There are few things more likely to provoke an emotional response than discussing IQ. It can get you labeled an elitist, a racist, or a jerk faster than just about anything short of wearing a swastika. This is all especially true if you're talking to the general public, rather than, say, researchers in the field of intelligence.
So, when James Flynn discovered in the early 80's that IQ scores have been going up about 5-10 points per generation, in every country on every continent for as far back as we have IQ scores to compare, he published his findings in academic journals and steered well clear of any layman's forum. He persisted in this even after the authors of "The Bell Curve" made frequent reference to 'the Flynn effect' (if only to try to say it didn't matter for their conclusions). The popular backlash against "The Bell Curve" probably did nothing to convince Flynn that discussing IQ in the public eye was going to result in anything constructive happening.
After more than 2 decades, Flynn has broken his silence with the public. He says the reason for this is that previously he only knew that the effect existed, but not why or what it really meant. Now, he believes, he does; hence this book. At the risk of being thought fascist, racist, or insensitive, we will now consider whether his book is any good or not.
First of all, a word about "The Bell Curve", which any book on the topic of intelligence or IQ is bound to be compared to (especially if it advocates any position which implies that IQ matters in any way, or that some people may have more intelligence than others). Murray and Herrnstein did not often go out of their way to avoid rousing passions or harsh judgement, and had an obvious (and conservative) political axe to grind. Even when their reasoning was sound (and often it was not), they deserve some criticism for the way in which they expressed it.
None of this is true of Flynn. One trick he uses to good affect, to engage our attention without inflaming our opinion so much that our reason shuts off, is to translate from intelligence to athletics. To say that some people not only have highly developed skills in a particular sport, but better than average general athletic ability, is not a controversial statement. It is still true even if, for example, Michael Jordan might not be as good at baseball as he is at basketball, and even if there are a few sports (e.g. horse racing) where he may be worse than average.
The question then, is this: why do the makers of IQ tests (e.g. the US military) have to keep reestablishing the baseline score for them? By definition the average IQ score should be 100, but what if ten years after it was developed, the average score is 105? One possibility is that what is increasing is just test-taking skill, nothing really related to intelligence. Flynn compares this to saying that decreasing times in the 100 meter race have nothing to do with actual increased speed, but just race-taking ability. In the absence of any real evidence, and especially since nearly every race distance we have has seen decreasing world record times, it is a good bet to look for something like improved diet, better training regimens for athletes, higher average height resulting in longer stride, etc.
Flynn lays out a range of apparent paradoxes. If IQ is normally quite similar between twins, even twins separated soon after birth, it would seem to be primarily genetic. How then can it be increasing over time, since we have no evidence that people with higher IQ have more children? When I talk to people 50 years older than I, why is it I do not feel myself to be conversing with someone of lower IQ? How about when I read letters written 300 years ago? If trends from the 20th century are projected backwards, by the time of the founding fathers we should have had a population of idiots. This is clearly not the case. Yet the Flynn effect is found across cultures as different as the U.S., the Netherlands, Argentina, India, and Kenya. If it is due to a cultural bias of the tests, it is so widespread as to render the term "culture" meaningless.
Flynn gives us the answers, as he sees them, with well-chosen analogies and copious references to well-designed studies. I won't pretend that I can summarize it here, but the shorthand is that IQ measures several fundamental kinds of intelligence, and we are developing some of them better and better over time, and others are languishing. Attempting to say more here would do a disservice to Flynn, in large part because he has covered some very difficult topics in under 200 pages, and with no fluff and very little repetition. It is hardly possible to be more economical with words than he is, and if I try to then it will misrepresent his assertions. It is possible to say that a key point is that, while there are general intellectual capacities that transfer between one skill and another, there are more than one of them, and some of them are increasing over time while others are not.
So, what is to be gained from reading such a book? Or, for that matter, from studying IQ at all? The reason why we are, as a society, hesitant to study intelligence, is that we value it more than at any time in our history. In 1000 A.D., John Plowman would benefit from being smarter, but he would benefit a lot more from being bigger and stronger than average, and perhaps also from being quicker and more nimble. Having a healthier immune system was more valuable from the dawn of cities up until about fifty years ago, when a high IQ could result in a better paying job, thus better health care, and thus for the first time you were more likely to survive a plague by being smart than by being hardy.
Thus, while we are still willing to say that someone is tall or short, ugly or beautiful (if they are male), quick or slow, often sick or not, we have become uncomfortable with saying that anyone is less intelligent than average. It now impacts their destiny in so many ways, it seems tantamount to saying they are a lower class of human. Fifty years from now, it may be beauty and social skills that matters more, and computing ability may have advanced so much that intelligence is about as handy as being tall or strong is today.
Until then, being able to think honestly about the one trait that is most crucial to our prosperity (individually or as a society) is something rare and to be prized. Flynn not only thinks intelligently on the subject of intelligence, he makes the reader better able to do so as well, a mark of the best kind of teacher. From the impact of early childhood to the impact of aging on our mental functions, he is able to shed a maximum of light while generating a minimum of heat, and that is a gift we could use a lot more of, in this century or any other.