Hacker is an excellent philosopher and a very clear writer. He starts from broad categories to look at human nature and what it makes sense to say of the nature of sentient animals, insentient animals, and inanimate things.
The main relevant chapters are:
1. "Agents and Actors",
2. "Teleological Explanation", and
3. "Reasons and Explanation of Human Action".
His main point is that many "unanswerable" questions in neuroscience and behavioral science are simply nonsensical because they play with conceptual confusions.
I would also highly recommend his sequel book "The Intellectual Powers: A Study of Human Nature".
Quite honestly, I'd give it a shot straight up, and pay close attention to references. I suspect Sapolsky will point you to the foundational works as necessary.
(I've not read this book of his, or any others, but I've seen numerous lectures and interviews, and read several of his papers and essays. He's an academic, but one who explains things exceedingly clearly, and documents sources. Sort of the best of all possible worlds.)
I can't say for sure as I haven't read it, but my general impression of Sapolsky is that he's very good at explaining things - in other words not unnecessarily abstruse.
I'd say that it's friendly enough. The appendices provide short primers on neuroscience, hormones, and proteins, and help make sense of the rest of the book. I'm about 1/3 of the way through and every day I have something new that I'm excited to tell my wife about.
I haven't read his new book, but I've read most of Sapolsky's older books and they're all excellent. "A Primate's Memoir" and "Why Zebras Don't Get Ulcers" are my favorites.
