Analysing mobility in mediaeval England, Clark finds that people with names derived from jobs (Cook, Butler, Thatcher, and so on) were more likely to move upwards, while those with names that derive from towns (including Baskerville, Pakenham and Walton) tended to move downwards. And not much changed after the Industrial Revolution. Surnames of Oxbridge graduates in the early 1800s, for instance, were three times as common among British MPs in the late 1900s. In the United States, tax-return data for the top taxpayers was publicly reported in 1923-24. Almost a century later, people with the same surnames as those who featured on the list are three to four times more likely to be doctors or lawyers, while those with lower-status names are under-represented. People with the high-status surname Katz are 12 times more likely to be doctors and lawyers as those with the low-status surname Washington, a name commonly adopted by freed slaves. In Japan, samurai surnames date back to before the 1868 Meiji Restoration. Even today, they are over-represented at least fourfold among doctors, lawyers, professors and writers. In China, Qing surnames, over-represented among the 19th-century elite, are over-represented among today’s corporate board chairs and government officials. And in Chile, surnames that were over-represented among landowners in the 1850s are still over-represented among high-earning occupations. Strikingly, Clark finds persistence even in Sweden, one of the world’s most egalitarian societies. The 1600s and 1700s saw the creation of a set of ''noble surnames'', which today have twice their expected share of doctors, five times their share of lawyers, and three times their share of members of the top 1 per cent of income earners. This degree of persistence of status across 10 generations demonstrates the power of inherited privilege. Gregory Clark’s analysis of intergenerational mobility signals a marked shift in the way economists think about social mobility. In his 1988 presidential address to the American Economic Association, economist Gary Becker argued that ''earnings are not strongly transmitted from fathers to sons''. Four years later, economist Gary Solon showed that prior researchers had been overestimating the degree of social mobility because they were using just a single year of data.

To see how this happens, imagine a high-earning barrister who happens to take six months off work in the year of the survey. Now suppose his son becomes a high-earning barrister too. A study that used just one year of data might wrongly assume that this was a case of someone moving from rags to riches. But a study that used several years of data would see that both father and son were well off. At this point, I need to introduce a few numbers. The standard measure of mobility across generations is the ''elasticity'' of children’s earnings with respect to their parents’ earnings – in other words, how closely the former reflects the latter. Because women have tended to have much lower rates of paid work, researchers have focused on the father-son earnings. An elasticity of zero means there was no relationship between the earnings of fathers and sons, while an elasticity of one would mean a 10 per cent rise in fathers’ earnings was associated with a 10 per cent rise in sons’ earnings. The closer the elasticity gets to one, the less mobile the society. Elasticity measures aren’t confined to income. The elasticity of height, for example, is about 0.5, which means if a father is 10 centimetres taller than average, we expect his sons to be 5 centimetres taller than average. Sure, there are tall fathers with short sons (and vice versa), but basketball dads are generally taller than gymnast dads. In the case of earnings, economists’ best estimate of intergenerational elasticity went from 0.2 when they used a single year of earnings (as did the studies Gary Becker was relying on) to 0.4 when they used a few years of earnings (Gary Solon’s approach). Over the next decade, US researchers threw better and better data at the problem, and each time, they found less and less mobility. Using more than a decade of earnings data, Bhashkar Mazumder estimated in 2005 that the intergenerational earnings elasticity for the US was 0.6. That would put it higher than the father-son height elasticity. Among American sons, fathers had a larger impact on their earnings than on their stature.

Using similar techniques, researchers began estimating father-son earnings elasticities for other countries. As one survey showed, Scandinavian nations tended to be extremely mobile, with elasticities below 0.2. In Latin America, there was much less class-jumping, with elasticities over 0.5. Compared with other nations, the US is extremely immobile, a fact that Barack Obama has thankfully switched from denying (''In no other country on Earth is my story even possible'') to decrying (''It is harder today for a child born here in America to improve her station in life than it is for children in most of our wealthy allies''). In 2006, while I was working as an economist at the Australian National University, I produced the first (and so far, only) estimates of the father-son earnings elasticity in Australia, putting the intergenerational elasticity at about 0.25. This means that a 10 per cent increase in a father’s earnings translates to a 2.5 per cent increase in his son’s earnings. My estimate implied that we are more socially mobile than the US but not as mobile as Scandinavia. Looking back through the 20th century, I found no evidence that we had become markedly more or less mobile. So what does the surname approach add to our understanding of mobility? Simply put, there are two reasons for using surnames. The first is that we only have good data on earnings (from surveys or administrative records) for the relatively recent past. If we want to understand mobility in centuries past, surnames may be the best torch for seeing into an otherwise dark statistical corner. The second, more important, reason for using surnames is that they may help take out some of the transitory fluctuations. Recall how we got more precise estimates of the intergenerational earnings elasticity when we used data that smoothed out the fluctuations in an individual’s earnings over a career? Call it the ''odd year'' problem. Now, let’s think about a different problem: a family where the social status dips down for one generation before reverting to the long-term average. You might call this the ''black sheep'' problem. By looking at surnames, we are able to look not just at single father-son pairs, but also at patterns for entire lineages.

So once we take out the odd years and black sheep, how easy is it to jump between classes? Several assumptions need to be made to estimate an intergenerational elasticity from surnames. But if we accept Gregory Clark’s methodology, his results imply a very static society. For Britain, the US, India, Japan, Korea, China, Taiwan, Chile and even Sweden, he concludes that the intergenerational elasticity is between 0.7 and 0.9. This would mean that social status is at least as hereditable as height. It suggests that while the ruling class and the underclass are not permanent, they are extremely long-lasting. Erasing privilege takes not two or three generations, but 10 to 15. If you cherish the notion of a society where anyone can make it, these results are disturbing. How do we break the pattern? Part of the answer must lie in a fair tax system, a targeted social welfare system, effective early-childhood programs, and getting great teachers in front of disadvantaged classrooms. We need banks that are willing to take a chance on funding an outsider, and it doesn’t hurt to maintain a healthy Aussie scepticism about inherited privilege. Yet Clark’s results also remind policymakers that this is no easy nut to crack. Part of the transmission of social status occurs through genes. On top of this, people tend to marry those with similar levels of education; and researchers have also documented significant differences in parenting approaches among different social groups. Making the system a bit fairer is within our reach – but a complete transformation may prove elusive.

Andrew Leigh is the federal member for Fraser and the shadow assistant treasurer. His most recent book is Battlers & Billionaires: The Story of Inequality in Australia (2013). The Australian analysis that begins this article is a preliminary result of research the author is carrying out in collaboration with Gregory Clark and Mike Pottenger.

