The central hypothesis of this book is that genetic differences between human groups (in particular, differences in average native intelligence) have been an important factor in human history. The opposite hypothesis--that genetic differences between human races are insignificant--is at present the conventional hypothesis and the only politically correct one.
Hart is not someone whose views I trust. My instinct told me to probe deeper to find out where he is coming from.
It took a while, but I managed to find my way to this essay by Hart, in which he argues for allowing Americans to voluntarily segregate themselves into a white state, a black state, and a multiracial state.
What I would suggest is reading his essay, but substitute "academic intellectual" or "Jew" or "right-winger" or "left-winger" every time he uses the word "black." I don't think that the essay would change much, which tells me that he was suffering from a rather strong racial bias.
In his book, Hart argues strongly for accepting the concept of a race. He draws an analogy between human races and breeds of dog. I find this unconvincing. I don't know much about dogs, but my impression is that pretty much any healthy greyhound is going to outrun any healthy poodle. Similarly, my impression is that some breeds of dogs are essentially uniformly more intelligent than other breeds. Some breeds are uniformly more placid. Etc.
My impression of humans is that blacks are not uniformly more athletically gifted or uniformly less intelligent than whites. In fact, the distributions overlap considerably. Hence, for me the analogy with breeds of dogs does not work.
I believe that IQ measures something at an individual level. I believe also that if you take two groups of people and one group has a higher average IQ, then that group will have an advantage in a competition that involves intelligence. The academic departments with higher IQ's are likely to publish more papers. Firms whose workers have higher average IQ's are likely to have higher productivity (although not necessarily higher profits, because wage rates can adjust) than competing firms. Countries where populations have higher average IQ's are likely to have better government and higher GDP per capita than countries with lower average IQ's. And it may very well be that, historically, countries that developed more quickly and gained technological leadership did so in large part because of higher average IQ's.
But blacks as a group do not compete with whites as a group. Groups that happen to contain many blacks may compete with groups that happen to contain many whites. And, given the large within-group variation in IQ's, it is quite plausible for a group that contains many blacks to out-compete a group that contains proportionally fewer blacks.
I also believe that it is difficult to change individual or group IQ's. The Flynn effect suggests that some environmental factors influence group average IQ. But as far as I know, we have no study that offers us a promising policy tool that uses environmental factors to affect IQ.
I think that recognizing that IQ is important and yet difficult to change is somewhat discouraging for those whose project is to remake the world. If the populations of underdeveloped countries have low IQ's that cannot be improved through nutrition or health care, then there may not be any policy mix that works.
The project to remake the world in terms of income distribution tends to presume that education is the answer. But if the main causal factor is IQ, then education will not work--at least, not to the extent that people hope.
My point is that I think that much of the interesting things to say about IQ, including many politically unpalatable propositions, can be said without buying into Hart's emphasis on race.
At an analytical level, the book leaves a lot to be desired. Often, Hart writes as if there is some "magic number" that average IQ has to hit in order for society to achieve a new stage of development. That strikes me as pretty dubious. But even if I were more convinced by the analysis, I would still believe that it makes more sense to look at a person as an individual rather than in terms of racial identity.