[yossarian]

Do you realize how ironic it is that you talk about occurrences in terms of chemicals and biology when chemistry and biology is just another human created model of reality that is only used because it's useful?

Are you a reductionist? ie. Do you recognize that biology is derived from chemistry and chemistry from physics? And do you think this principle applies to the whole universe?

If you're a reductionist, then I say, "Prove that reductionism is true." (There is counter evidence showing its false in condensed matter physics, though, so faith in perfect reductionism is pretty neatly shattered by experiment)

If you're not a reductionist, and take biology and chemistry to be emergent phenomenon, then you should also be very willing to take ghosts and spirits as emergent phenomenon depending on the subjective utility of those beliefs.

Just because you have an alternative explanation of some phenomenon does not mean that any other explanation is false. This is true in science all the time - in quantum physics for instance the Feynman Sum over Histories method is contradictory to the conventional method, yet both are true at the same time. This applies to macro-phenomenon just as well as quantum mechanics. (Although the sum over histories model actually applies to all scales not just micro)