When it is stated that sentience has a purpose, this idea is usually explained by indicating that sentience is useful because it motivates doing certain things and avoiding others. In addition, in this explanation, it is usually indicated that sentience motivates but does not force. That is, under this explanation, sentience is not simply the cause and behavior the consequence, but sentience motivates to strive to make the best possible decision, under the threat of pain and the reward of pleasure. According to this explanation, sentient beings would make better decisions and will be selected (“better”, from an evolutionary point of view).
But we can also consider that it is possible that we are sentient robots, but without will, that we simply do what we have been programmed for, even though we have the feeling that we make free decisions, so that sentience really does not play any role in the evolution in form of motivation.
So, is sentience useful or inevitable?
My best intuition is that sentience is probably inevitable when certain conditions are met. So, sentience would be inevitable. Not useful. But let’s assume for a moment that sentience is useful. If sentience were useful, then sentience must incorporate some element that goes beyond classical physics, to be really useful. For example, related to quantum physics or the multiverse.
Why?
Because if sentience had a positive effect (in the form of motivation) on survival, in some way that can be explained by classical chemistry and physics, for example, thinking faster, taking better decisions, or being able to escape running faster than a predator, this behavior, that would be evolutionarily selected, would have to compete with another behavior that would also be evolutionarily selected, which is to do exactly the same, following the laws of chemistry and classical physics, but without the sentience.
I will give an example to try to illustrate all this.
Suppose we have a DNA chain that “reproduces as much as possible” and that follows the laws of classical physics. This chain does not feel.
By the way, when I say that the chain “reproduces as much as possible” I am not assigning agency, but summarizing in that phrase what is happening on a physical level. That chain that “reproduces as much as possible” is simply matter following the laws of physics. The phrase “reproduces as much as possible” is a summary way of describing what is happening.
We also have a second strand of DNA also formed by physical particles and obviously also that “reproduces as much as possible.” However, this DNA chain does feel: it feels pleasure every time it reproduces and frustration if it can not. Which motivates it to reproduce as much as possible.
This second strand of DNA is motivated to reproduce, but in what physical way would it be able to do it better than the chain that does not feel, and therefore is not “motivated”?
Whichever way we imagine that this second chain can do something better than the first chain, if it is following the laws of physics, it is something that chains like the first one could also perform. That is, evolution could always create chains that do not feel, like the first one, and that would have that characteristic of being more efficient, like the second one. Then both types of chain could exist: those that feel and those that do not feel. Motivation would not have any differential advantage.
If instead of DNA chains we think about complete individuals like us, the example works the same.
Obviously, if we consider that from a certain level of complexity or when certain functions appear, all the chains (or individuals) feel, then it would seem that sentience plays a role in evolution, but simply what would be happening is that sentience is a byproduct of something else. And it is that other thing (complexity, function) the thing that is being selected, not sentience. Sentience would not be useful: it would be inevitable.