Three possibilities come to mind:
Is there an evolutionary purpose?
Does it arise as a consequence of our mental activities, a sort of side effect of our thinking?
Is it given a priori (something we have to think in order to think at all)?
EDIT: Thanks for all the responses! Just one thing I saw come up a few times I’d like to address: a lot of people are asking ‘Why assume this?’ The answer is: it’s purely rhetorical! That said, I’m happy with a well thought-out ‘I dispute the premiss’ answer.
There are quantum phenomenon in a piece of bread. That doesn’t mean bread is conscious.
Penrose has never proved that the quantum effects affect neurons macroscopically.
Quantum computers run at near absolute zero temperature and isolated from all vibrations in order to maintain superposition. The brain is a horrible environment for a quantum computer.
Anesthesia is a chemical signal blocker. If consciousness was quantum, it couldn’t affect it.
Penrose’s work is “God in the gaps” or in his case “quantum in the gaps” explanation of consciousness. His claims were made before we had functional quantum computers and precise categorization of neurotransmitters that anesthesia chemicals bind to to block your natural neurotransmitters.
https://www.scientificamerican.com/article/how-does-anesthesia-work/