Given the evidence for the gradual evolution of the human brain, it also seems
unlikely that consciousness first emerged in the universe, fully formed, in homo
sapiens. As the naturalist Thomas Huxley observed in 1874,
"The doctrine of continuity is too well established for it to be permissible to me to
suppose that any complex natural phenomenon comes into existence suddenly, and
without being preceded by simpler modifications; and very strong arguments would
be needed to prove that such complex phenomena as those of consciousness, first
make their appearance in man.”
Is consciousness confined to complex brains?
One cannot be certain that other animals are conscious - or even that other people are
conscious (the classical problem of “other minds”). However, the balance of evidence
strongl y supports it (Dawkins, 1998, Panksepp, 2007). In cases where other animals
have brain structures that are similar to humans, that support social behaviour that is
similar to humans (agression, sexual activity, pair-bonding and so on), it is difficult to
believe that they experience nothing at all! But if one does not place the
conscious/nonconscious boundary between humans and non-humans where should
one place it?
It might be that consciousness is confined to animals whose brains have achieved
some (unknown) critical mass or critical complexity. The contents of human
consciousness are constructed from different sense modalities, and within a given
sense modality, experiences can be of unlimited variety and be exquisitely detailed.
Where such conscious states are complex, the neural states that support them must
have equivalent complexity. However it does not follow from this that only brains of
similar complexity can support any experience. Complex, highly differentiated brains
are likely to be needed to support complex, highly differentiated experiences. But it
remains possible that relatively simple brains can support relatively simple
experiences.
Given this, it is tempting to search for the conditions that distinguish conscious from
nonconscious processing in our own brains irrespective of complexity—for example
to isolate neural changes produced by simple stimuli just above and below some
threshold of awareness in different sense modalities. This is a sensible strategy that is
widely pursued in psychology and associated brain sciences. In the human case, only
representations at the focus of attention reach consciousness and then only in a
sufficiently aroused state (an awake or dreaming state, but not coma or deep sleep), so
it would be useful to learn what happens to such representations to make them
conscious. Common suggestions are activation of neuronal activity above some
critical threshold (Merickle, 2007), the activation of specific consciousness-bearing
circuitry (Crick & Koch, 2007; Rees & Frith, 2007), “neural binding” produced by
relatively coherent, phase-locked activity of some neural sub-populations relative to
the uncoordinated activity of other populations (Singer, 2007), and a transition from
modular, restricted forms of information processing to widespread information
dissemination throughout the brain (Baars, 2007, Dehaene & Naccache, 2001) .
Even if one of these or some combination of these conditions for consciousness turn
out to be necessary for consciousness in the human mind/brain, we still need to be