Many of the people who ask this question don't really want an answer, because they're already committed to leaving "room" for an immaterial soul. So the simpli

Many of the people who ask this question don't really want an answer, because they're already committed to leaving "room" for an immaterial soul. So the simplicity of the answer depends mostly on the ideological commitment of the questioner. I'm game if you are, though. You might start by thinking about a modern digital computer. It's made up of a very large number of very small devices (transistors) that sling populations of electrons back and forth. The brain is made of a much larger number of less-small devices called neurons, that sling bigger populations of bigger objects (organic molecules) back and forth. So according to the basic understanding of QM that tells us relative indeterminacy increases when considering smaller objects, the functioning of the human brain is marginally more predictable than the insides of a modern computer.