This book got me thinking about what, if anything, philosophers can contribute to scientific discussions. McGinn is a professional philosopher, but this book is (mostly) about a theory of the evolution of human intelligence.
The theory, in brief: Millennia ago, our ancestors were forced down from their arboreal habitat, for unknown reasons. They were poorly adapted to their new terrestrial home, and so an intense period of evolutionary selection ensued. The most fitness-enhancing phenotype turned out to be tool-use; it put our hands, now free from having to grasp branches, to good use. A period of synergistic coevolution of mind and hand followed. You need a state-of-the-art hand, strong but also capable of precision, to produce remarkable tools. But tool-making is also a cognitive act: you need to be able to think about things as having "ends", imagine future scenarios, etc. So, putting our idle hands to use encouraged the evolution of some sophisticated cognitive processes that underly intelligence.
All interesting ideas; however, they are presented almost completely without evidence. McGinn acknowledges this repeatedly throughout the text. He states that his role as a philosopher is to point out the kinds of explanations for the evolution of intelligence we should try to produce (e.g., theories should be able to explain the evolution of intelligence as a gradual process). His ideas, then, constitute one example of a theory that meets these criteria.
The bone I'd like to pick is this: I'm not sure that training in philosophy is particularly necessary for this kind of intellectual activity. Shouldn't an evolutionary anthropologist have an equal, or even a more informed, sense of the constraints on an evolutionary theory? An evolutionary anthropologist will not only know the kinds of theories that we must produce, she will also be able to defend a particular theory with empirical evidence.
This is not to say that philosophers shouldn't write books presenting scientific theories. Prehension is a thought-provoking book, and I'm happy I read it. I'm simply using this review as an excuse to analyze the claim that that philosophy can make unique contributions to a mature scientific field - I think any thoughtful, critically-minded scientist can do the same intellectual work when they present their research in articles or books.