Very good points of thought.
I too often look at objects like rain for example and think, what are the odds of a single drop of water falling from thousands of feet up and hitting me smack dab on the arm while it's moving and more relevant to this discussion "where did it come from" or "where has it been". I think about how when people die and are buried then absorbed back into the earth their molecules become part of things like plants which are eaten by animals that walk the earth today.
On the subject of brain chemistry and functionality scientists are already building computer brains.
http://www.spiegel.de/international/...466789,00.html
I saw on TV this week some time a story about how scientists have also grown living brain tissue in a dish and are able to stimulate it to the point where it responds to stimuli. For example they connect a mechanical device that can sense light and sends the signal to the dish brain. The brain then sends responses back telling it to move away. Goes to your point of how free will is just reaction to a given stimulus based on learned behavior.