Rapidly accumulating evidence from biology, evolutionary psychology, and cognitive neuroscience suggests we are not causal exceptions to nature. There is no categorically mental agent or soul-essence floating above the brain which can exert a choice-making power that’s independent of neural processes. There’s nothing supernatural or causally privileged inside the head, just as there’s nothing supernatural outside it.
This makes perfect sense. If we atheists hold on to "free will" we are implying that we have contra-causal freedom. That our power of choice is not predicated on the biological self. That somehow we are able to transcend (in some way, in a limited way) the physical universe (and the "laws of nature") and make free choices. We border on invoking some paranormal phenomenon in even intimating that freedom of choice is contra-causal.
When you sit down and really think about it, it is irrational to suppose that we are free--that we have contra-causal freedom. Thus, as Clark rightly suggests, we ought to forsake the irrational belief in the little god. Richard Dawkins talks of the illusion of design in nature--living organisms may look designed but in fact are not. Realizing that free will is an illusion as well is the next step.
I had a preview of Tom Clark's ideas on the illusion of free will a couple of weeks ago. I also heard him on the Skeptics Guide to the Universe podcast. I've been nodding my head ever since. I'm really excited about this. As always, for us ontological naturalists science will be the enterprise that will unravel the mystery and show us the causal links and mechanisms by which human "free choice" comes about and operates. Among others, "genetic endowment, upbringing, and social environments" are surely prime factors.