This is very interesting. I had come to the conclusion myself that perhaps the emergence of sentience helped to drive the Cambrian Explosion, so I googled a couple of terms and came up with this. I thought it inherently unlikely that I was the only person to have thought of this, even though the subject of consciousness/sentience (linguistic minefield!) receives such scant attention from the scientific community generally.
At its most basic level, sentience likely comprises just two experiential components: pleasure (mmm, that’s nice, I’ll have a bit more of that), and aversion (yuk, that’s nasty, no more thanks). Aversion probably diverged very early on into physical pain and disgust. Once animals evolved the necessary equipment to be sentient, even at this most rudimentary level, this would become a powerful driver of evolution. There would be a very large survival advantage to having a receptor which could not only detect a valuable nutrient but which was also connected something which could generate the “mmm!” experience – an animal possessing this would then naturally seek out what was good for it. Similarly, a receptor for a common toxin connected to “yuk!” would also enhance the chances of survival. And receptors which linked mechanical damage to the pain experience would powerfully cause an organism to protect itself from injury.
My suspicion is that sentience has something to do with nervous systems - you need one to be sentient, pretty obviously, and maybe it's the case that simply possessing one gives you sentience; the more complex the nervous system, the more complex and discriminating the sentience. As for what sentience is, how it arises, where it comes from - we do not seem anywhere near being able to answer this in any scientific manner because it is very difficult to think of hypotheses that are testable.
Galen Ives, Sheffield, England.