Complex sentence: His main argument is that emotions are "ways to think" for different "problem types" that exist in the world, and that the brain has rule-based mechanisms (selectors) that turns on emotions to deal with various problems.
Split into simpler sentences: His main argument is that emotions are "ways to think" for different "problem types" that exist in the world. The brain has rule-based mechanisms (selectors) that turns on emotions to deal with various problems.