Since evolution is a physical process, mental states must be as well

The argument

Evolution is an entirely physical process. It operates on physical organisms through physical mechanisms — variation in bodies, differential survival, inheritance — and introduces nothing that is not matter arranged in some new way. Human beings, including whatever it is that does their thinking, are products of that process. It is therefore sensible to conclude that the creation of mental states was itself a purely physical development, since a physical process is not the sort of thing that can deliver a non-physical result. The alternative view faces a problem of distribution. If minds were non-physical additions rather than outcomes of physical organisation, there is no evolutionary point at which their arrival could be located, because evolution is continuous and admits no such threshold. Whatever gradual physical change produced human brains produced animal brains by the same means, and the same reasoning would extend to plant life. Either non-physical minds are far more widely distributed than defenders of that view are willing to allow, or mental states are physical after all. The gestation of a foetus poses the difficulty in sharper form. A foetus grows into a human being through the division and multiplication of billions of tiny physical cells, one step at a time, with nothing but matter entering the process at any stage. At what point in that sequence does the non-physical soul develop? No answer is available that does not look arbitrary: no cell division differs in kind from the one before it, and there is no moment at which the physical account runs out and something else must be invoked. Since both the emergence of the species and the formation of each individual are exhaustively physical, materialism concludes that mental states must be physical as well.

Context

The materialist argument proposes that humans are made out of purely physical matter. There is no non-physical aspect to our being, nor is there a non-physical mind which exerts force over our bodies. Within the neurons and fibres of our brain, we are able to experience everything known as life. Emotions, feelings, and mental states can be reduced to brain activity and the release and production of chemicals. When we say, “I feel pain”, we are essentially saying, “I am experiencing c-fibre stimulation”, in exactly the same way as when we say, “a noise is loud”, we are simply saying, “the airwave signal has a large amplitude”.

Premises

Counter-arguments

The Philosophical Zombie While no philosophers assert that zombies exist, the philosophical zombie has been employed as a thought exercise to refute the claims of materialists. In the nineteenth century, following a cascade of scientific breakthroughs, materialism began to gain favour as an epistemological argument. Thinkers like G.F. Stout and David Chalmers have since challenged the notion of evolution and Darwinism as evidence of materialism's strength. Imagine a zombie world, exactly like this one, with the same physical laws, conditions, and species. Each of us has a zombie twin, with identical physical characteristics, that interacts with the world in the exact same way we do. Except our zombie twin lacks non-physical consciousness. In the zombie world, there are no conscious experiences. Would the zombies act the same way as we do? Would they feel pain? Would they see colour? If they wouldn't, then materialism as a position in the mind-body debate is untenable.

Rejecting the premises

When we think about the colour blue or brain does not go blue. Therefore, mental states are not merely physical states.