- seCtIon FoUR: eVoLUtIon
Computational neuroscientist Anil Seth and his colleagues (2005) argue that
among the basic brain facts are that consciousness ‘involves widespread, rela-
tively fast, low-amplitude interactions in the thalamocortical core of the brain,
driven by current tasks and conditions’ (p. 119). The lower brainstem is involved
in maintaining the state of consciousness, while the thalamocortical complex
sustains conscious contents. So, finding these features in the brains of other spe-
cies should show us that they are conscious. Seth concludes that most mammals
share these structures and therefore should be considered conscious.
What about those many creatures that have no cortex and therefore no thalam-
ocortical connections, from brainless molluscs, through tiny-brained worms and
insects, to fish and reptiles? Bjorn Merker (2007) argues that all vertebrate brains
share a centralised functional design with an upper brainstem system organised
for conscious function. In simple brains, this system is involved in action control;
in more complex ones, it takes on the task of integrating the massively parallel
processing of the higher brain areas into the limited-capacity serial processing
required for coherent behaviour. On this view, even simple-brained creatures
with no cortex at all can be conscious.
A common theme here is that the brainstem controls states of consciousness
and the sleep-waking cycle, while the forebrain sustains complex contents of
consciousness. All mammals, and most other animals (including many fish and
reptiles, some insects, and even the simple roundworm C. elegans), alternate
between waking and sleeping states, or at least have strong circadian rhythms
of activity and responsiveness. So, in the sense of being awake, they are con-
scious, but is there something it’s like to be them: are they having conscious
perceptions, thoughts, feelings? When it comes to conscious ‘contents’, we
face again the difficulties involved in pinning down the NCCs and the prob-
lems we encountered with the whole notion of the ‘contents of consciousness’
(Chapter 4). These problems are even more acute when asking about the NCCs
of non-human animals. Here, it is even more difficult to distinguish between
prerequisites, substrates, and consequences of conscious experience – and, of
course, to determine what experiences count as conscious in the first place
(Boly et al., 2013).
If we had a complete theory that specified the neural basis of consciousness, we
could use it to determine the status of animals’ minds. But we do not. As Seth and
colleagues (2005) point out, neural theories of consciousness are new, and the list
of criteria may need to change. And until then, we should not just guess which
features are needed for consciousness and go looking for them. This is what Fein-
berg and Mallatt (2016) appear to do when they specify that the ‘defining features
of consciousness’ include non-nested and nested hierarchical functions, isomor-
phic representations, and mental images, and that sensory hierarchies require
four or more levels to be conscious. Seeking these in other species is how they
arrived at their conclusion that ‘the transition from non-conscious to conscious’
happened between 560 and 520 million years ago.
The other main approach is to look at behavioural indicators. For example, a
mobile lifestyle (octopuses, not clams; animals, not plants) might drive the need
for general-purpose perception, flexible planning, and precisely controlled
action, and these might be conducive to developing subjectivity (Klein and Bar-
ron, 2016). We might also ask whether organisms capable of particular types of
‘What then do noxious
stimuli feel like to a
fish? The evidence
best supports the idea
that they don’t feel like
anything to a fish’
(Key, 2016, p. 17)
‘Consciousness probably
evolved first in fishes’
(Balcombe, 2016, p. 85)
‘we seek the minimum
number of levels a
sensory hierarchy
can have to produce
consciousness’
(Feinberg and Mallatt, 2016,
p. 98)