We may wonder how many grains of sand make a dune, of how many molecules of water make a liquid. (John Conway would argue that it takes a single spin-1 particle to have free will, but I digress.)
The same way, even if individual chemical reactions are simple (you don’t want to use that phrasing when talking with a biologists) or neural activities are simple (likewise, with a neuroscientist), it does not mean that the collective process is simple.
