The Ghost in the Machine (41 page)

 

 

When the marsupials took to the trees, smell ought to have become
unimportant to them compared to the distance receptors, sight and hearing,
and their nervous system ought to have reflected the change. But in
contrast to our ancestors, the placental tree-dwellers, this change
failed to take place in the marsupials. Moreover, an important component
is lacking in the brain of the higher marsupials, the so-called corpus
callosum. This is a conspicuous nerve tract which, in placentaIs,
connects the 'new' (non-olfactory) areas of the right and left cerebral
hemispheres. It obviously plays a vital integrative part, though the
details of its functioning are still somewhat problematical,* and its
absence from the marsupial brain seems to have been a principle factor
in their arrested development.

 

* Some humans were found at autopsies to have been born without a
true corpus callosum -- yet were apparently none the worse for it.

 

 

The point where that development comes to an end is the koala bear. It
is, to quote Wood Jones again, 'the largest and most perfectly adapted
tree-dwelling marsupial. In bulk we may compare it with the Patas
monkey.' [5] But, compared to the monkey, the koala cuts a very poor
figure: 'In the koala the tree-climber has become a tree-clinger. Hands
have turned into hooks; and fingers are not used for plucking fruit or
leaves or testing novel objects, but for fixing the animal, by virtue
of the long curved claws, to the tree upon which it clings.' [6]

 

 

It cannot do otherwise because its principal sense is still smell,
which is of little use in an arboreal creature. Like Quoodle, the koala
thinks with his nose. His brain weighs only one-seventh of the monkey's;
and most of it is occupied by the smell area which in the monkey has
virtually vanished; while the non-smell areas of the koala have no
corpus callosum to connect them. The koala is the end of the marsupial
line of evolution, left behind clinging to his eucalyptus tree like a
discarded hypothesis -- while his monkey cousin is only the beginning
of the evolution from primate to man. It is a fascinating speculation
whether, if the marsupials had been equipped with a corpus callosum,
they would have evolved into a pouched parallel to man, as they have
evolved into pouched parallels of the flying squirrel and the wolf.

 

 

 

'A Tumorous Overgrowth'

 

 

But before congratulating ourselves on having such a superior brain
which does not strangle our oesophagus or condemn us to live by smell,
we ought to pause and examine the possibility that man, too, might carry
a constructional fault inside his skull, perhaps even more serious
than the arthropod and marsupial precedents; a constructional error
which potentially threatens his extinction -- but which might still be
corrected by a supreme effort of self-repair.

 

 

The first reason for this suspicion is the extraordinary rapidity of
the evolutionary growth of the human brain -- a feat, as we know,
unique in evolutionary history. To quote Professor Le Gros Clark:
'It now appears from the fossil record that the hominid brain did not
begin to enlarge significantly before the beginning of the Pleistocene,
but from the middle Pleistocene [circa half a million years ago] onwards
it expanded at a most remarkable speed -- greatly exceeding the rate of
evolutionary change which had so far been recorded in any anatomical
character in lower animals. . . . The rapidity of the evolutionary
expansion of the brain during the Pleistocene is an example of what has
been termed "explosive evolution".' [7]

 

 

Next, let me quote from Judson Herrick's
The Evolution of Human Nature
:

 

The history of civilisation is a record of slow but dramatic
enrichment of human life interspersed with episodes of wanton
destruction of all the accumulated riches of property and spiritual
values. These episodic reversions to bestiality seem to be increasing
in virulence and in the magnitude of the resulting disasters until
now we are threatened with the loss of everything that has been won
in our struggle for the better life.
In view of this record it has been suggested that the enlargement
of the human brain has gone so fast and so far that the result is
actually pathological. Normal behaviour depends upon the preservation
of a balanced interplay between integrating and disintegrating factors
and between the total pattern and local partial patterns. So, it is
claimed, the human cortex is a sort of tumorous overgrowth that has
got so big that its functions are out of normal control and 'race'
erratically like a steam engine that has lost its governor.
This ingenious theory was published by Morley Roberts and quoted
with apparent approval by Wheeler. [8]  Their arguments seem to
be plausible in view of the past history of wars, revolutions, and
crumbled empires, and the present world-wide turmoil that threatens
total destruction of civilisation. But the theory is neurological
nonsense. [9]

 

In the form stated here it certainly is. It cannot be the
size
of the cortex alone which 'puts its function out of normal control'. We
must look for a more plausible cause.

 

 

The cause which contemporary research seems to indicate is not increase
in size, but
insufficient co-ordination
between archi-cortex
and neocortex -- between the phylogenetically old areas of our brain,
and the new, specifically human areas which were superimposed on it
with such unseemly haste. This lack of co-ordination causes, to use
a phrase coined by P. MacLean, a kind of 'dichotomy in the function
of the phylogenetically old and new cortex that might account for
differences between emotional and intellectual behaviour'. [10] While
'our intellectual functions are carried on in the newest and most highly
developed part of the brain, our affective behaviour continues to be
dominated by a relatively crude and primitive system. This situation
provides a clue to understanding the difference between what we
feel
and what we
know
. . . .' [11]

 

 

Let us look a little closer at what is implied in these statements by
an eminent contemporary neurophysiologist.

 

 

 

The Physiology of Emotion

 

 

The distinction between 'knowing' and 'feeling', between reason and
emotion, goes back to the Greeks. Aristotle in
De Anima
pointed to
visceral sensations as the
substance
of emotion and contrasted them
with the
form
, i.e., the ideational content of the emotion. The
intimate connection between emotion and the viscerae is a matter of
common experience, and has always been taken for granted by laymen and
physicians alike: we know that emotional arousal affects heartbeat and
pulse; that fear stimulates the sweat glands, grief the tear glands,
and the respiratory, digestive, not to mention the reproductive, systems
are all involved in the experience of emotion. So much so that the word
'visceral' was originally used to refer to strong emotional feelings,
including fear ('he has no guts') and pity ('the bowels of mercy').

 

 

Well into the eighteenth century, the medical profession adhered to the
Galenic doctrine, according to which thoughts circulated in the brain,
emotions circulated in the vessels of the body. At the beginning of the
nineteenth century, this ancient dualism yielded to a more modern version:
in his immensely influential books,
Anatomie Générale
and Recherches Physiologiques sur la Vie et la Mort
, Xavier Bichat
drew a fundamental distinction between the cerebro-spinal nervous system,
including the brain and spinal cord, which looked after all the external
transactions of the animal with its environment; and the 'ganglionic',
now called autonomic nervous system, which controlled all organs serving
internal functions. The first was governed by a single centre, the
brain; but the second, Bichat thought, was governed by a great number
of 'little brains', such as the solar plexus, in various parts of the
body. The cerebro-spinal nervous system was held to be responsible for
all voluntary action; the autonomic, governing the viscera, was beyond
voluntary control; and so were the passions or emotions which all belonged
to the visceral domain.

 

 

Bichat's doctrine reigned for a whole century; it was proved wrong
in many, if not most, details; but the distinction he made between
the functions of the two systems, and their correspondence with the
ancient dualism between thought and emotion, is still valid in broad
outlines. Nobody, of course, believes any longer that the experience of
emotion is located in 'little brains' in the vicinity of the heart and
bowels. All experience is centralised in the brain, including the control
of the autonomic system which looks after visceral function. As one would
expect, the viscera are controlled by a phylogenetically very ancient
structure in the brain-stem, the region of the hypothalamus (thalamus:
Greek for inner chamber or woman's apartment). This is the crucial area,
in close proximity to the pituitary gland and to the vestiges of the
primitive smell-brain, which regulates visceral and glandular functions
beyond voluntary control, and is intimately connected with emotional
experience.

 

 

But we must not jump to the conclusion that the hypothalamus itself is the
'seat' of emotion. That would leave out of account the ideational aspect,
and would reduce emotion to 'nothing but' visceral reactions. William
James came in fact very close to this position when, in 1884, he published
an article that launched the famous James-Lange theory of emotions. In a
nutshell, the theory said that in those situations which require visceral
reactions to cope with them (e.g., accelerated heartbeat for running away
from danger), the feeling that one's heart races is the emotion. The heart
does not race because we are frightened; we are frightened because the
heart races; and we do not weep because we feel sad, we feel sad because
we weep. It is the perception of one's own visceral reactions which
lends emotional colouring to experience. The visceral reaction itself is
automatic and unconscious, either innate or acquired by past experience.

 

 

The James-Lange theory gave rise to endless controversies which even
today, eighty years after its launching, have not completely died
down. In 1929 Walter Cannon -- a pioneer in this field -- seemed to
have given the coup de gr�ce to it, when it was shown that emotional
behaviour persists even after the connections between viscera and brain
had been severed. This and other experimental evidence brought the
theory into disrepute.* James' doctrine that emotions are 'nothing but'
visceral reactions has certainly proved untenable; but the very fact
that the doctrine was so hard to kill shows that it contained a hard
core of truth -- the fact, driven home by common, everyday observation,
that diffuse bodily sensations from internal processes which are not
under voluntary control form an essential component of all emotional
experience. Cannon's own theory of emotions (the Cannon-Bard theory)
laid decisive emphasis on the bodily changes in 'emergency reactions'
to hunger, pain, rage and fear, mediated by adrenal hormones and the
autonomic nervous system. But he shifted the focus of attention from the
visceral to the cerebral mechanisms in the hypothalamus which control
them, and regarded the bodily changes as expressions rather than causes
of emotional feeling.

 

* Nevertheless, quite recently Mandler has shown that even the
seemingly decisive evidence (Cannon's famous 'five points') is
open to a different interpretation: 'Although visceral changes are
essential for the initial establishment of emotional behaviour,
on later occasions the emotional behaviour may prove to have
been conditioned to external stimuli, and may occur both without
visceral support and -- in some form -- prior to it. . . . Cannon's
argument that emotional behaviour may be present in the absence of
visceral activity will probably have to be restricted to saying
that it will only be present when intact visceral structures and
responses have previously mediated the link between environmental
conditions and emotional behaviour. . . . Visceral response is
important for the establishment, but not for the maintenance,
of emotional behaviour.' [12]

 

The Cannon-Bard theory was in its turn criticised by Lashley and others;
but at this point the subject becomes too technical. To sum up, we may
safely conclude that emotions are 'overheated drives' (due to internal
and/or external stimulations) which are temporarily -- or even permanently
-- deprived of an adequate outlet; the dammed-up excitement stimulates
visceral and glandular activity, affecting circulation, digestion,
muscle-tone, etc.; and 'the reverberations of the total organism can
then register centrally as felt emotion' (Herrick [13]). Or, to quote
Mandler's more recent survey of the subject: 'As far as the physical
background of emotion is concerned, we can agree with commonsense that
some sort of internal, visceral response accompanies the production of
emotional behaviour.' [14] And there is further evidence that these
visceral responses depend on archaic structures in the brain whose
fundamental pattern has undergone but little change in the whole course
of evolution 'from mouse to man' (MacLean).

 

 

 

The Three Brains

 

 

After this historical excursion, let us return to the question how these
archaic structures, and the archaic feelings to which they give rise,
get along with the brand-new structures and functions in our brains. The
following excerpts lead straight into the problem; they are from a
medical paper by Professor Paul MacLean, who fathered the so-called
Papez-MacLean theory of emotions: