Here is a mind game to ponder: It is well known that Google founders Larry Page and Sergey Brin have high IQs. Both sets of their parents are college educated and either academics or researchers. So which factor was more important in the success of these two technologists, their God-given cognitive talents, or their middle-class upbringing by people who could rightly be called intellectuals?

Increasingly, psychologists and sociologists would say their middle-class background and values far outweighed genetics or other effects. More specifically, kids raised in the relatively complex social environment that characterizes most middle-class homes have advantages over kids from working-class backgrounds. And the advantages aren’t merely better schools or teachers.

Child psychologists have estimated that children of professional parents have heard about 45 million words by the time the kids turn three. Youngsters from working-class homes have heard only 26 million words by that age. Welfare toddlers hear only 13 million. A rich exposure to words improves more than just vocabulary.  It also helps youngsters learn to deal with social abstractions. Psychologists say abilities in these areas are important because there’s a link between intelligence and the cultural practices of reading and writing.

Hold that thought as you consider the decline of the U.S. middle class and the rise of economic inequality. If smart kids are more likely to be raised by parents who are professionals, the country may be in trouble. The high-school graduation rate in the U.S. is lower now than it was in 1970. The college graduation rate for those under 30 has risen only slightly in the past 30 years. Economists say the relative supply of college graduates grew just 2% annually between 1980 and 2005, compared to a 3.8% annual rise for the 20 years prior.

And many of those college graduates have trouble finding jobs commensurate with their education. Thus, it is likely that significant numbers of them will become part of a lower socioeconomic class. The combination of downward economic mobility and subpar graduation rates doesn’t bode well for future generations. Or at least that is one conclusion from work by psychologists who studied IQ differences between sets of seven-year-old twins. It turned out that kids raised in high socioeconomic households were more likely to inherit high IQs from their parents. For those living closer to the poverty line, poor living conditions seemed to swamp out any effects of having parents with high IQs.

So here is the other half of the mind game: Suppose the parents of Larry Page and Sergey Brin had been unable to secure positions in research or academia and wound up working as telemarketers at call centers. Would their sons still have been savvy enough to invent Google? The answer is important. It could tell us whether we may be witnessing the creation of an IQ gap where large numbers of Americans will lack the cognitive skills to prosper, even if their parents are whip smart.