Sorry to belabor this topic, but I haven’t been able to stop thinking about it!
Does the fact that each person is different, both from the nature side (except identical twins) and the nurture side, mean our decisions are unpredictable? The arguments that our decisions are the result of electro-chemical processes seem unassailable; we can’t escape the laws of physics after all. When presented with a decision the brain will go through predictable processes, reviewing memories of similar choices and weighing the benefits/dangers of each possibility, undoubtedly triggered by electro-chemical events, but the memories recalled, variables considered, and things valued will be different in each person. One may say that this is obvious, and doesn’t mean anything, but I think it may be logically solid way to sneak free will in the backdoor. A decision will be the immediate result of a preceding electro-chemical process, which is itself the end of a casual chain that reaches back to before the person was conceived, but the experience since birth and the genetic makeup will be different in each individual. Say we knew a persons history (I eat cheerios for breakfast almost everyday) we would still have to know his genetic predispositions (when I'm likely to try something new) in order to attempt to predict what the decision will be, even granting that we know the electro-chemical status of the brain throughout the decision making process. No one can "know" what anyone will do, they can do whatever they want, and people often surprise themselves. Two brains experiencing the same electro-chemical conditions could make different decisions, or even if it is a decision made by the same person everyday (like what to have for breakfast), they will have accrued 24 hours more experience between each one, making a different decision possible every day (I think I"ll have eggs for breakfast tomorrow!). The different decision may be a result of a change in outlook on life, health, or just mood, but it can alter the decision. Our free will doesn’t come from an ability to bypass the laws of physics or logic but from our undeniable uniqueness. We may be meat machines, but we, and the world we live in, are so complex that a decision will never be considered the same way twice. We can’t escape the laws of physics any more than we can escape our past or our genes, but they all combine to create an infinite amount of unique conditions since the last two are not nearly as static as the first. Every choice anyone encounters has never been approached by the unique combination of genes/experience that they bring to the table at that very moment. Their choice is therefore completely unique and unpredictable. It may not be the normal notion of free will, but it does allow us to own our actions.