The second broad implication is that parental SES is important but not decisive. In terms of this figure, a student with very well-placed parents, in the top 2 percent of the socioeconomic scale, had only a 40 percent chance of getting a college degree if he had only average intelligence. A student with parents of only average SES – lower middle class, probably without college degrees themselves – who is himself in the top 2 percent of 1Q had more than a 75 percent chance of getting a degree.

Once again, the common stereotype of the talented-but-disadvantaged- youth-denied-educational-opportunity does not seem to exist in significant numbers any longer. Only seven-tenths of 1 percent of whites in the NLSY were both “prime college material” (IQs of 1 15 or above) and markedly disadvantaged in their socioeconomic background (in the bottom quartile on the SES index). Among this tiny group, it is true that fewer than half (46 percent) got college degrees. Those who did not, despite having high IQs, may be seen as youths who suffered from having a disadvantaged background. But recall that this group consists of only four-tenths of 1 percent of all white youths. A category of worthy white young persons denied a college education because of circumstances surely exists to some degree, but of such small size that it does not constitute a public policy problem.

What about another stereotype, the untalented child of rich parents who gets shepherded through to a degree? Almost 5 percent of white youths had below-average 1Qs (under 100) and parents in the top quartile of socioeconomic status. Of those, only 12 percent had gotten college degrees, representing just six-tenths of 1 percent of white youths. Judging from these data, the common assertion that privileged white parents can make sure their children do well in school, no matter what, may be exaggerated.

Or this:

For example, imagine a white person born in 1961 who came from an unusually deprived socioeconomic background: parents who worked at the most menial of jobs, often unemployed, neither of whom had a high school education (a description of what it means to have a socioeconomic status index score in the 2d centile on socioeconomic class). If that person has an IQ of 100 – nothing special, just the national average – the chance of falling below a poverty-level income in 1989 was 11 percent. It is not zero, and it is not as small as the risk of poverty for someone from a less punishing environment, but in many ways this is an astonishing statement of progress. Conversely, suppose that the person comes from the 2d centile in IQ but his parents were average in socioeconomic status which means that his parents worked at skilled jobs, had at least finished high school, and had an average income. Despite coming from that solid background, his odds of being in poverty are 26 percent, more than twice as great as the odds facing the person from a deprived home but with average intelligence.

In sum: Low intelligence means a comparatively high risk of poverty. If a white child of the next generation could be given a choice between being disadvantaged in socioeconomic status or disadvantaged in intelligence, there is no question about the right choice.

On your second point, the estimate in step 3 needs to be adjusted by step 2 as there are two parents. Step 2 is whole genotype correlation.

Even if heritability stayed the same from one generation, that wouldn’t necessarily indicate intergenerational genetic transmission. That’s because equally heritable but different causes may underly the trait for each generation.

I would guess that there are some traits like g, work ethic, etc. which are valuable and transmitted from one generation to the next. But with a changing economy/society I would also guess that the genes/environments which matter also change.

I wonder how big an impact that might have.

Bowles and Gintis’s implicit assumption of a constant environment and heritability is fair given the purpose of their paper (and I tend to think it is also a broadly accurate assumption). Over the time covered by the generations of interest, there has been a relatively consistent correlation between income and IQ and parent and child IQ, and consistently high heritability of IQ in the populations of interest. As the paper shows, the specific heritability calculations are not the most significant factor in obtaining the result – it is the magnitude of the income-IQ correlation (or income-other genetic factors correlation) that tends to limit the degree to which IQ and genetic factors can be used to explain the strong correlation between parent and child income.

After all, a trait may be highly heritable but not pass on from one generation to the next. This is because the relevant genes and environments may differ from one generation to the next.

So I understand how we can make claims about genes and income within a generation, but by what logic can you extend this to intergenerational transmission?