, have developed to a disproportionate size, while
the fore-legs have degenerated into relatively small grasping arms.
Co-operating parts, like the fore and hind limbs, may thus follow
opposite paths of evolution; their variations need not always be
directed to the same end.
The difficulty presented by these so-called co-adaptations or
harmonious correlations cannot be denied, and we must also admit
that, if the results of exercise were inherited, the explanation of
the phenomenon would, in many cases--but not, indeed, in all--be
easy, because the adaptation of the secondarily varying parts in each
individual life would correspond exactly to the altered function of
the part, and would be transmitted to the descendants, and in them
would again be subject to such a degree of variation, according to the
principle of histonal selection, as might be conditioned by the further
progress of the primary variation. The simplicity of the explanation
is striking, if only it were at the same time correct! But there are
whole series of facts, or rather of groups of facts, which prove that
the causes of co-adaptation do not lie in the inheritance of functional
modifications, and this must be recognized, even though we may not
yet be in a position to state the causes of co-adaptation, and to say
whether natural selection suffices to explain it or not.