Of all the different ways that the bodies of animals are arranged, which ones contain structures and arrangements that give rise to consciousness?... The word “sentience” is sometimes used instead of consciousness. Sentience refers to the ability to have positive and negative experiences caused by external affectations to our body or to sensations within our body. The difference in meaning between sentience and consciousness is slight. All sentient beings are conscious beings. Though a conscious being may not be sentient if, through some damage, she has become unable to receive any sensation of her body or of the external world and can only have experiences of her own thoughts.
Caterpillar...
To be conscious is to be able to have some kind of subjective
experience or awareness of something.1 We can only experience
something if we are conscious, and if we are conscious it means we
can have experiences. Conscious beings can experience something
external in the environment or something internal to the body. It
can be the experience of a feeling or of a thought of any type. An
experience is positive when the subject enjoys it, is satisfied with
it, or is pleased by it. It is negative when it involves some form
of suffering. To suffer is to have a negative experience.
All emotions and feelings that we have are experiences, and we can
also have experiences that are caused only by our thoughts. We can
have these experiences insofar as we are conscious; indeed, the fact
itself of having experiences is, as noted above, to be conscious.
The word “sentience” is sometimes used instead of consciousness.
Sentience refers to the ability to have positive and negative
experiences caused by external affectations to our body or to
sensations within our body. The difference in meaning between
sentience and consciousness is slight. All sentient beings are
conscious beings. Though a conscious being may not be sentient if,
through some damage, she has become unable to receive any sensation
of her body or of the external world and can only have experiences
of her own thoughts.
When a being has an experience, there exists in that being what we
can call a subject, that is, a “someone” who is having the
experience, an “I” who is conscious. The word subjective, which
refers to inner, or personal, experiences, refers to this subject. A
subject is a someone, one who experiences their world, as an animal
does. An object is a thing that does not experience its world. A
chicken is a subject of experience, whereas a rock is not. If you
pet a chicken she will feel pleasure. If you pet a rock, there is no
one there to feel anything.
The question we have to answer is: what sorts of beings are sentient
(and, therefore, conscious)? Or, put another way, what kind of
physical structure and arrangement of nerve cells does a being have
to have so that it isn’t merely a collection of cells, but a
conscious being?2
What is the problem of consciousness?
The problem of consciousness can be formulated as follows: how is it
that, from a purely material basis (a brain or a centralized nervous
system), consciousness emerges?3 This is what the problem of
consciousness really boils down to. Answering this requires
answering the question, what structures must be present in an
organism and how would they function for consciousness to be
possible? In other words, of all the different ways that the bodies
of animals are arranged, which ones contain structures and
arrangements that give rise to consciousness? There is no reason to
suppose that only a human-like central nervous system will give rise
to consciousness, and a great deal of evidence that very different
types of animals are conscious. An example is bird brains, which
have many structural similarities to mammalian brains, but different
arrangements of neurons. Yet their brain circuits seem to be wired
in a different way that creates a similar effect in terms of
consciousness and cognition. An octopus is an invertebrate with a
very different type of nervous system. But an octopus exhibits
behavior and responds to her environment like a conscious being.
Why is it that only beings with a centralized nervous system
are sentient?
We don’t yet know what causes consciousness to arise. And until we
know this, we can’t know which beings will be sentient. But we do
know that, in the absence of at least a centralized nervous system,
consciousness will not arise in an animal. By this, we must
understand a nervous system that not only transmits information, but
has also some brain or ganglia that processes it. We know that
beings lacking a centralized nervous system cannot be conscious.
Non-centralized nervous systems do transmit information about damage
in some part of the organism, but this information does not result
in a conscious experience because there is no bodily structure in
which a sufficiently large aggregate of nerve cells interact to
process an experience, as opposed to merely transmitting the
information. It is the processing of information that produces the
experience. Processing or computing information is not merely an
indication of consciousness. Consciousness seems to be impossible if
no processing occurs.
Reflex arcs: How a nervous system operates without giving
rise to an experience
In our bodies, if our knee is lightly tapped, our leg moves
automatically (with no intention on our part) and independently of
the experience of the tap that we sense. The information that
originates in our knee, with the tap, splits up and moves through
two separate pathways: one path goes to our brain through the spinal
cord, where it is processed to produce the corresponding experience;
the other path involves a different circuit, going through the
spinal cord to the muscles that operate the leg, without ever
reaching the brain. In the second path, the information takes a much
shorter direct route to enable our body to react quickly to the
stimulus (‘reflex arc’). There is a good reason why this dual
mechanism exists. There are cases where some part of the body will
be endangered by a slow reaction to an external threat. If we had to
think about moving because of pain, rather than responding
automatically, we might not act quickly enough to avoid harm.
What is relevant here is that the information transmitted through
this ‘reflex arc’ is never experienced because it is never processed
by a central nervous system. The non-centralized nervous systems of
some animals operate just as reflex arcs do. Information is
transmitted from the cells receiving certain stimuli to other cells
which must be activated, without any involvement of subjective
experience. In these cases, there is a merely mechanical
transmission of information. Such reactions are not an indication of
sentience.
For this reason, we can rule out the hypothesis that beings without
a centralized nervous system are sentient, just as we can for
organisms lacking a nervous system altogether (see
Which beings are not conscious).
What is known about the emergence of consciousness?
How do the structures and arrangements of different centralized
nervous systems operate to give rise to consciousness? We don’t
know.
Currently, researchers are trying to identify the neural correlates
of consciousness in humans. The neural correlates of consciousness
are the “neural events”, i.e., the ways that sets of neurons work
and operate when a given mental operation occurs.4 In connection
with this, researchers are studying human subjects who have suffered
brain lesions and who have, as a consequence, lost some aspects of
consciousness. These studies are in their infancy and it will take a
very long time before we have a solid understanding of the neural
correlates of consciousness.
Knowing what operations take place in a nervous system when some
experience occurs does not explain how those operations create the
experience. And the neural correlates of a certain type of
experience might be different in different types of animals, like
birds, cetaceans and cephalopods. We just don’t know. Such early
research can provide only limited knowledge and while the problem of
what consciousness is and how it arises remains unsolved,
speculations about how centralized nervous systems produce
experiences will remain open to revision.
Due to the difficulty of solving the problem of consciousness, those
who study it agree that it is unlikely that it will be solved in the
near future. Given what we know today, we can only make rough
estimates about which beings are more or less likely to be sentient
and we can confidently assert that certain beings are not sentient.
Given current information, it is impossible to know with certainty
which beings with centralized nervous systems are conscious. We know
that without such a system there cannot be consciousness, but we do
not know what degree of complexity such a system must possess for
consciousness to emerge. We cannot know exactly which beings can
have experiences until we know exactly what physical basis is
necessary for consciousness and therefore experiences. And we cannot
answer this question until we solve the problem of how consciousness
arises.
The significance of having experiences that are positive or
negative
In order to determine which beings to give moral consideration to,
we must consider that beings who have experiences as a result of the
evolutionary process can have both positive and negative
experiences.5 If there were beings who had either positive or
negative experiences only, these beings would also deserve moral
consideration.
There could also be entities that have experiences that are neither
positive nor negative. There is a difference between the capacity to
have experiences in general and the capacity to have positive or
negative experiences specifically. It may be possible to create a
computer that can have experiences yet is indifferent to those
experiences. Its experiences would be neither positive nor negative.
The computer wouldn’t care whether it has them or not. Such a
computer would also be indifferent towards its own continued
existence. Because it would lack positive and negative experiences
altogether, the computer wouldn’t care how we treated it. Regardless
of what we did to the computer, it would be impossible for us to
harm or help it. If it were in any way pleased about the prospect of
continuing to exist, or upset at the thought of its own death, the
computer would then count as having positive or negative
experiences, and would have to be considered a different kind of
entity, one that is sentient.
We know that sentient animals, human and nonhuman, have experiences
that are positive or negative. Since the problem of consciousness
will likely remain unsolved for many decades, we should act on the
assumption that any animal with a centralized nervous system may be
sentient. We should consider the likelihood that they are sentient,
and that we can affect them through our actions, and so we should
give them moral consideration.
Further readings
Barron, A. B. & Klein, C. (1996) “What insects can tell us about the
origins of consciousness”, PNAS, 113, pp. 4900-4908 [accessed on 24
December 2016].
Chalmers, D. J. (2003) “Consciousness and its place in nature”, in
Stich, S. P. & Warfield, T. A. (eds.) Blackwell guide to philosophy
of mind, Oxford: Blackwell, pp. 102-142.
Feinberg, T. E. & Mallatt, J. M. (2016) The ancient origins of
consciousness: How the brain created experience, Oxford: Oxford
University Press.
Gennaro, R. J. (2005) “Consciousness”, Internet Encyclopedia of
Philosophy [accessed on 13 November 2013].
Godfrey-Smith, P. (2016) Other minds: The octopus, the sea, and the
deep origins of consciousness, New York: Farrar, Straus and Giroux.
Gray, R. (2003) “Recent work on consciousness”, International
Journal of Philosophical Studies, 11, pp. 101-107.
Gregory, R. L. (ed.) (2001) Oxford companion to the mind, Oxford:
Oxford University Press.
Honderich, T. (2004) On consciousness, Oxford: Oxford University
Press.
Hurley, S. L. (1998) Consciousness in action, Oxford: Oxford
University Press.
Ito, M.; Miyashita, Y. & Rolls, E. T. (1997) Cognition, computation,
and consciousness, Oxford: Oxford University Press.
Jackendoff, R. S. (1987) Consciousness and the computational mind,
Cambridge: MIT Press.
Kriegel, U. (2006) “Theories of consciousness”, Philosophy Compass,
1, pp. 58-64.
Lormand, E. (1996) “Consciousness”, Routledge Encyclopedia of
Philosophy [accessed on 26 November 2013].
Lloyd, D. (2004) Radiant cool: A novel theory of consciousness,
Cambridge: MIT Press.
Lycan, W. G. (1987) Consciousness, Cambridge: MIT Press.
Lycan, W. G. (1996) Consciousness and experience, Cambridge: MIT
Press.
McGinn, C. (2004) Consciousness and its objects, Oxford: Oxford
University Press.
Metzinger, T. (1985) “Introduction: The problem of consciousness”,
in Metzinger, T. (ed.) Conscious experience, Exeter: Imprint
Academic, pp. 3-37.
Minsky, M. (2006) The emotion machine: Commonsense thinking,
artificial intelligence, and the future of the human mind machine,
New York: Simon & Schuster.
Nadel, L. (ed.) (2003) Encyclopedia of cognitive science, London:
Nature Publishing Group.
Nelkin, N. (1996) Consciousness and the origins of thought, Oxford:
Oxford University Press.
O’Shaughnessy, B. (2000) Consciousness and the World, Oxford: Oxford
University Press.
Notes
1 Nagel, T. (1974) “What is it like to be a bat?”, Philosophical
Review, 83, pp. 435-450.
2 It seems perfectly possible that a structure different from the
neural wiring of sentient animals would be able to perform analogous
functions. Therefore, it is in principle possible that there could
be minds that are not organic, although in our world, currently at
least, only animals with centralized nervous systems are conscious.
3 Chalmers, D. J. (1996) The conscious mind: In search of a
fundamental theory, Oxford: Oxford University Press.
4 Rees, G.; Kreiman, G. & Koch, C. (2002) “Neural correlates of
consciousness in humans”, Nature Reviews Neuroscience, 3, pp.
261-270. Block, N. (2005) “Two neural correlates of consciousness”,
Trends in Cognitive Sciences, 9, pp. 46-52.
5 Griffin, D. R. (1981) The question of animal awareness:
Evolutionary continuity of mental experience, New York: Rockefeller
University Press. Cabanac, M.; Cabanac, A. J. & Paren, A. (2009)
“The emergence of consciousness in phylogeny”, Behavioural Brain
Research, 198, pp. 267-272. Grinde, B. (2013) “The evolutionary
rationale for consciousness”, Biological Theory, 7, pp. 227-236. Ng,
Y.-K. (1995) “Towards welfare biology: Evolutionary economics of
animal consciousness and suffering”, Biology and Philosophy, 10, pp.
255-285.