I'm unsure why, but I've long been interested in the topic of free will. I made one of my rare suggestions that Portsmouth (NH) Public Library buy this book, and they acceded. As you can tell from the title, it's pro-free will. (But to be fair, I also have Robert Sapolsky's recent anti-free will book Determined on my "get" list.)
There's a blurb on the back from Steven Pinker:
Kevin Mitchell brings clear thinking and scientific rigor to a vital topic that leaves many people confused, caught between the preposterous alternatives that either humans are robots or that every time we make a decision, a miracle occurs.
That's a pretty good summary. Mitchell is a professor at Trinity College (Dublin) in the Genetics and Neuroscience department. Much of the book is devoted to exploring the long and tedious process by which evolution developed ever-increasingly complex neural systems for survival advantage. To be honest, my eyes glazed over in a number of spots. (Page 73: "We already saw transient multicellular behavior in the slugs and fruiting bodies formed by the aggregation of individual Dictyostelium amoebas. This kind of aggregative multicellularity is observed in many other species, across diverse groups of eukaryotes, and even in some bacteria called myxobacteria." OK, if you say so.)
I confess that pro-free will authors are pushing on an open door in my case. But Mitchell's argument here is careful and (seemingly) fair to the other side. He's even reluctant to provide his Official Definition of free will; I think the closest he gets is (page 282): "If free will is the capacity for conscious, rational, control of our actions, then I am happy in saying we have it." That works for me.
I believe Mitchell is making a strong science-justified claim roughly similar to the psychological argument made by Ken Sheldon in Freely Determined; there's a "hierarchy of human reality". At the lowest level, there's the physics and chemistry of interacting atoms and molecules; moving up, there's increasing complexity in cells, organs, and "systems". And it proceeds upward into relationships, society, and culture. Determinists only see causality working bottom-up: it's just those atoms bumping into each other that cause everything else. Mitchell and Sheldon say no: causality works top-down too. Specifically, your cognitive functions can work their will on the lower level too. And that means (ta-da) free will.
The usual disclaimer: ardent determinists and zealous free-willers (I'm pretty sure) are united in their beliefs having absolutely no effect in how they run their everyday lives. To use a common example: they pick out which shirt to wear in the morning, neither thinking too much about it, nor waiting until the molecules in their body do whatever they were predestined to do anyway.
Minor nit: Mitchell says (page 29) that the hydrogen nucleus "comprises a single proton and a single neutron." Ack, no: it's just a proton. (I assume he's right about everything else, though.)