Chapter
Ten
Evolution and animal minds
what to seek out, and when to dive for safety. We have nothing comparable to
help us imagine it. The insects have compound eyes quite unlike our image-form-
ing eyes, and many of the animals have chemical senses far more sensitive than
our feeble senses of smell and taste.
The frog is particularly interesting. Frogs have eyes with lenses and retinas some-
what like ours, sending signals along the optic nerve to the optic tectum in the
brain. It is tempting to imagine that a picture of the frog’s world is somehow
constructed in its brain, but this is not so. The frog’s eye tells the frog’s brain just
what it needs to know and no more. It tells it about stationary and moving edges,
changes in overall illumination, and bugs. The ‘bug detectors’ respond specifically
to small moving objects, not to large moving ones or small still ones, and direct
the frog’s tongue to catch flies. An extraordinary consequence of the way this sys-
tem works is that a frog can literally starve to death surrounded by freshly killed
flies. If the fly does not move, the frog does not see it.
We can learn much from thinking about this frog. We might be inclined to think
that the child gazing into the pond really does have a picture of the world in her
head – a full, rich, and detailed picture of the scene – and that by comparison the
frog’s vision is simply stupid. But think again. The discoveries of change blindness
and inattentional blindness, and of the different roles of the dorsal and ventral
streams in the visual system (Chapter 6), suggest that we may be much more like
the frog than we care to admit. Evolution has designed us to detect only selected
aspects of the world around us, often only when we need them for action. Just
like the frog, we are quite unaware of everything else – yet we feel no gaps.
We may think that the child must be more conscious than the frog, and the frog
more conscious than the fly, but why? While many authors make bold assertions
about animal consciousness, it is not clear how these can be tested or what they
mean. British pharmacologist Susan Greenfield proposes that ‘consciousness
increases with brain size across the animal kingdom’ (2000, p. 180). But if she
is right, then sperm whales, African elephants and dusky dolphins are all more
conscious than you are, and Great Danes and Labradors are more conscious than
Jack Russells and Pekinese. Searle claims that ‘Humans and higher animals are
obviously conscious, but we do not know how far down the phylogenetic scale
consciousness extends’ (1997, p. 5). But this is not ‘obvious’, and there is no single
phylogenetic scale, or linear sequence, along which animals can be graded from
‘higher’ to ‘lower’. As we have seen, evolution has produced not a line but a very
bushy bush.PHYSICAL AND BEHAVIOURAL CRITERIA
Ideally we need to find some clear criteria for consciousness that we can
apply to other animals. One way is to look for anatomical or other physical
features – not just brain size but aspects of brain organisation and function
that we think are indicators of consciousness. We might argue that fish can-
not be conscious because human consciousness relies on signal amplification
and global integration, and fish lack the neural architecture that makes these
possible, in particular the strongly interconnected feedforward and feedback
circuitry that allows for neural signals to be both differentiated and integrated
(Key, 2016).‘He [the frog] will starve
to death surrounded by
food if it is not moving’(Lettvin et al., 1968, p. 1940)that consciousness is a fundamental biological adaptation and that the
known anatomical and physiological bases of consciousness are phylo-
genetically ancient, going back at least to the early mammals. We read-
ily attribute consciousness to other people on the basis of behavioural
and brain evidence, so we should not deny it to other mammals. Psy-
chiatrist Todd Feinberg and biologist Jon Mallatt (2016) go even further
back, to the time of the Cambrian explosion more than five hundred
million years ago. Unconscious reflexes gradually evolved into brains
with ever increasing levels of consciousness leading eventually to uni-
fied inner worlds of subjective experience. So in their view, every fish,
reptile, amphibian, and insect is conscious, and possibly cephalopods
like our octopus, too.
Others distinguish between primary consciousness, or sensory con-
sciousness – the ability to integrate perceptual and motor events with
memory to create awareness of the present world around you – and
secondary or higher-order consciousness, which involves conscious-
ness of being conscious, and the ability to connect the present to the
past and future (G. Edelman, 2003). Distinctions like these may mean that con-
sciousness is basically a binary, on/off phenomenon, or they may allow for certain
animals to be partially or incompletely conscious (Allen and Trestman, 2016). We
should not, in any case, assume that there is just one kind of consciousness. Nor
should we assume that, if there are multiple kinds or levels of consciousness, the
human kind is the standard by which all the others should be measured.‘Humans and higher
animals are obviously
conscious’(Searle, 1997, p. 5)‘affective, interoceptive,
and exteroceptive
consciousness all existed
in the first vertebrates of
the Cambrian explosion’
(Feinberg and Mallatt, 2016,
p. xvii)