The book starts out strong and crunchy, with good data on how perception works. When Pinker moves from perception to society, however, he slides into less verifiable, more subjective territory. His assessments of why people think and interact the way they do sound reasonable, but they rely on a lot more conjecture than his material on perception does. Finally, he ends the book by sliding into near total subjectivity, as he addresses the ultimate concepts of God, free will, and morality.
The first part of the book is worth the price of admission by itself. It details what we know about how perception works, and how the brain (and the nervous system in general) "digests" incoming data. Where possible, he uses optical illusions and diagrams to demonstrate ideas. After reading this section, I could feel my cross-stimulating neurons locking onto elements in my visual field. It's a disconcerting lesson that perception doesn't just happen. Perception seems so intuitive and seamless that I have to learn the lesson over and over. While we experience perception as homogeneous and passive, it's actually choppy, active, and specialized.
Pinker promotes the computational theory of mind, which is that the basic function of the brain is computation. That struck me as a banal theory, until I remembered that it's me (the precious, ineffable internal me) that Pinker is talking about .
The second part of the book is less solid and more speculative because it's about human behavior, a notoriously difficult phenomenon to nail down. In the tradition of The Naked Ape, he relies on evolutionary history to understand human behavior. He offers one interesting, plausible insight after another. Why do pregnant women get morning sickness? To purge poisons that are common in a natural diet. Why does motion sickness cause us to barf? Because, in our evolutionary history, a disconnect between vision and balance has typically been caused by poison, and barfing gives us a shot at purging the poison. Why are people, especially kids, ticklish? In order to allow for more effective play-fighting (a pet theory of my own).
On point after point (standards of beauty, romantic love, emotions), Pinker portrays people across the world and from very different cultures as more or less the same. The question of how alike people from different cultures really are is worthy of a book unto itself. "Less different than you might think," is a fine answer that supports the evolutionary explanation of human behavior and counters the excesses of those who say that human behavior is culturally determined. But there's more to the answer than that.
Pinker offers an interesting mathematical model that explains why belligerence hasn't been weeded out of the gene pool. The more dangerous a warlike raid on the enemy is, the more likely an individual raider is to die and to be taken out of the gene pool. On the other hand, the more likely some raiders are to die, the fewer people there will be to divvy up the goods. Thus, a willingness to take part in dangerous raids doesn't get weeded out of the genes. (Notably, this makes the most sense for males out capturing females, as you see in the Old Testament conquest of Canaan.)
Appropriately, Pinker draws from a large and varied body of scientific findings and roams freely over dozens of topics. Sometimes I don't think he gives these topics the analysis they're due. His comment on racism, for example, equates racism with estimating the rate of dysfunctional or negative traits within a population. That definition leaves out whether one believes differences in behavior are genetically or socially caused, how readily and tenaciously one applies group stereotypes to individuals, whether one believes that God has cursed or blessed this race or that, etc.
Finally, in a short conclusion, Pinker addresses the mysteries of God, universal morality, free will, and consciousness. Here he drops the ball altogether. He suggests that universal morality, free will, and consciousness are intuitively valid truths that the human brain is simply not equipped to explain. To support the existence of universal morality, free will, and consciousness, he cites one's subjective certainty that they exist. Meanwhile, he dismisses belief in God, even though many people experience the same certainty that God exists. I don't see this as anything but intellectual dishonesty. Theists can rightly call foul for having their certainty excluded, and those who don't buy into universal morality and free will can see that it's unfair for Pinker to treat those phenomena as intuitively real, the way consciousness itself is.
How the Mind Works makes a fine companion to Dennett's Consciousness Explained. The books cover some of the same material, with Pinker addressing more social content, and Dennett tackling consciousness, one of the topics that has Pinker throwing up his hands. How the Mind Works is worth a read, but Consciousness Explained is more daring and better.