The Act of Creation (62 page)

p. 435
) is represented
by the muscular structure of the limb, plus the 'canal-system' of nervous
pathways leading into it, and includes the apparatus -- whatever its
nature -- which accounts for the selectivity of the response by enabling
muscles to analyse incoming impulses. The
code
is the sequence
of excitation-clangs which calls forth one complete motion -- say,
one step of the limb. Members of the matrix are the several joints
on the next-lower level No. 3, which are triggered off in a pre-set
order by their sub-codes, i.e. by the appropriate components of the
excitation-clang. We may remember by way of analogy, how part-sequences
of the genetic code are triggered into action in a pro-set order.

 

 

The 'motor unit' at the bottom of the hierarchy responds according to the
all-or-nothing rule, but the musculature of a joint is capable of graded
responses, and the motions of the whole limb follow a flexible strategy
-- shorter or longer step, swift or groping -- dependent on the input
from the environment. Weiss accounted for these variations by proposing
that the excitation-clang 'is constantly fluctuating in its composition',
and thus determines which single muscle should be activated at any given
moment. But this conception does not seem to agree well with the basic
principle that centres on high levels do not deal directly with units on
low levels of the hierarchy. A way out of this difficulty is to be found
in suggestions by Ruch (1951) and Miller et al. (1960), according to which
pre-set patterns of skilled movements are triggered off as units by the
brain; but the signal -- i.e. the 'excitation clang' -- would merely
'rough in' the sequence of movements 'and thus reduce the troublesome
transients involved in the correction of movement by output-informed
feedbacks'. [15] Since feedback circuits must be assumed to operate on
every level, down to the single cell, the adjustment of the details of
the 'roughed-in' movement could be handed over to lower levels. Miller et
al. have made the further suggestion that this handing-down procedure may
be the equivalent of converting an order coded in a 'digital' language,
into a graded, 'analogue' output. The excitation-clang could thus consist
in a series of 'on', 'off' signals like the dots and dashes of the Morse
code; but each sub-unit could respond to its specific 'on' signal by a
'more' or 'less' intense activity, dependent on local conditions (see also
below, pp. 569 ff.). These are speculations, and offered by their authors
as such; but there are various alternative possibilities to account
for the 'filling in' of details which were left open in the generalized
excitation pattern, by feedback devices on successively lower levels.

 

 

 

Limits of Control

 

 

In the experiments previously discussed, a super-numerary limb was
grafted next to a normal one, facing in the same direction. In another
series of experiments Weiss exchanged and reversed the position of the
limbs of newts. The result is again best described in his own words:

 

The essential independence of the structure of motor activity is
dramatically demonstrated when one exchanges and reverses the limbs
of animals and then finds them crawling backwards whenever they aim to
crawl forwards and vice versa. . . . This has been done in the developed
animal, but the same operations have been done in embryos, and these
animals have then functioned in reverse from the very beginning. What
more spectacular expression can there be of the intrinsic primacy of
the motor patterns of behaviour for which the external input acts only
as a selective trigger? [16]

 

In other transplant experiments, only the position of the two fore-limbs
was interchanged and reversed:

The grafted limbs moved just as they would have done had they been
left in their original position, causing backward motion when the rest
of the animal was trying to move forward, and forward motion when
the rest of the animal was trying, for example, to avoid a noxious
stimulus presented in front of it. A year's experience did not change
this reversed movement of the grafted legs. [17]

 

The experiment beautifully illustrates the autonomy of the limb-matrix.
As in the fifth-limb experiment, the nerves growing out of the stump
reached the muscles of the grafted limb in a random manner. Once more,
the graft-limb achieved perfectly coordinated motion, thanks (we assume)
to the analyser devices in the muscles which respond to one component
in the clang signal only. But since the limb was grafted in reverse,
it has to step in reverse. No doubt the poor creature senses that
something is wrong if its fore-limbs move backward and the back limbs
move forward. But owing to the principles Of hierarchic order, the centre
which co-ordinates the movements of the animal as a whole -- level 5 in
Weiss's schema -- cannot interfere with the functioning of the analyser
devices on level 2, to reverse their responses. It apparently cannot even
prevent excitation-clangs being triggered off automatically by level
4 to the useless limbs. And when the excitation reaches the latter,
they respond as they must. We have here a first, artificially produced
example of 'faulty integrations' which will occupy our attention later on.

 

 

The example further illustrates a point mentioned before:
a matrix on
the n-level is represented on the n+1 level by its code
. There is,
under normal conditions, no direct commerce between its members on the
n-1 level, and the co-ordinating agency on the n+1 level. If the latter
interferes directly with the former, routines become disorganized,
and we get the 'paradox of the centipede'. Loss of direct control over
automatized processes on lower levels of the body hierarchy is part of
the price paid for differentiation and specialization. The price is of
course worth paying so long as the species lives in an environment that
is fairly stable. It is after all not part of the normal destiny of the
salamander to encounter Dr. Paul Weiss.

 

 

 

NOTES

 

 

To
p. 431
. The validity of Coghill's findings for
a whole range of other species -- cat, bird, man -- was demonstrated
in a general way by authors like Coronios (1933), Herrick (1929), Kuo
(1932). However, some geneticists (e.g. Windle and his associates) have
maintained that functional co-ordination in higher species is the result
of additive chaining of specialized local reflexes. As against this,
Hooker (1950) has pointed out the undisputed fact that motor nerves
are functional before the sensory nerves, and that the sensory and
intercallated neurons in the reflex arc are the last to become functional,
which amounts to an indirect refutation of the reflex summation view. For
a summary of this controversy see Thorpe (1956) pp. 20 ff. and p. 45;
also Barton (1950) and Hooker (1950).

 

 

On the other hand, Tinbergen has shown that in some patterns of
complex instinct behaviour (e.g. nest building, Kortlandt, 1940), the
part-performances which go into the total pattern emerge at different
times, following 'a fixed time pattern just as with growing morphological
structures' (Tinbergen, 1951, p. 136). Thus, for instance, fastening
of twigs in the nest precedes searching for twigs. The existence of
'internal clocks' which regulate the serial activation of the various
sub-codes of the integrated performance is entirely in keeping with
the total pattern view. Thorpe concludes: 'Embryological studies now
suggest that ontogenetically, complex muscle co-ordinations resembling
fixed action patterns [see below] precede responses of the simple reflex
type in mammals.' Cf. next note.

 

 

 

To
p. 432
. This confusion may have been a
contributing factor in the controversy mentioned in the previous
note. Since myogenic muscle contractions can be produced in embryos by
electrical or mechanical stimulation before neuro-muscular integration is
established, the 'isolated reflex-school' assumed such pseudo-reflexes
to be true reflexes and the primary elements of adult behaviour. See,
e.g. Thorpe, loc. cit.

 

 

 

To
p. 434
. The Hixon Symposium was one of the
most fertile exchanges ever held between leading experts in various
disciplines. Among its partialpants were H. Kluver, Wolfgang Köhler,
K. S. Lashley, W. S. McCulloch, John V. Neumann, R. W. Gerard, Lorente
de Nó, Paul Weiss, Linus Pauling, etc., to mention only a few. No
wonder that Weiss, carried away by enthusiasm after hearing Lashley's
brilliant paper on 'The Problem of Serial Order in Behaviour', concluded
with expressing his hope that today's 'discussion will mark a turning
point in the building of neurological theories'.

 

 

To
p. 436
. To make matters a little more
complicated, we may remind ourselves in passing that muscle-contractions
serve not only motility but also maintenance of tone and temperature
in the organism; sometimes they serve only the last function alone
(in shivering) since muscle is a main source of animal heat.

 

 

To
p. 436
. At the time of writing this theory
still has certain difficulties to overcome; among them the fact that
the energy supply of the fibre depends not only on ATP itself but also
on creatin phosphate.

 

 

 

 

 

III
DYNAMIC EQUILIBRIUM AND REGENERATIVE POTENTIAL
Acting and Reacting
'The organism', to quote Coghill once more, 'acts on the environment
before it reacts to the environment.' This statement seems to apply to
every level and every aspect of organic life. The lowliest creature
and the highest, the moment it is hatched or born, lashes out at the
environment, be it liquid or solid, with cilia, flagellae, or contractile
muscle fibre; it crawls, swims, glides, pulsates; it kicks, yells,
breathes, feeds, and sucks negative entropy from its surroundings for
all it's worth.
The patterns of these built-in motor activities we saw to be to a
large extent autonomous; 'the structure of the input does not produce
the structure of the output, but merely modifies it.' Moreover, the
input itself is actively controlled and modified by the central nervous
system from the moment it impinges on the peripheral receptor organs; and
recent developments have caused, at least among an unorthodox minority of
psychologists, a distinct 'shift from the notion that an organism is a
relatively passive, protoplasmic mass whose responses are controlled by
the arrangement of environmental stimuli to a conception of an organism
that has considerable control over what will constitute stimulation.' [1]
Even below the level of the single cell, organelles such as the
mitochondria and kinetosomes carry on their autonomous activities; their
shadowy patterns under the electron-microscope are a reminder that the
emergence of life means the emergence of spontaneous, organized exertion
to maintain and reproduce originally unstable forms of equilibrium in a
statistically improbable system in the teeth of an environment governed by
the laws of probability. The live organism succeeds in this by creating
an inner environment with which to confront the outer environment --
and in which the law of entropy seems to be reversed, biological clocks
replace astronomical clocks, and hierarchic order reigns supreme.
An organism is said to be 'well balanced' or 'well adapted' or 'in
dynamic equilibrium' if it has established a modus vivendi between
its internal and external environment. This, of course, is a more
complex form of balance than mechanical or chemical equilibrium; it
implies metabolic processes required for the maintenance of form and
function in an open system in perpetual flux -- Bertalanffy's (1941)
Fliessgleichgewicht
; it implies self-regulating devices which
keep irritability and motility within a safe standard range; and it
also implies the slow, cyclic changes of morphogenesis, maturation, and
reproduction, regulated by biological clocks. If all these processes are
to be lumped together under the portmanteau word 'adaptation', then we
must call it adaptation of a special kind, on the organism's own terms;
after all, the perfect adaptation of an organism to the temperature and
chemistry of the environment is to die. In fact, the animal does not
merely adapt to the environment, but constantly adapts the environment
to itself. It eats environment, drinks environment, fights and mates
environment, burrows and builds in the environment; and even in observing
environment, it modifies, dismantles, analyses, and reassembles it after
its own fashion, converting 'noise' into 'information'. 'Perception',
Woodworth wrote, 'is always driven by a direct, inherent motive which
might be called
the will to perceive
.'
Thus the terms 'adaptation', 'environment', 'equilibrium' will be used
in the following pages not in their usual passive connotations, but
with active overtones, as it were. Instead of treating an animal as a
'relatively passive, protoplasmic mass whose responses are controlled
by the arrangement of environmental stimuli' -- a Pavlov-dog in its
restraining harness -- we shall regard it as a relatively self-contained
organism, deploying spontaneous activities simultaneously on various
levels of its constituent functional hierarchies -- activities which
are triggered and modified, but not created by the environment.
What is Equilibrium?
An organism can be said to function normally so long as the stresses
between internal and external milieu do not exceed a certain standard
range. To simplify the argument, let the term 'internal milieu' embrace
all processes within the organism, and let us lump together the nature,
intensity, and duration of environmental excitations in a single
variable. We shall then be able to distinguish between (a) 'normal',
(b) 'paranormal' or 'traumatic', and (c) destructive environmental
conditions -- though, needless to say, the boundaries between them cannot
be sharply defined.
The term 'dynamic equilibrium' shall apply only to a normal organism
functioning under 'normal' conditions. Under these conditions the
organ-systems, organs, and organ-parts of the animal perform their
specific, autonomous functions as sub-wholes, at the same time submitting
to the regulative control imposed by the higher centres. The control
is exercised by excitatory and inhibitory processes, but the latter
play a vastly greater part. From the moment of conception, the genetic
potentials of the individual cell are further restrained with every step
in differentiation; and on every level of the growing and mature organism
inhibitory blocks, negative feedbacks, growth-inhibiting hormones are
at work. In the nervous system, in particular, there is censorship at
every step -- to prevent overloading of the information channels and
overshooting of responses. Without this hierarchy of restraints, the
organism would instantly blow its fuses in a kind of delirium agitans
and then collapse.
Under normal conditions the part will not tend to escape the restraining
influence of the whole. Under paranormal conditions the balance
is upset. Thus the term 'balance' or 'equilibrium' takes on a special
meaning in the context of an organic hierarchy: it is not meant to refer
to relations between parts on the same level of the hierarchy, but to
the relation of a part to its controlling centre on the next higher
level. The stresses arise not between inputs 'competing for the final
common path,' as the expression goes, not between 'antagonistic drives'
or 'conflicting impulses' (which do not directly communicate with each
other and cannot 'fight it out among themselves') -- but between the
excited part and the whole, whose attention it is trying to monopolize:
in other words,
between the self-assertive tendencies of the part
and the restraints imposed by the controlling centre
. Equilibrium is
maintained in the organism by rules comparable to the procedure in a law
court where the opposing parties address themselves not to each other,
but to the judge.
This interpretation of equilibrium in a hierarchy was suggested in my
Insight and Outlook
(p. 139 seq.), and independently proposed
by Tinbergen. In discussing the competition between various 'fixed
response patterns' in innate behaviour, Tinbergen wrote: 'It should
be emphasized that it is quite possible that these interconnections
[between the competing centres] do not in reality run directly from one
centre to the other, but go by way of the superordinated centre.' [2]
Thorpe has expressed similar ideas. [3]
Super-Elasticity and Regenerative Span
An organism lives by constant transactions with the environment. As
a result, stresses are set up in the parts or organs which have been
aroused to carry out the transaction. The excited part may tend to 'get
out of control', i.e. to assert its autonomy against the restraints
imposed on it; it may tend to act to the detriment of the whole. In a
'normal' environment, these tensions between part and whole are of a
transitory nature, and equilibrium is restored with the completion of
the transaction. Under paranormal conditions -- traumatic challenges --
this is not the case, and only what one might call 'adaptations of the
second order' can restore the balance. The animal's capacity to recover
from such traumatic challenges is its regenerative potential.
A stable, monotonous environment tends to produce stereotyped and
automatized reaction-patterns. A variable environment calls for flexible
strategies, for behavioural matrices with sufficient degrees of freedom
to cope with the changing conditions. Paranormal challenges call for
a kind of super-flexibility, for adaptations of a second order which
enable the animal to carry out major reorganizations on several levels
of its structural or functional hierarchies. The range of this ability
constitutes the animal's 'regenerative span'.
The regenerative span of a species thus provides it with an additional
safety device in the service of survival, which enters into action when
the limits of dynamic equilibrium are exceeded -- as the shock-absorbers
of a motor-car take over when the range of elasticity of the suspension
springs is exceeded. But it is more than a safety device. Regeneration
has been described as 'one of the more spectacular pieces of magic in
the repertoire of living organisms'. [4] That may be the reason why it
is so difficult to find a satisfactory definition which would embrace
the whole range of phenomena to which the term is applied.
These include (a) the replication of entire individuals by asexual
reproduction (fission and budding); (b) the reconstitution of a whole
organism from its broken-up fragments, or from a single fragment. Sponges
and hydra can be disintegrated into small clumps or even single
cells by forcing them through a fine filter mesh, yet will reorganize
themselves into normal, complete individuals. A single tentacle of a
sweet-water polyp is capable of regenerating a complete individual;
and transverse slices of a flatworm, taken from any part of its body,
will regenerate the whole animal -- including, brains, eyes, genitalia,
and other complex organs which the segment did not contain. (c) Among
the higher animals, crustaceans are capable of regenerating single
organs exposed to accidental damage (antennae, stalk-eyes, etc.); among
vertebrates, salamanders and newts are capable of regenerating limbs,
eyes, tails, and some inner organs (lungs and gonads); the process in
these cases follows closely the processes of embryonic development. (d)
Equipped with high regenerative powers, some animals practise autotomy --
the self-amputation of an exposed structure in the grasp of an enemy,
which is subsequently replaced. Lizards let go of their tails; crabs,
insects, and spiders of their legs or antennae, starfish cast off an
arm. Self-amputation is facilitated by a 'breaking plane' of weakened
structure somewhere near the base of the expendable appendage -- rather
like the perforations between stamps. (e) Among mammalia, regeneration
is generally limited to the repair of damaged bone, muscle, skin, and
peripheral nerves. (f) Lastly, the term 'physiological regeneration'
is used for the routine replacement of tissues used up by ordinary wear
and tear.
Thus regeneration appears to serve two different functions: on the one
hand normal, asexual reproduction, on the other, the restoration of organs
and structures lost by accidental mutilation or by wear and tear. But
the two functions are in fact continuous; they shade into each other,
and are often undistinguishable. If a flatworm sponttaneously sheds
its tail, then grows a new tail and the shed tail grows a new head,
this is called asexual reproduction; if it is sliced into two in the
laboratory it is called regeneration; and the same goes for budding,
which is the natural way of reproduction of some marine coelenterates,
but can be artificially induced by laceration of the body wall. The
'regenerative field' in the salamander's amputated leg-stump obeys the
same type of code as the morphogenetic field of embryonic primordia. And
vice versa: the development of twins or triplets following accidental
fragmentation might as well be called a regenerative process. Hence,
ontogenesis may be described as the regeneration of a complete
individual from a fragment specially set aside for that purpose. But this
'setting apart' of undifferentiated embryonic cells which 'specialize
in non-specialization' occurs in regenerative processes too -- for
instance, in annelids, hydra, and flatworms, which store 'reserve cells'
or 'regeneration cells' in various parts of their bodies and mobilize
them when the need arises. Sexual reproduction thus appears merely as
an added twist to asexual regeneration -- though a twist with momentous
consequences. Instead of replicating a single genetic code ad infinitum,
the bisociation of two genetic codes is the basic model of the creative
act.
Although closely related species on the same level of the evolutionary
hierarchy may differ widely in their regenerative power, it is
nevertheless true that, in a general way, this power decreases as
we proceed from lower to higher organisms. The essence of organic
regeneration is a release of genetic cell potentials which are normally
inhibited in adult tissue.
Physiological Isolation