Emergence
18-Dec-2013: Minor update.

Consciousness is sometimes said to be an emergent property of the brain, usually posited as being a result of its complexity.

The meaning of the term "emergence" is intuitively obvious but difficult to define precisely. According to the Stanford Encyclopaedia of Philosophy:

"Emergence is a notorious philosophical term of art. A variety of theorists have appropriated it for their purposes ever since George Henry Lewes gave it a philosophical sense in his 1875 Problems of Life and Mind. We might roughly characterize the shared meaning thus: emergent entities (properties or substances) ‘arise’ out of more fundamental entities and yet are ‘novel’ or ‘irreducible’ with respect to them. (For example, it is sometimes said that consciousness is an emergent property of the brain.)"
(O'Connor and Wong, 2012)
David J Chalmers in Chalmers 2006 divides emergence into two types, strong and weak. The distinction does not materially alter the issues.

The concept of emergent phenomena is often used interchangeably with the concept of epiphenomenalism. Although this is valid in many cases (think of the emergent epiphenomena in Conway's Life), the two are not strictly equivalent. It's possible to theorise emergent phenomena that are not epiphenomenal and vice versa. So emergent consciousness may or may not be impotent. However all examples of emergence we have from other fields lack downward causation and are indeed impotent epiphenomena. It would seem to require unjustified special pleading for consciousness to be an exception.

There is a question mark over the ability of emergence to fully account for our experiences of phenomenal consciousness and free will. Even if we put those aside and assume that emergence is a valid model for consciousness in principle, practical issues still remain.

If consciousness is indeed an emergent phenomenon - epiphenomenal or otherwise - then we can ask what causes it to emerge. Why does consciousness emerge from a human brain and not from a haggis stew? Is there something special about the physical material - the meat - that makes up our brain?

Complexity

The most widespread view seems to be that it is not the physical matter of the brain per se that causes consciousness to emerge. Rather it is the complex arrangement of neurons, synapses and their sensory input that produces consciousness. This seems initially appealing - the human brain is an extremely complex structure with billions of neurons and even more connecting synapses.

Unfortunately we are still left with the question: "What's so special about neurons and synapses?". Basically they're simple biological components which pass electrical impulses. Why should consciousness arise out of them and not out of the mix of proteins that make up haggis? There is a danger that in attempting to avoid giving any privileged status to "consciousness" the emergence hypothesis has unwittingly just passed that privileged status on to grey matter.

An answer to this is to say that it is not the physical units that matter but the link between them and the complex structure they form. That argument has always been at risk from observations of people with major brain injury who are still (we believe) conscious. In addition there are people who suffer from conditions such as dyslexia, autism and severe head injury - yet remain conscious despite physical or organisational brain damages. If consciousness is a result of specific meta-level organisation, how can it survive such systemic damage? Only if the damaged parts of the brain are not essential for consciousness. The centre of emergence is thus slowly forced to retreat - possibly all the way back to Descartes' pineal gland!

The complexity argument has also become less compelling since the rise of the internet. The world wide web today contains many more many pages and links than the human brain has neurons and synapses. Yet outside of science fiction very few people would seriously describe the internet as conscious.

Colin McGinn says the following about the complexity argument:

"Some people like to harp on the complexity of the brain, as if this gave a clue to its mental productivity. But sheer complexity is irrelevant: merely adding more neurons with more synaptic connections doesn't explain our problem a bit. The problem is how any collection of cells, no matter how large and intricately related, could generate consciousness. The trouble is that neural complexity is the wrong kind of thing to explain consciousness; it is merely a matter of how many cells a given cell can causally interact with. If our kidneys had as many cells as our brains, that would not make them conscious. Nor is a galaxy conscious just because it has a tremendous number of interacting parts. If complexity is to play a role in generating consciousness, then we need to be told what kind of complexity is involved."
(McGinn 1999, emphasis original)
So complexity alone is not enough and we've gone full circle: consciousness arises not just from complexity but from complexity of something specific. Maybe it requires a specific type of organic material or specific electrical interaction of synapses and neurons. This conclusion represents a retreat from the fundamental idea of consciousness as an emergent property of a complex system. We must also give some (undetermined) aspect of the human brain a privileged status not available to other meat. That may well be true - but it's no longer pure emergence.

Can the special status of the human brain in emergence be defended by evolution? Perhaps millions of years of evolutionary pressure have slowly nudged the structure of the human brain into a specific arrangement from which consciousness emerges? That might answer the "why" of emergence but still says nothing about the "how". And if true then it rules out epiphenomenalism; if consciousness is impotent then it cannot be affected by evolutionary pressures.

If we do accept consciousness is an emergent phenomenon resulting from the complexity of the human brain then this has a number of unpleasant ethical implications over and above those generated by impotent consciousness. The existence of these in no way undermines the emergence hypothesis - just because something is unpleasant doesn't mean it isn't true - however these implications need to be faced up to and not brushed under the academic carpet.

Consciousness as an emergent phenomenon remains intuitively appealing, however the position is becoming more difficult for me to support. Unless we can be more specific about how and from what consciousness emerges then emergence remains little more than hand waving which does nothing to enhance our understanding.

References:
Chalmers, David J. Strong and Weak Emergence in "The Re-Emergence of Emergence" (OUP)
 McGinn, Colin. 1999. The Mysterious Flame
 O'Connor, Timothy and Wong, Hong Yu. 2012. Emergent Properties, The Stanford Encyclopedia of Philosophy (Spring 2012 Edition)