Why do rich parents give birth to rich kids?

The kids and grandkids of the wealthy tend to be wealthy. Well: that's not quite true. Kids of American football players and lottery winners and those who get wealthy through luck often squander their inheritance. And while giving your kids money makes them richer, it doesn't tend to make their kids (i.e. your grandkids) richer.

This little paradox has driven researchers to wonder why wealth is persistent, if it's not purely handing down the cash. Traditionally, scholars have divided into two camps: nature and nurture.

Families stay rich because they have prudent genes that stop their ancestors from squandering their fortunes, and because they have genes that make them good at earning more money. Or families stay rich because they give their kids skills through schooling, speaking lots of words at home, having books around for them to read, pushing them into high prestige careers, and linking them up with connections.

Lots of research points in the direction of genetics, finding that genetics explains about 50% of every important human trait, while the other 50% is largely down to 'nonshared environment'—rather than 'shared environment' (i.e. family upbringing).

For example, the gold standard meta-analysis, recently published in Nature Genetics, looked at 17,804 traits over 2,784 publications studying 14,558,903 twin pairs, and found that the average genetic contribution to a trait was 49%.

This extends to complex facts about a person, like lifetime income and wealth. For example, among Swedish twins wealth was found to be about 20-40% heritable (i.e. down to genetic factors), while 20-year average income in men was about 60% heritable.

But comparing identical and non-identical twins isn't the only valid study design for dissecting the differing impacts of nurture and nature (though it is valid). You can also look at twins reared apart and you can look what happens when a child is adopted into another family—do they end up looking like their biological or adoptive parents?

We know that adoption can temporarily boost IQ but other evidence suggests this may be driven by non-randomness in the study design or peter out once the child leaves the family environment. What's more the gains might boost measured IQ but not intelligence.

But a new study suggests that adoptive parents are the main drivers of children's wealth, with biological parents unimportant by comparison. However, this new study finds that the result is not through transmitting human capital down the line or even through children earning higher income, but simply through transferring cash or learned prudence—i.e. kids investing better.

The paper (pdf), from Sandra E. Black, Paul J. Devereux, Petter Lundborg, Kaveh Majlesi, looks at a sample of 2,519 Swedish adoptees born between 1950 and 1970, and finds that the rank of a child's wealth is correlated 0.23 with their adoptive parents' wealth (and 0.65 when bequests are taken into account). By contrast it correlates only 0.12 with the rank of their biological parents. The results for levels of wealth, rather than ranks in the wealth distribution, are very similar.

So does this tell us that the rich buy private school, tutor their kids, make them learn violin, and help them with connections and so on? No! The authors rule out this possibility, and suggest only two possible options: financial gifts (which they cannot track) and learned prudence (which they provide evidence for in another paper).

(Note, the authors tell us that income is more biological than adoptive. Human capital is not being driven by upbringing. We might reasonably guess that a couple of generations down the line nature is driving wealth more than nurture.)

I work for a think tank so I think about policy conclusions and I think this fits pretty nicely with Adam Smith Institute ideas. What can you do to raise people's wealth? None of the things that pushy parents do seem to help their kids be rich except two: give them cash, and teach them to save more and save better.

The latter seems a bit more politically practicable, but the problem is that most financial education schemes seem to have no impact. Maybe the only way you can teach this stuff is something as long-lasting and comprehensive as being adopted. (I'm open to being wrong here—it would be great if there were doable financial literacy interventions that had lasting impacts.)

But we can give people cash. And funnily enough that is ASI house policy.