There is no such thing as the soul in the sense of an abstract, metaphysical concept. Believers will note that the soul is immaterial: its existence is not subject to empirical methods. (Otherwise, it is tempting to ask: Exactly when during evolution were humans bestowed a soul?)

If an immaterial soul influences (or is somehow intertwined with) our bodies, it must exhibit a change in the electrons that comprise us (otherwise it cannot affect us and we should discard the concept of souls altogether). The Dirac Equation describes how electrons behave at normal energy levels and has been verified in every related experiment. If souls exist, then the equation is wrong and we must throw our knowledge of physics out the window. (Who needs cell phones and satellites, anyway?)

The soul introduces complexity: How does the soul physically influence us? Do its interactions preserve conservation of information? What is its relationship to Lorentz invariance? These are for theists to answer, for they posit the existence of the soul.

Ockham’s razor suggests we should lean towards simplicity. The natural world is simpler to describe without metaphysical souls.