This book has covered far more territory than I have explored, but I've chosen to limit my comments to the phenomenon of cognitive stratification, which Herrnstein and Murray suggest has changed American society so much (perhaps more than any other phenomenon).
You'll recall the authors argued that in past ages, social position was governed far more by social position or wealth ("lineage and money") than by intelligence. Also that a large majority of the smart people in past ages were engaged in ordinary pursuits, living, working, and mixing with everyone else. "Social and economic stratification were extreme, but cognitive stratification was minor." (p. 27)
It's a commonplace in circles anthropological that technological changes produce social changes (at least that's what I was taught in Cultural Anthropology in 1970). Technology has grown by leaps and bounds in the last century or so; one excellent example is the progression from the first powered heavier-than-air flight in 1903, to the placing of astronauts on the moon in 1969. (I had relatives whose lifetimes included both dates.)
My last two posts demonstrated the phenomenon.
Early in the book, Herrnstein and Murray say: "Cognitive partitioning through education and occupations will continue, and there is not much that the government or anyone else can do about it."
"Another force for cognitive partitioning is the increasing physical segregation of the cognitive elite from the rest of society."
"The isolation of the cognitive elite is compounded by its choices of where to live, shop, play, worship, and send its children to school."
"Add to this the phenomenon known as assortative mating. Likes attract when it comes to marriage, and intelligence is one of the most important of those likes. When this propensity to mate by IQ is combined with increasingly efficient educational and occupational stratification, assortative mating has more powerful effects on the next generation than it did on the previous one. This process too seems to be getting stronger, part of the brew creating an American class system." (pp. 91-92)
Later, they reiterate:
". . . the funneling system is already  functioning at a highy level of efficiency, thereby promoting three interlocking phenomena:
1. The cognitive elite is getting richer, in an era where everyone else is having to struggle to stay even.
2. The cognitive elite is increasingly separated physically from everyone else, in both the workplace and the neighborhood.
3. The cognitive elite is increasingly likely to intermarry." (p. 114)
It is my opinion that these three phenomena were occurring then and are still occurring now, and there are obvious consequences, most of which, in my opinion, are highly undesirable, related to the authors' observation at the end of Part I of the book:
"What if the cognitive elite were to become not only richer than everyone else, increasingly segregated, and more genetically distinct as time goes on but were also to acquire common political interests? What might those interest be, and how congruent might they be with a free society? How decisively could the cognitive elite affect policy if it were to acquire such a common political interest? (p. 115; emphasis mine)
They give us this gloomy picture: "As of the end of the twentieth century, the United States is run by rules that are congenial to people with high IQs and that make life more difficult for everyone else." (p. 541)
Now, if I had my way, I would make the last two chapters required reading. They are:
21, "The Way We Are Headed," (which includes a discussion "The Coming of the Custodial State")
22, "A Place for Everyone," in which the authors discuss political philosophy, including that of the Founders. "The Founders saw that making a stable and just government was difficult precisely because men were unequal in every respect except their right to advance their own interests." (p. 531, emphasis in original)
Those who have read my blog see that I am a firm believer in the founding principles of this our country, as laid down in the Declaration of Independence and the Constitution, and an ardent opponent of anything and anyone who tries to subvert or pervert those principles because, as the authors say near the end of the book, "Inequality of endowments, including intelligence, is a reality. Trying to pretend that inequality does not really exist has led to disaster." (p. 551)
What can we do? Pray, pray, and pray some more! -- especially for the youngsters who are going to inherit this someday. Pray for them and educate them.
My sincere thanks to all who read this, and to people and sites like The Old Jarhead, The Catholic Caveman, Pajamas Media, The American Thinker, Jihad Watch, TH2, Anita Moore, Mary Ann Kreitzer, Thomas Sowell, Michelle Malkin, Alan Keyes, Tom Roeser, and all the others whose names slip my mind right now. God bless you all.
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 Being an intellectual as well as a physical packrat, I have saved several hundred blog and website posts just in the last few years. One of my folders is labeled "Culture War" and has 1880 files in 67 subfolders; one of which is labeled "Nanny-Servile State and Thought Police" with 63 files collected in the last 5-1/2 years. I have, in my national public affairs folder, 1842 files in 42 subfolders, one of which is called "Obamagrad" and has 464 files collected since January 2009. You get the idea: I think Herrnstein and Murray were on the right track because I have found out for myself that what they said has come to pass.