The ancient origins of consciousness

My dissertation adviser has asked me to cowrite a book review with him on Feinberg and Mallatt's new book, The Ancient Evolutionary Origins of Consciousness. So here are a few preliminary thoughts.

The book tries to shed light on some of the more puzzling features of consciousness, and in particular bridge the infamous explanatory gap, through an investigation of its evolutionary origins. While I am not convinced that it makes much progress in bridging the explanatory gap, it does advance a number interesting and, from my perspective, well-defended hypotheses on the evolutionary origins of and neurological basis of consciousness.  A central point of the the book is that the origins of consciousness, in particular sensory consciousness (aka phenomenal consciousness), began much further back than most scientists currently believe. Feinberg and Mallatt estimate that the first conscious organisms appeared between 560 and 520 mya with the first vertebrates during the Cambrian explosion. They also defend a number of interesting claims about what sort of neuronal complexity must exist to support different kinds of consciousness. They suggest that there must exist at least three levels of neuronal processing to support sensory consciousness, they argue that sensory consciousness consciousness does not depend on the corticothalmic systemthe area of the brain to which the emergence of sensory consciousness was traditionally attributedand they reject the view that affective consciousness (evaluative feelings) depends on the cerebral cortex. As a philosopher interested in the evolutionary history of consciousness, I found the story they tell compelling and richly informative.

Feinberg and Mallatt introduce a list of criteria for singling out consciousness, similar in many ways to other criterial definitions on offer. But unlike other definitions, they place special emphasis on the presence of automatic, fast-acting reflexes and their relationship to multi-layer, nested neural hierarchies that produce isomorphic neural maps using information carried by the reflexes. Throughout the book they try to show, persuasively as far as I can tell, that the early vertebrates satisfy all their criteria (and perhaps some non-vertebrates). The cliffnotes version: the first sensory improvements that evolved at the beginning of the Cambrian explosion triggered an arms race between arthropod predators and vetebrate prey, which led, in turn, to much more advanced sensory modalities (especially in vision), multisensory processing, neural hierarchies, and finally mental imaging--the sort of materials that appear in their criterial definition of consciousness. Specifically, they estimate that the first conscious vertebrates appeared between 560 to 520 mya when the first high resolution eyes and mental imaging evolved. They also argue that primitive interoceptive and affective consciousness were already present among early vertebrates.

On a more philosophical note, the book promises to show that several of the most difficult explanatory hurdles posed by phenomenal consciousness can be overcome by investigating its evolutionary origins and neurological basis. In particular, Feinberg and Mallatt set out to explain four feature of consciousness that philosophy and science have so far struggled to account for: referral (or aboutness), mental unity, qualia, and mental causation. They argue that these features can be explained by their neurobiological naturalistic approach, an extension of Searle's biological naturalism. The basic idea is that we can explain the puzzling features of consciousness entirely in terms of the neurobiological features of nervous systems. The details of their proposal are not discussed in a serious way until the last few sections of the last chapter of the book. Much of the discussion there is simply a re-iteration of the criterial definition given earlier in the book and doesn't seem to draw in a significant way from the evolutionary story that they develop in the previous chapters. One gets the sense that there are really two projects here, one about evolutionary history of consciousness and one about the explanatory gap, and it isn't obvious that they fit together or usefully inform one another.

The discussion in the last chapter draws heavily from Feinberg's recent article, "Neuroontology, neurobiological naturalism, and consciousness: A challenge to scientific reduction and a solution." Like Searle, Feinberg holds that consciousness is "emergent" and "irreducible," but only in a very weak sense. Consciousness is irreducible because it isn't a feature of any of the individual elements that makeup nervous systems, and it is emergent because it only manifests as is a higher-level relational feature of whole nervous systems. Their proposals are as follows:

  1. Referral: an embodied process of nervous systems that emerges out of the relationship between fast automatic reflexes and functionally nested, multi-layer neural hierarchies that produce isomorphic maps out of information carried by the reflexes.
  2. Mental Unity: sensory information carried by automatic reflexes is unified by nested, multi-layer neural hierarchies.
  3. Qualia: "the result of a unique, mulitfactorial neurobiological substrate and recursive interaction within and between higher and lower neurohierarchical levels."
  4. Mental Causation: mental phenomena are identical to processes in the nervous system which have causal efficacy.

Unfortunately, Feinberg and Mallatt say so little about what they take to be in need of explanation that it is difficult to assess whether or not their theory does the job. The philosophical problems posed by these features are, needless to say, complex, and there is significant disagreement about what the exactly the problems are.  While their discussion of neural hierarchies offers some interesting insight into referral, mental unity, and perhaps mental causation, it is not immediately clear what their contributions amount to. Further philosophical work remains to be done.

Philosophers will be especially disappointed by Feinberg and Mallatt's discussion of qualia. This is, perhaps, not surprising, given that explaining qualia is standardly regarded as the really "hard" problem of consciousness. But since one of the main goals of the book is to bridge the explanatory gap, it is a bit of a disappointment. The basic problem is that they offer virtually no explanation for why particular experiences are accompanied by particular qualia--why, for example, the experience of seeing something red is accompanied by phenomenal redness and not, say, phenomenal blueness. To address this issue, Feinberg and Mallatt argue as follows:

We reply that our integrated approach that combines the neurobiological, neuroevolutionary, and neurophilosophical domains is necessary to answer this seemingly impossible question. If we ask you: "Why does red subjective feel 'red,' and 'hurt?" what would you say? First, you could argue that we know that the neurobiology of color processing and pain processing are quite different, so they shouldn't feel the same (a neurobiological answer). Second, you could say that the distinction between the feeling of red and pain evolved because there is strong adaptive value in a response to harm that differs from a response to color (a neuroevolutionary answer). 

Whatever the virtues of this reply, it offers no new insight into the debates surrounding qualia, and it shows little awareness of the details that make the explanatory gap so difficult to bridge. On the assumption that qualia exist, there is nothing terribly mysterious about why pain sensations and blue sensations should illicit different qualia. The really mysterious questions are why they should elicit the specific qualia that they do, and why they elicit any qualia at all. As Chalmers point out, there seems to be nothing incoherent about the idea of creatures that lacks phenomenal consciousness and yet are physically and psychofunctionally just like us. This is the really "hard" problem of consciousness, and it is a problem that Feinberg and Mallatt simply do not address.

None of this is to suggest that the "hard" problem of consciousness is well-formed or that scientists should take it seriously. Perhaps the very notion of qualia is incoherent. The point is simply that Feinberg and Mallatt have not addressed the problem on its own terms.