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further consequence of it.

4

So far we have moved in the realm of facts, attested by the historical
record and the anthropologist's research into prehistory. As we turn from symptoms to causes we must have recourse to more or less speculative
hypotheses, which again are interrelated, but pertain to different
disciplines, namely, neurophysiology, anthropology and psychology.

The neurophysiological hypothesis is derived from the so-called
Papez-MacLean theory of emotions, supported by some thirty years of
experimental research.* I have discussed it at length in The Ghost
in the Machine , and shall confine myself here to a summary outline,
without going into physiological details.
* Dr Paul D. Maclean is head of the Laboratory of Brain Evolution and
     Behaviour, National Institute of Mental Health, Bethesda, Maryland.

The theory is based on the fundamental differences in anatomy and function
between the archaic structures of the brain which man shares with the
reptiles and lower mammals, and the specifically human neocortex, which
evolution superimposed on them -- without, however, ensuring adequate
coordination. The result of this evolutionary blunder is an uneasy
coexistence, frequently erupting in acute conflict, between the deep
ancestral structures of the brain, mainly concerned with instinctive and
emotional behaviour, and the neocortex which endowed man with language,
logic and symbolic thought. MacLean has summed up the resulting state
of affairs in a technical paper, but in an unusually picturesque way:
Man finds himself in the predicament that Nature has endowed him
    essentially with three brains which, despite great differences
    in structure, must function together and communicate with one
    another. The oldest of these brains is basically reptilian. The
    second has been inherited from the lower mammals, and the third is
    a late mammalian development, which . . . has made man peculiarly
    man. Speaking allegorically of these three brains within a brain,
    we might imagine that when the psychiatrist bids the patient to lie
    on the couch, he is asking him to stretch out alongside a horse and
    a crocodile. [4]

If we substitute for the individual patient mankind at large, and for
the psychiatrist's couch the stage of history, we get a grotesque,
but essentially truthful picture of the human condition.

In a more recent series of lectures on neurophysiology, MacLean offered
another metaphor:
In the popular language of today, these three brains might be
    thought of as biological computers, each with its own peculiar form
    of subjectivity and its own intelligence, its own sense of time and
    space and its own memory, motor and other functions . . . [5]

The 'reptilian' and 'paleo-mammalian' brains together form the so-called
limbic system which, for the sake of simplicity, we may call the 'old brain',
as opposed to the neocortex, the specifically human 'thinking cap'. But while
the antediluvian structures at the very core of our brain, which control
instincts, passions and biological drives, have been hardly touched by
the nimble fingers of evolution, the neocortex of the hominids expanded
in the last half a million years at an explosive speed which is without
precedent in the history of evolution -- so much so that some anatomists
compared it to a tumorous growth.

This brain explosion in the second half of the Pleistocene seems to have
followed the type of exponential curve which has recently become so familiar
to us -- population explosion, information explosion, etc. -- and there
may be more than a superficial analogy here, as all these curves reflect
the phenomenon of the acceleration of history in various domains. But
explosions do not produce harmonious results. The result in this case
seems to have been that the rapidly developing thinking cap, which endowed
man with his reasoning powers, did not become properly integrated and
coordinated with the ancient emotion-bound structures on which it was
superimposed with