The Son Also Rises: Surnames and the History of Social Mobility gets my vote for the most important economics book of the 21st Century (supplanting A Farewell to Alms , by the same author).

Gregory Clark, an economist at the University of California, Davis, shows that social mobility is much slower than we’ve been led to believe. Our focus on the correlation between parent income and child income misses a lot of other important stuff. Making $300,000 per year as a doctor is not the same as making $300,000 per year selling subprime mortgages. What might lead one to want to look carefully?

… the twenty-seven adult great-great grandchildren of Charles Darwin , born on average nearly 150 years after Darwin, are still a surprisingly distinguished cohort. Eleven are notable enough to have Wikipedia pages, or the like, such as Times obituaries , devoted to them. They include six university professors, four authors, a painter, three medical doctors, a well-known conservationist, and a film director (now also an organic farmer).

Instead of working from readily available data, a trap into which most academics fall, Clark figured out that dusty old registers of who was a doctor, who was a university student, who was a member of parliament, etc. could be used to track the success of families over centuries. To what extent does your great-grandfather being a physician predict your likelihood of being a physician? To a surprising extent in stable class-stratified England. How about in the United States, land of personal reinvention? To roughly the same extent. How about in Sweden, where every conceivable government program to reduce inequality has been implemented? To roughly the same extent.

On the flip-side, what if your extended family has had a history of low educational attainment, low income, and low social status? Chances are so will you. If by a combination of hard work and luck you’ve managed to achieve much more than your ancestors, unless you are able to mate with a person from a historically high-status family, your children are statistically likely to be more like your parents, aunts, and uncles than they are to be like you.

Every family will eventually regress to the mean, but it may take hundreds of years, not the handful of generations that the correlation between parent income and child income would suggest.

As you can see from some of the Amazon reviews, Clark upsets a lot of American readers by suggesting a genetic basis for “social competence”. This is not news in Asian cultures, however, as far as I know. “The family is more important than the individual,” is common advice given in India when a son or daughter is reaching the age of marriage. Where the Indians and Chinese have millennia of experience, though, Clark has data to back up his conclusions.

But some groups within a society resist regression to the mean, you might object. There are some groups that are persistently successful or persistent unsuccessful. Clark correlates this tendency to have higher correlation from generation to generation with lower rates of intermarriage (“marital endogamy”). Coptic Christians, for example, were a disproportionately high status group following the Arab conquest of Egypt. The low-status Coptics couldn’t afford to pay the higher tax rates on non-Muslims so they converted to Islam. According to Clark, Copts have maintained their high status within Egypt for nearly 1400 years and tend to occupy high-status occupations even here in the U.S., e.g., they are 13 times more likely to be medical doctors than average (compare to 4-5X for Jews and Asians).

Perhaps the hardest section for a parent to accept is that the home environment created by the parent is more or less irrelevant to a child’s success. Clark cites the most important studies on the correlation between adopted children and their adoptive parents. There is virtually no correlation for intelligence, income, the tendency to attend four years of college, etc. These things are highly correlated, of course, for the typical parent and child but the studies suggest that is only because the typical parent and child have genetics in common. As a parent and a teacher I find it almost impossible to accept these research results and the logical conclusions that follow. At a minimum, if an average child were adopted by Tiger Mom (my review of that book; a blog posting on the NYT review), wouldn’t the resulting adult end up with the useful skill of being able to play the piano or violin? And this video makes me think that my work as a helicopter instructor has not been in vain.

Clark’s book came out at roughly the same time as the English-language version of Thomas Piketty’s Capital. Thus I think that it is accidental that The Son Also Rises provides probably the best refutation of Piketty’s thesis:

The lineage of Charles Darwin is a nice illustration of how large the families of the middle and upper classes could be in preindustrial England. He descended from a line of successful and prosperous forebears. His great-grandfather Robert Darwin (1682– 1754) produced seven children, all of whom survived to adulthood. His grandfather Erasmus (1731– 1802) produced fifteen children (born to two wives and two mistresses), twelve of whom survived to adulthood. His father, Robert Waring (1766 –1848), produced six children, all of whom survived to adulthood.

In a social environment where all these children had to be privately educated, dowries needed to be provided for daughters, and estates were divided among children at death, human-capital theory would predict that the heedless fecundity of the English social elites of these years would lead to rapid downward social mobility . The lower classes of preindustrial society, producing only modestly more than two surviving children per family on average, would be able to concentrate resources on the care and education of their offspring and see them rise rapidly on the social ladder. …

But we see no signs that social mobility rates in England slowed as the upper -class groups produced fewer children. Instead, as chapter 5 shows, the intergenerational correlation of status remained constant for education and wealth. By implication, human-capital effects on social mobility must be modest. Status is strongly inherited within families mainly through genetic or cultural transmission, or both.

We can simplify this by considering the case of a rich family with 20 children and a rich family with 1 child. If Piketty is right the rich family that has just 1 child should have substantially wealthier descendants than the equivalently rich family with 20 children. The data show instead that those 20 children were able to become wealthy on their own account almost as easily as the only child who inherited everything. (Clark’s data are not affected by primogeniture inheritance customs because he looks at all descendants with the same surname.)

Note that the studies of adopted children also refute Piketty. If being reared in a relatively wealthy family didn’t make the adoptees wealthy then family wealth can’t be the main determinant of life success (admittedly the stats are thin for children adopted into the crazy rich families that are Piketty’s primary focus).

I’ll write more about how to apply Clark’s new work to everyday life, but here’s a preview:

But in fact the correlation of longevity between individual parents and children is very low. For the people dying in England in the period 1858– 2012 with the rare surnames used in chapter 4 , we can measure the correlation of longevity between fathers and sons for more than four thousand sons surviving to at least age 21. That correlation is only 0.13. If we take the average of both parents’ ages at death, that correlation increases to 0.26. But it is still low. 9 In reality, your age at death is not strongly predictable from your parents’ age at death. All those saving more for retirement simply because both their parents are fit, healthy, and in their nineties should stop immediately. Your expected additional longevity relative to the average is only three years.

In the meantime elite university admissions offices have either come to the same conclusions as Clark or they are responsible for the persistence that he sees. Universities such as Harvard and Yale preferentially admit the children, grandchildren, siblings, etc. of graduates. This could be because they recognize that a family that was successful in the past is likely to be successful in the future. Or it could be that a Harvard or Yale degree is enough to guarantee success (albeit a lower income than a California prison guard) and, by giving preference to “legacies,” the elite universities are the institutions that are creating the persistence in status and success that Clark attributes to genetics.

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