More so than the other books in this series that I have read so far, this volume tends to organize each chapter around summarizing one or more studies related to a given theme and then pointing the reader to further works. By this I mean that I didn't come away from the book feeling as though I had read a unified narrative so much as a collection of articles on various broad topics.
The chapters didn't really feel as though they were building upon the previous chapters--I felt very much as though I could open the book at any given chapter and start reading. Also, the key point of each chapter tends to be pretty short when you come right down to it--the bulk of each chapter seems to be occupied by recapitulations of the studies that were conducted. And those studies themselves are heavily biased towards standardized intelligence tests and studies of intelligence tests. But you don't get a very informative sample or description of the content of any of these tests. As such, this volume wasn't quite as interesting or satisfying as some of the other books.
Here's the Table of Contents (I've actually used the sub-headings for each chapter, as they are more informative as to that chapter's contents):
- How Many Types of Intelligence Are There?
- What Happens to Mental Abilities As We Age?
- Why Are Some People Cleverer Than Others?
- Are Differences A Result of Genes or Environment or Both?
- Does Intelligence Matter?
- Is Intelligence Increasing Generation After Generation?
- Psychologists Actually Agree About Human Intelligence Differences
The chapter =begins by noting that intelligence tests indicate one extremely broad category of intelligence (general intelligence) that is then divided into four broad areas of ability: Verbal Comprehension, Perceptual Organization, Processing Speed, and Working Memory. Each of these encompasses a smaller set of sub-abilities. For example, Perceptual Organization can be tested in terms of picture completion, block design, picture arrangement, and matrix reasoning.
The chapter also introduces another way of categorizing intelligence, developed by John B. Carroll: broad visual perception, broad auditory perception, fluid intelligence, broad retrieval ability, crystalized intelligence, broad cognitive speediness, general memory and learning, and processing speed. But to know what any of these categories actually mean, you'll have to look elsewhere for descriptions of Carroll's work. Overall, an interesting introductory chapter that lays out some of the key concepts.
Chapter 2 boiled down to one salient point based upon the most recent research (though as with everything in the intelligence testing field, there's no clear consensus): as you get older, your mental processing speed slows down. This slowdown tends to cause a domino effect in your cognitive ability and reduce your general intelligence in areas related to how fast you think. Less time-dependent processes don't reflect this decline. And some people hold onto their mental acuity better than others. Not a really gripping chapter, though it raised some fear in me as I age.
Chapter 3 doesn't really provide an answer to the question of why some people are smarter, it just summarizes the competing views on the subject. Larger brain size corresponds slightly with higher intelligence scores, but not enough to explain everything. The size and structure of different parts of the brain correspond to different talents. It could be the electrical activity between neurons in the brain, but studies are inconclusive. The chapter also cites studies that enforce something that seems totally dubious to me: that increased reaction time correlates with higher intelligence. I played sports a good bit through high school and college, though strictly as a dabbler with slight talent. I did play alongside a number of people who were highly rated athletes, however. Some of them had astonishly quick reflexes and reactions. And I saw absolutely no evidence that these people were smarter than the average bear. So I need more convincing on this one. This chapter would have been more interesting if any of the studies had reached any interesting conclusions.
Chapter 4 surveys a number of studies and boils down to the somewhat uncomfortable conclusion (if you're a parent or interested in adoption) that genes account for more similarity and variation in intelligence scores than any other factors, including shared environment (school, community life, parental upbringing) and unique personal experiences. But no one knows just what genes code for general intelligence or its sub-categories. The explanations of how the studies were carried out fell flat for me here, bogging down what would otherwise have been an interesting chapter.
Chapter 5 uses a number of studies to come to the interesting conclusion that a higher score on a generalized intelligence test correlates more highly with better job performance than any other evaluating method in common use (including structured interviews, samples of relevant work from the applicant, job experience, age, and so forth). The recommendation is to give applicants a standardized IQ test, a structured interview, and something called an integrity test to get the best possible result. Which will still be a best guess, of course. I for one wanted to know more about what an integrity test is and how it works, but that's outside the bailiwick here. No mention here of whether higher general intelligence assists in any other areas of life. This chapter was interesting more for the topics it introduced but did not explain than for what it revealed, but it was okay.
Chapter 6 is, after chapter 1, the most interesting chapter of the book in my view. According to all the standardized IQ tests, including those that deal with abstract reasoning seemingly devoid of a cultural context, people in many different countries are getting progressively smarter. But at the same time we have SAT scores and the like dropping. No one is sure what this means: are people getting smarter, or are we somehow indoctrinating each successive generation with greater proficiency in the types of thinking and problem-solving that the tests measure?
Chapter 7 summarizes what psychologists actually agree upon concerning education, which essentially consists of agreeing on what they don't know:
- Genes influence intelligence in an unknown fashion
- Environmental and nutritional effects on intelligence are unknown
- Nobody knows why intelligence scores are increasing
- Nobody knows why different groups tend to score higher or lower than others
- We don't know enough about other mental abilities like wisdom, creativity, etc.