I don't believe in free will. I also think it's ludicrous that so much of the world does. The typical reaction I get when I talk to someone about free will is "What do you mean I don't control my own behavior? Of course, I control my own behavior!" And my response is "you do" IF we just look at your life in segments: YOUR decision to get out of bed in the morning, YOUR decision to pour yourself a glass of juice, YOUR decision to order take-out. But real life isn't segmented. In real life, everything's connected. All our decisions have external roots whether they be distant learned behaviors (you learn how to be a civilized person, waking up, pouring juice in a glass, going to school or work) or at-the-moment course changers (a take-out menu was hanging from your door knob when you got home).
The special advance of humans is our level of sophistication in and dependence upon learned behavior, not free will. Without learning, we are no more advanced than apes. Without learning how to make decisions, we can't make them. Without encountering external stimuli, we can't make decisions between them. Every decision we make, every preference we have is rooted in something we learned in the past and are encountering in the present.
I was thinking a lot about free will when I took my first psychology class. Though it wasn't discussed in the book or by the teacher, I noticed that the analysis of behavior as the result of a combination of environmental and genetic factors didn't touch at all on free will. Psychologists left that out entirely. And for good reason, I came to conclude. Free will breaks a basic law of physics. You can't create something from nothing. You can't spark a truly original thought or behavior. The most you can do in regards to originality is take from your past and your present and rely on skills you've learned, your ability to reason, to draw, to compose music, and combine what you've learned into new and unique arrangements. Our only originality is in rearrangement and advancing upon someone else's last step by applying some learned system of logic or skill or whatever.
However you view the originality argument, it's clear we're never free from external influence, whether that be from our parents and ancestors via genetics or the things and people we've encounter or are encountering via environment. Not only are we not free of these things, genetics and environment, but that is all we are, a complicated intermingling of the two. Once you really think about it, there is no room for a little spirit inside an individual that is his own agent for purely originating thoughts and behaviors. Such an idea is preposterous, that anyone's thought or behavior could exist like the geometric symbol, ray, with one single source point and an arrow outward in a single direction. No, once you really think about it, the world and the laws that govern it are such that there are no rays, no clean single source points, but rather all thought and all behavior, human or otherwise, is in a continual state of flow or flux from one event to the next, sometimes a thought enters the head and is stored, but that energy has flowed in from the outside and will move around inside every time it is retrieved and it is only retrieved when something on the outside reminds us of it or we're actively seeking it because of some external influence whether that be a person, an idea or an inanimate object. And that thought will flow out with every remeberence and utterance we make, and will flow out of us and into something else when our bodies stop living, obeying the logically flowing laws of our physical world, unlike the myth of free will.