Let's start off with a longish quote from the neuroscientist, writer and broadcaster Susan Greenfield:
“The idea [of a conscious robot] is ridiculous. Consciousness entails an interaction between the brain and the body, trafficking a myriad of chemicals between the two. To reproduce that, you would have to build a body with a whole range of chemicals, and the three-dimensionality of the brain would have to be preserved to the very last connection.”
Susan Greenfield puts what can be called the case for biologism when it comes to consciousness. The way Greenfield expresses this position seems to make her an even stronger proponent of biologism than John Searle (who'll be discussed in a moment). Her argument appears to be excruciatingly simple. It's this:
In order to create artificial consciousness, we would need to build a biological brain and a biological body.
Or less extremely:
In order to create artificial consciousness, we would need to replicate a biological brain and a biological body.
Or even more simply:
In order to replicate x, we would need to replicate everything of x (which has y) – down to its material constitution.
You could ask what would be the point of replicating biological brains and biological bodies when we already have them. (Though the replication of brains and bodies - regardless of consciousness - would be an incredible thing.) This would be equivalent to a scientific model that literally replicated every aspect of that which it is modelling.
Another way of putting this is to say that Susan Greenfield's position is the exact opposite of functionalism. That is, it's not functions (or computations, algorithms, etc.) which matter to consciousness: it's the material constitution (or "substrate") which underpins it. Indeed isn't that why Greenfield talks in terms of “trafficking a myriad of chemicals between” the brain and body and then goes on to say that
“to build a body with a whole range of chemicals, and the three-dimensionality of the brain would have to be preserved to the very last connection”?
Here Greenfield goes beyond material constitution (which would include biochemicals) to stressing the “three-dimensionality of the brain”. Thus we've moved beyond material constitution to the shape/dimensionality of the brain. (In any case, three-dimensionality - at least in the abstract - would be easy to replicate.)
Again it would seem that the replication of consciousness would require the replication of both the brain and body in their entirety. That would be a pointless act of replication in terms of replicating consciousness. Though in terms of creating artificial-life-with-consciousness it would be earth-shattering.
Despite all that, the Chalmers, Penroses and dualists among us may still ask Susan Greenfield and others the following question:
What if we carried out this act of perfect replication (of both brains and bodies) and it still turned out that the replica didn't have consciousness?
Even though that's a subject for another day, I suspect that some philosophers would discount this possibility in an a priori manner.
Many philosophers and scientists have called John Searle a dualist. He, in return, says that those who stress function and ignore biology are effectively creating a non-material Cartesian reality populated with functions or computations (rather than with Cartesian “ideas” or “thoughts”). Searle himself writes:
“I believe we are now at a point where we can address this problem as a biological problem [of consciousness] like any other. For decades research has been impeded by two mistaken views: first, that consciousness is just a special sort of computer program, a special software in the hardware of the brain; and second that consciousness was just a matter of information processing. The right sort of information processing -- or on some views any sort of information processing --- would be sufficient to guarantee consciousness..... it is important to remind ourselves how profoundly anti-biological these views are. On these views brains do not really matter. We just happen to be implemented in brains, but any hardware that could carry the program or process the information would do just as well. I believe, on the contrary, that understanding the nature of consciousness crucially requires understanding how brain processes cause and realize consciousness.. ”
“Perhaps when we understand how brains do that, we can build conscious artifacts using some nonbiological materials that duplicate, and not merely simulate, the causal powers that brains have. But first we need to understand how brains do it.”
It can be said that there can be an artificial mind without having an artificial (human) brain. However, isn't that precisely the claim that's being disputed?
To John Searle, it's all about what he calls “causal powers".
This refers to the ostensible fact that a certain level of complexity is what's required to bring about those causal powers which are necessary for intentionality, mind and consciousness. Despite that, Searle never never says (as far as I know) that biological brains are the only things capable - in principle - of bringing about consciousness and intentionality (therefore semantics, in Searle-speak). He only says that biological brains are the only things known which are complex enough to do so.
So it really is all about the biological and physical complexity of brains and therefore their causal powers.
Searle's basic position (like Greenfield's) on this is that if computationalists or functionalists, for example, ignore the physical biology of brains and exclusively focus on syntax, computations or functions (the form/role rather than the physical embodiment), then that will surely lead to a kind of dualism. What Searle means by this is that there's a radical disjunction created here between the actual physical reality of the brain and how these philosophers explain - or account for - intentionality, mind and consciousness.
Again, Searle doesn't believe that only brains can give rise to minds. Searle's position is that only brains do give rise to minds. He's emphasising an empirical fact; though he's not denying the logical and metaphysical possibility that other things can bring forth minds.
Gerald Edelman also holds the position that the mind
“can only be understood from a biological standpoint, not through physics or computer science or other approaches that ignore the structure of the brain”.
Then Edelman - in order to demonstrate his point - puts the seemingly extreme position of “functionalists” (such as Marvin Minsky) who “say they can build an intelligent being without paying attention to anatomy”. So if one says that biology matters, one's also saying that functions aren't everything (though not that functions are nothing).
Finally, according to Francis Crick, psychologists (as well as philosophers)
“have treated the brain as a black box, which can be understood in terms merely of inputs and outputs rather than of internal mechanisms”.
Thus, to Greenfield, Searle, Edelman and Crick, consciousness really is all about biological brains.
Crick, Francis. (1996) quoted in The End of Science, by John Horgan
Edelman, Gerald. (1996) quoted in The End of Science, by John Horgan
Greenfield, Susan. (1999) quoted in Predictions: 30 Great Minds on the Future (edited by Sian Griffiths).
Searle, John. (1999) 'Consciousness'