Multigenerational mobility: does the Son Also Rise?

The working paper below on multigenerational mobility arrives at smaller intergenerational correlations than Greg Clark obtained (e.g., 0.4 vs 0.7). I found Clark's results hard to explain, at least in genetic terms, because estimates of assortativity in mating are much lower than required.

Related posts here and here. From the second link:

Correlations as high as 0.7 -- 0.8 are implausible from genetic factors alone without highly assortative mating. Traits such as height and IQ have narrow sense heritabilities as large as h2 ~ 0.6, so fraction of variance accounted for is ~ 60%, and midparent-child correlation as high as ~ 0.8, but under even somewhat random mating the parental midpoint is significantly closer to average than the phenotype of the more exceptional parent. This would cause children to regress to the mean much faster in height and IQ than in social status as indicated in Clark's data. It's also important to note that social status itself is only imperfectly correlated to observable phenotypes such as IQ, Conscientiousness or Extraversion. See Intergenerational mobility: Bowles, Gintis, Clark for more.

Solon's results seem to be consistent with Bowles and Gintis.

What Do We Know So Far about Multigenerational Mobility?

Gary Solon
Michigan State University

Abstract
“Multigenerational mobility” refers to the associations in socioeconomic status across three or more generations. This article begins by summarizing the longstanding but recently growing empirical literature on multigenerational mobility. It then discusses multiple theoretical interpretations of the empirical patterns, including the one recently proposed in Gregory Clark’s book The Son Also Rises.


... contrary to Clark’s prediction, most group-average studies other than his own – including the surnames-based work by Chetty et al. – have estimated much smaller intergenerational associations.

Clark was recently interviewed on KQED Forum. Michael Krasny was willing to entertain Clark's Social Darwinistic perspective ;-)

The truth about social mobility

See also Not (all) in our genes?

The Truth About Social Mobility

Full audio (55 min including Q&A; video is only 22 min highlights)

Many people assume that it is much easier to move between social classes today than at any point in humankind.

However, new research from Gregory Clark, professor of economics at the University of California, Davis, reveals that mobility rates are lower than conventionally estimated and surprisingly resistant to social policies.

By tracking family names over generations to measure social mobility across periods and countries, Clark reveals that more than ever, the only sure route to success is to be born to the right parents. And so we need to come up with new ways to tackle the entrenched force of inherited advantage and avoid creating winner-take-all societies.

Speaker: Gregory Clark, professor of economics, University of California, Davis

Genetic correlation of social outcomes between relatives (Fisher 1918) tested using lineage of 400k English individuals

Greg Clark (UC Davis and London School of Economics) deserves enormous credit for producing a large multi-generational dataset which is relevant to some of the most fundamental issues in social science: inequality, economic development, social policy, wealth formation, meritocracy, and recent human evolution. If you have even a casual interest in the dynamics of human society you should study these results carefully...

See previous discussion on this blog. 

Clark recently posted this preprint on his web page. A book covering similar topics is forthcoming.

For Whom the Bell Curve Tolls: A Lineage of 400,000 English Individuals 1750-2020 shows Genetics Determines most Social Outcomes 

Gregory Clark, University of California, Davis and LSE (March 1, 2021) 

Economics, Sociology, and Anthropology are dominated by the belief that social outcomes depend mainly on parental investment and community socialization. Using a lineage of 402,000 English people 1750-2020 we test whether such mechanisms better predict outcomes than a simple additive genetics model. The genetics model predicts better in all cases except for the transmission of wealth. The high persistence of status over multiple generations, however, would require in a genetic mechanism strong genetic assortative in mating. This has been until recently believed impossible. There is however, also strong evidence consistent with just such sorting, all the way from 1837 to 2020. Thus the outcomes here are actually the product of an interesting genetics-culture combination.

The correlational results in the table below were originally deduced by Fisher under the assumption of additive genetic inheritance: h2 is heritability, m is assortativity by genotype, r assortativity by phenotype. (Assortative mating describes the tendency of husband and wife to resemble each other more than randomly chosen M-F pairs in the general population.)

Fisher, R. A. 1918. “The Correlation between Relatives on the Supposition of Mendelian Inheritance.” Transactions of the Royal Society of Edinburgh, 52: 399-433

Thanks to Clark the predictions of Fisher's models, applied to social outcomes, can now be compared directly to data through many generations and across many branches of English family trees. (Figures below from the paper.)

The additive model fits the data well, but requires high heritabilities h2 and a high level m of assortative mating. Most analysts, including myself, thought that the required values of m were implausibly large. However, using modern genomic datasets one can estimate the level of assortative mating by simply looking at the genotypes of married couples. 

From the paper:

(p.26) a recent study from the UK Biobank, which has a collection of genotypes of individuals together with measures of their social characteristics, supports the idea that there is strong genetic assortment in mating. Robinson et al. (2017) look at the phenotype and genotype correlations for a variety of traits – height, BMI, blood pressure, years of education - using data from the biobank. For most traits they find as expected that the genotype correlation between the parties is less than the phenotype correlation. But there is one notable exception. For years of education, the phenotype correlation across spouses is 0.41 (0.011 SE). However, the correlation across the same couples for the genetic predictor of educational attainment is significantly higher at 0.654 (0.014 SE) (Robinson et al., 2017, 4). Thus couples in marriage in recent years in England were sorting on the genotype as opposed to the phenotype when it comes to educational status. 

It is not mysterious how this happens. The phenotype measure here is just the number of years of education. But when couples interact they will have a much more refined sense of what the intellectual abilities of their partner are: what is their general knowledge, ability to reason about the world, and general intellectual ability. Somehow in the process of matching modern couples in England are combining based on the weighted sum of a set of variations at several hundred locations on the genome, to the point where their correlation on this measure is 0.65.

Correction: Height, Educational Attainment (EA), and cognitive ability predictors are controlled by many thousands of genetic loci, not hundreds! 

This is a 2018 talk by Clark which covers most of what is in the paper.

For out of sample validation of the Educational Attainment (EA) polygenic score, see Game Over: Genomic Prediction of Social Mobility.

 

Vacation reading: Gregory Clark's A Farewell to Alms

A Farewell to Alms: A Brief Economic History of the World



Clark's book is an ambitious look at world economic history. The first half of the book is an excellent discussion of the Malthusian trap, in which increases in standard of living only lead to increases in population, which then (over generations) lead to declines in standard of living. The only stable point of this dynamics is at subsistence-level income. I need to think more about it, but I suspect Clark overstates the case for how well the Malthusian model applied in early human history. My impression is that there were wide disparities in levels of development that can't be easily explained in that context.

The second half of the book concerns the industrial revolution, and advances his (controversial) thesis that one of the main causes for this qualitative shift in the rate of human advancement was genetic. By analyzing historical demographic data he argues that by 1800 almost all residents of England were descended from previous generations of wealthy strivers -- reproduction rates correlated highly with family wealth in the previous Malthusian era, and the wealthy literally replaced the poor over time (less favored offspring of the rich often become the poor of future generations). Therefore, traits which are positive for commerce, long term planning, wealth accumulation, market organization, etc. had become much more widespread thanks to natural selection. I find this effect plausible -- it is consistent with recent genetic data on accelerated human evolution -- but am not as convinced that it dominates over cultural factors (at least, the two would work hand in hand). His case that it was a priori likely for England to be the first to have an industrial revolution doesn't seem particularly convincing (see Kenneth Pomeranz's Great Divergence for another set of arguments based on geography and natural resources).

Clark makes the interesting connection between modern man's descent from the strivers of previous generations and the hedonic treadmill: our happiness seems to correlate more with our position relative to perceived peers than with absolute levels of wealth.

I like the following quote from the final chapter of the book. I always found it very amusing that modern economic models can't do much better than to treat technological change as an exogenous, stochastic variable. (Yes, I know about Romer and growth theory, but would lump that in the "can't do much better" category.)

God clearly created the laws of the economic world in order to have a little fun at economists' expense. In other areas of inquiry, such as the physical sciences, there has been a steady accumulation of knowledge over the past four hundred years. Earlier theories proved inadequate. But those that replaced them encompassed the earlier theories and gave practitioners greater ability to predict outcomes across a wider range of conditions. In economics, however, we see instead that our ability to describe and predict the economic world reached a peak around 1800. In the years since the Industrial Revolution there has been a progressive and continuing disengagement of economic models from any ability to predict differences of income and wealth across time and across countries and regions.

Recent evolution in humans

Did evolution stop once modern humans emerged in Africa? Or, to the contrary, did it speed up?

This question is addressed in the forthcoming book by Greg Cochran and Henry Harpending: The 10,000 Year Explosion. Harpending is an anthropogist and Cochran a physicist. Together they have produced a number of interesting research ideas in the area of human evolution (see below). I've read a pre-release draft of the book and recommend it highly. If you enjoyed Guns, Germs and Steel by Jared Diamond, then you owe it to yourself to read this book, which directly engages Diamond's thesis that geography (not DNA) is destiny.





I discussed research supporting accelerated recent human evolution by Cochran, Harpending and collaborators in an earlier post: We are all mutants now. The figure below is from a Times article by Nicholas Wade.

We are all mutants now: Some interesting new science suggests that human evolution has accelerated in the last tens of thousands of years. The study by Hawks, Wang, Cochran, Harpending and Moyzis (of UW Madison, Affymetrix, U Utah and UC Irvine) uses linkage disequilibrium tests on hapmap SNP data to determine that roughly 7% of all genes have undergone strong selection recently. The method looks for regions of DNA with similar SNP patterns. If an advantageous gene swept through a population in a relatively short time, replacing other variants, then the pattern of nucleotide polymorphisms in that area of the chromosome will be particularly uniform throughout the group. The results imply that we are all descended from mutants who, relatively recently, out-competed and replaced their contemporaries. The distribution of mutations is not uniform in different geographical populations (i.e., races). Recent evolution is causing genetic divergence, not convergence.

There is a good theoretical argument for why evolution may speed up due to population growth. Given a particular probability distribution for producing beneficial mutations, a large population implies a faster rate of incidence of such mutations. Because reproductive dynamics leads to exponential solutions (i.e., a slight increase in expected number of offspring compounds rapidly), the time required for an advantageous allele to sweep through a population only grows logarithmically with the population, while the rate of incidence grows linearly.

To elaborate on the last point, consider the set of mutations that are sufficiently advantageous that they would sweep through a population of N humans (i.e. reach fixation) in some specified period of time, such as 5000 years. If the probability of such a mutation is p, the rate of occurrence in the population is proportional to pN. Now imagine the population of the group increases to 100N. The rate of mutations is then much higher -- 100pN -- but the time necessary for fixation has only increased by the logarithm of 100 since selective advantage works exponentially: the population fraction with the mutant gene grows as exp( r t ), where r is the reproductive advantage and t is time. This rather obvious point -- that linear beats log -- suggests that the rate of evolution will speed up as population size increases. (A possible loophole is if the probability of mutations as a function of relative advantage is itself an exponential function, and falls off rapidly with increasing advantage.) If the Hawks et al. results are any guide, as many as 7% of all genes have been under intense selection in the last 10-50,000 years. (See here for another summary of the research with a nice illustration of how linkage disequilibrium arises due to favorable mutations.) Importantly, the variants that reached fixation over this period are different in different geographical regions.

Thus civilization, with its consequently larger populations supported by agriculture, enhanced rather than suppressed the rate of human evolution.

A related question is whether selection pressure remained strong after the development of civilization. Perhaps reproductive success became largely decoupled from genetic influences once humans became civilized? Not only is this implausible, but it seems to be directly contradicted by evidence. The graph below, based on English inheritance records, shows that the rich gradually out-reproduced the poor: the wealthy had more than twice as many surviving children as the poor. (Note the range of inheritances in the graph covers the middle class to moderately wealthy; the poor and very rich are not shown.) Thus, in this period of history wealth was a good proxy for reproductive success. Genes which were beneficial for the accrual of wealth (e.g., for intelligence, self-discipline, delayal of gratification, etc.) would have become more prevalent over time. In a simple population model, any lineage that remained consistently poor over a few hundred year period would contribute almost zero to today's population of Britons.



The graph is taken from this paper:

Survival of the Richest: The Malthusian Mechanism in Pre-Industrial England

GREGORY CLARK AND GILLIAN HAMILTON

Fundamental to the Malthusian model of pre-industrial society is the assumption that higher income increased reproductive success. Despite the seemingly inescapable logic of this model, its empirical support is weak. We examine the link between income and net fertility using data from wills on reproductive success, social status and income for England 1585–1638. We find that for this society, close to a Malthusian equilibrium, wealth robustly predicted reproductive success. The richest testators left twice as many children as the poorest. Consequently, in this static economy, social mobility was predominantly downwards. The result extends back to at least 1250 in England.

See also my review of Clark's A Farewell to Alms, and this video of a talk by Clark. When Clark wrote the book he wasn't sure whether it was genetic change or cultural change that led to the industrial revolution in England. In the video lecture he comments that he has since become convinced it was largely genetic. That doesn't jibe with the back of the envelope calculation I give below -- even in the optimistic case (largest effect) it would seem to take a thousand years to have a big shift in overall population characteristics.

Here's a very crude back of the envelope calculation: if, in a brutal Malthusian setting, the top 10% in wealth were to out-reproduce the average by 20% per generation, then after only 10 generations or so (say 2-300 years), essentially everyone in the population would trace their heritage in some way to this group. In our population the average IQ of the high income group is about +.5 SD relative to the average. If the heritability of IQ is .5, then in an ideal case we could see a selection-driven increase of +.25 SD every 2-300 years, or +1 SD per millenium. This is highly speculative, of course, and oversimplified, but it shows that there is (plausibly) no shortage of selection pressure to drive noticeable, even dramatic, change. If the estimate is too high by an order of magnitude (the rich group doesn't directly replace the others; there is inevitably a lot of intermarriage between descendants of the rich and non-rich), a change of +1 SD per 10,000 years would still be possible. There's clearly no shortage in genetic variation affecting intelligence: we see 1 SD variations not just within populations but commonly in individual families!


So where does this leave us?

1) The rate of positive mutations went up due to population growth. More importantly, the rate of mutations that were likely to sweep the entire population in a fixed period of time probably went up.

2) Natural selection did not abate: there is evidence for differential reproductive rates that are impacted by genes.

3) Humans living today are possibly quite different from our ancestors of 50,000 years ago. I would guess we are smarter and better suited to living in a complex society that requires cooperation and planning. We are also probably more likely to be lactose tolerant, nearsighted and bad at hunting ;-)

Cochran and Harpending's new book deserves wide attention and serious discussion.

Demography and fast evolution

In an earlier post I discussed the population history uncovered by Gregory Clark in his book A Farewell to Alms. By examining British wills, he showed that the rich literally replaced (outreproduced) the poor over a period of several centuries.



The excerpt below is from a review of Greg Clark's book. The review is mostly negative about Clark's big picture conclusions, but does provide some interesting historical information. Note, the reviewer does not seem to understand population genetics (see discussion further below).

The comparison of Beijing nobility and Liaoning peasants is drawn from Lee and Wang’s (1999) survey of Chinese demography, which, in turn, is based on a very detailed investigation of population in Liaoning by Lee and Campbell (1997). In Liaoning, all men had military obligations and were enumerated in the so-called banner roles, which described their families in detail. Individuals’ occupations were also noted, so that fertility can be compared across occupational groups. High status, high income occupations had the most surviving sons: for instance, soldiers aged 46–50 had on average 2.57 surviving sons, artisans had 2.42 sons, and officials had 2.17 sons. In contrast, men aged 46–50 who were commoners had only 1.55 sons on average.

The references cited are

Lee, James Z., and Cameron D. Campbell. 1997. Fate and Fortune in Rural China: Social Organization and Population Behavior in Liaoning 1774–1873. Cambridge and New York: Cambridge University Press.

Lee, James Z., and Feng Wang. 1999. One Quarter of Humanity: Malthusian Mythology and Chinese Realities, 1700–2000. Cambridge and London: Harvard University Press.

So we have at least two documented cases of the descendants of the rich replacing the poor over an extended period of time. My guess is that this kind of population dynamics was quite common in the past. (Today we see the opposite pattern!) Could this type of natural selection lead to changes in quantitative, heritable traits over a relatively short period of time?

Consider the following simple model, where X is a heritable trait such as intelligence or conscientiousness or even height. Suppose that X has narrow sense heritability of one half. Divide the population into 3 groups:

Group 1 bottom 1/6 in X; < 1 SD below average
Group 2 middle 2/3 in X; between -1 and +1 SD
Group 3 highest 1/6 in X; > 1 SD above average

Suppose that Group 3 has a reproductive rate which is 10% higher than Group 2, whereas Group 1 reproduces at a 10% lower rate than Group 2. A relatively weak correlation between X and material wealth could produce this effect, given the demographic data above (the rich outreproduced the poor almost 2 to 1!). Now we can calculate the change in population mean for X over a single generation. In units of SDs, the mean changes by roughly 1/6 ( .1 + .1) 1/2 or about .02 SD. (I assumed assortative mating by group.) Thus it would take roughly 50 generations, or 1k years, under such conditions for the population to experience a 1 SD shift in X.

If you weaken the correlation between X and reproduction rate, or relax the assortative mating assumption, you get a longer timescale. But it's certainly plausible that 10,000 years is more than enough for this kind of evolution. For example, we might expect that the advent of agriculture over such timescales changed humans significantly from their previous hunter gatherer ancestors.

This model is overly simple, and the assumptions are speculative. Nevertheless, it addresses some deep questions about human evolution: How fast did it happen? How different are we from humans who lived a few or ten thousand years ago? Did different populations experience different selection pressures? Amazingly, we may be able to answer some of these questions in the near future.

Thanks to Henry Harpending for reminding me about the Chinese data and about the question of fastest plausible evolution for a quantitative trait.

Greg Clark: Genetics and Social Mobility — Manifold Episode #14

 

Gregory Clark is Distinguished Professor of Economics at UC-Davis. He is an editor of the European Review of Economic History, chair of the steering committee of the All-UC Group in Economic History, and a Research Associate of the Center for Poverty Research at Davis. He was educated at Cambridge University and received a PhD from Harvard University. His areas of research are long-term economic growth, the wealth of nations, economic history, and social mobility. 

Steve and Greg discuss: 

0:00 Introduction 

2:31 Background in economics and genetics 

10:25 The role of genetics in determining social outcomes 

16:27 Measuring social status through marriage and occupation 

36:15 Assortative mating and the industrial revolution 

49:38 Criticisms of empirical data, engagement on genetics and economic history 

1:12:12 Heckman and Landerso study of social mobility in US vs Denmark 

1:24:32 Predicting cognitive traits 

1:33:26 Assortative mating and increase in population variance 

Links: 

For Whom the Bell Curve Tolls: A Lineage of 400,000 English Individuals 1750-2020 shows Genetics Determines most Social Outcomes http://faculty.econ.ucdavis.edu/faculty/gclark/ClarkGlasgow2021.pdf 

Further discussion: https://infoproc.blogspot.com/2021/03/genetic-correlation-of-social-outcomes.html 

A Farewell to Alms: A Brief Economic History of the World https://en.wikipedia.org/wiki/A_Farewell_to_Alms 

The Son Also Rises https://en.wikipedia.org/wiki/The_Son_Also_Rises_(book)

Transcript.

Social Darwinism: 21st century edition

This is a nice summary of economic historian Gregory Clark's views on recent human evolution. See related posts. I think one standard deviation of change in population averages is possible over 1000 years, given plausible values of heritability and correlation between reproductive success and quantitative trait values.

Clark makes a good case (please follow the link and read the paper!). Will modern research rehabilitate the old Social Darwinist ideas of the 19th century?

The Domestication of Man: The Social Implications of Darwin

... Until recently, however, the one creature in the modern farmyard that was believed to be unchanged from Paleolithic times was man himself. We are assumed to still remain in our original wild form. “Our modern skulls house a stone age mind”1. For humans the Darwinian era was presumed to have ended with the Neolithic Revolution. Based on ethnographies of modern forager societies, at the dawn of the settled agrarian era people were impulsive, violent, innumerate, and lazy. Abstract reasoning abilities were limited. If we are biologically identical with these populations then only the thin patina of civilization separates us from the underlying violence and impulsivity of human nature. Scratch away that restraint and we would revert to our natural passions.

In my recent book, A Farewell to Alms: A Brief Economic History of the World I argue two things. First that all societies remained in a state I label the “Malthusian economy” up until the onset of the Industrial Revolution around 1800. In that state crucially the economic laws governing all human societies before 1800 were those that govern all animal societies. Second that was thus subject to natural selection throughout the Malthusian era, even after the arrival of settled agrarian societies with the Neolithic Revolution.

The Darwinian struggle that shaped human nature did not end with the Neolithic Revolution but continued right up until the Industrial Revolution. But the arrival of settled agriculture and stable property rights set natural selection on a very different course. It created an accelerated period of evolution, rewarding with reproductive success a new repertoire of human behaviors – patience, self-control, passivity, and hard work – which consequently spread widely.

And we see in England, from at least 1250, that the kind of people who succeeded in the economic system – who accumulated assets, got skills, got literacy – increased their representation in each generation. Through the long agrarian passage leading up to the Industrial Revolution man was becoming biologically more adapted to the modern economic world. Modern people are thus in part a creation of the market economies that emerged with the Neolithic Revolution. Just as people shaped economies, the pre-industrial economy shaped people. This has left the people of long settled agrarian societies substantially different now from our hunter gatherer ancestors, in terms of culture, and likely also in terms of biology. We are also presumably equivalently different from groups like Australian Aboriginals that never experience the Neolithic Revolution before the arrival of the English settlers in 1788.

The argument here thus unites the doctrines of Malthus and Darwin in studying human history. This is intellectually satisfying since Charles Darwin himself proclaimed his inspiration for On the Origin of Species was Malthus’s On a Principle of Population. ...

Mamet on Asperger's, Ashkenazim and the movies

The excerpt below is from his book Bambi vs Godzilla. Is he talking about movie directors, or physicists? :-)

Trivia question: what do David Mamet, Greg Cochran, Steve Pinker and Gregory Clark (author of A Farewell to Alms) have in common?

Glengarry Glen Ross is one of my favorite movies; the scene below is an all time classic. PUT THAT COFFEE DOWN!

DAVID MAMET

I think it is not impossible that Asperger’s syndrome helped make the movies.

The symptoms of this developmental disorder include early precocity, a great ability to maintain masses of information, a lack of ability to mix with groups in age-appropriate ways, ignorance of or indifference to social norms, high intelligence and difficulty with transitions, married to a preternatural ability to concentrate on the minutiae of the task at hand.

This sounds to me like a job description for a movie director. Let me also note that Asperger’s syndrome has its highest prevalence among Ashkenazi Jews and their descendants. For those who have not been paying attention, this group constitutes, and has constituted since its earliest days, the bulk of America’s movie directors and studio heads.

Neal Gabler, in his An Empire of Their Own points out that the men who made the movies – Goldwyn, Mayer, Schenck, Laemmle, Fox, - all came from a circle with Warsaw at its center, its radius a mere two hundred miles. (I will here proudly insert that my four grandparents came from that circle).

Widening our circle to all of Eastern European Jewry (the Ashkenazim), we find a list of directors beginning with Joe Sternberg’s class and continuing strong through Seven Spielberg’s and he youth of today.

...There was a lot of moosh written in the last two decades about the “blank slate”, the idea that since each child is theoretically equal under the eyes of the law, each must, by extension be equal in all things and that such a possibility could not obtain unless each child was, from birth, equally capable – environmental influences aside – of succeeding in all things.

This is a magnificent and majestic theory and would be borne by all save those who had ever had, observed, or seriously thought about children.

Races, as Steven Pinker wrote in his refutational The Blank Slate, are just rather large families; families share genes and thus, genetic disposition. Such may influence the gene holders (or individuals) much, some, or not at all. The possibility exists, however, that a family passing down the gene for great hand-eye coordination is likely to turn out more athletes than without. The family possessing the genes for visual acuity will likely produce good hunters, whose skill will provide nourishment. The families of the good hunters will prosper and intermarry, thus strengthening the genetic disposition in visual acuity.

Among the sons of Ashkenazi families nothing was more prized than genius at study and explication.

Prodigious students were identified early and nurtured – the gifted child of the poor was adopted by a rich family, which thus gained status and served the community, the religion, and the race.

The boys grew and regularly married into the family or extended family of the wealthy. The precocious ate better and thus lived longer, and so were more likely to mate and pass on their genes.

These students grew into acclaimed rabbis and Hassidic masters, and founded generations of rabbis; the progeny of these rabbinic courts intermarried, as does any royalty, and that is my amateur Mendelian explication of the prevalence of Asperger’s syndrome in the Ashkenazi.

What were the traits indicating the nascent prodigy? Ability to retain and correlate vast amounts of information, a lack of desire (or ability) for normal social interaction, idiosyncrasy, preternatural ability for immersion in minutiae; ecco, six hundred years of Polish rabbis and one hundred of their genetic descendants, American film directors.