This is a clear and well-structured discussion of the current state of knowledge about what makes a human mind. It carefully describes from where differences between humans arise, and how genetic and environmental variation can play out in different ways. The main message is that genes provide a set of potentials, or propensities, for how the organism can develop depending on the environment. Sometimes the genes limit the possible panorama of outcomes very tightly, sometimes only slightly, and sometimes a small set of possible outcomes are available. Importantly, in the latter case, the effects of pure chance can become crucial: if a system is set up to allow a divergence in development - a fork in the road, as it were - then the final result cannot be said to be neither "in" the genes nor determined by the environment. And yet it is innate.
I have a minor quibble: In a few paragraphs, the language has a few too many bio-jargon terms, which ought to have been edited away.
In the last pages, Mitchell makes a brief visit in the philosophical mine-field of determinism. He states that his view does not undermine free will, but he rejects dualism (the view that brain and mind are different). But he also writes "The mind is not a thing at all - at least, it is not an object. It is a process, or a set of processes - it is, simply put, the brain at work."
This seems to me to beg the issue. When he continues to affirm that the logical content of a thought - its meaning - can have a casual power in and of itself, by being an emergent phenomenon, then he seems to me to be much more of a dualist than he wants to admit. Now, I have absolutely no problem with this at all. The notion that the content of thoughts can have a causal power seems to me to contradict material determinism. The dualism (or rather theory of Worlds 1, 2 and 3) that Karl Popper espoused in "The Self and Its Brain" (with John Eccles) is, in my mind (!), a highly fascinating attempt at solving the mind-body problem.