I have recently made public a peer-reviewed preprint. There I talk about how events that happened to our ancestors a long time ago affect us today (intergenerational persistence).
The preprint is blowing off my charts with thousands of visits. So I thought I would share more thoughts while the iron is still hot.
In this post I write more informal comments - my personal takeaways. Take these as more informed by my intuition than by hard evidence.
You have been warned.
Intergenerational persistence is an important topic for Effective Altruism. It can help us understand how our actions today can affect people many generations later. For example, I want to know if promoting truth and cooperation today can persistently affect the values of future people.
The Forethought Foundation hired me to review seven papers on these sorts of persistent effects. These papers study things that may seem a bit... outlandish. Examples include a) the relation between the agricultural tools used by your ancestors and modern gender attitudes; b) whether descendants of Africans in places raided by slavers are less trusting; and c) whether descendants of early Catholics are more individualistic.
I'll admit it - I had a strong bias against intergenerational persistence when I started. With all due respect to my grand-grand-grand-grand-grand parents, I found it hard to believe that they have influenced me very much. So on I went, hunting for how the researchers had managed to mess it up.
After engaging with the literature, I have reluctantly changed my mind. Many papers I reviewed had some methodological issues, yes. But I also found careful, robust and reasonable analysis on some key papers. Short of manufacturing the data, I don’t see how they could have got such strongly significant results otherwise.
I now believe that there is a small degree of intergenerational persistence of values. Emphasis on small - if the effects were bigger I would have expected to see more dramatic examples in the papers.
So sorry grand-grand-grand-grand-grand mother - seems like I owe you a bit more of my heritage than I thought I did.
It is still not clear to me how the transmission actually happens. Is it because of parents teaching their children who teach their children and so on? Parents founding institutions that locked-in their values? Parents etching sternly worded reminders in family heirlooms?
Most papers I reviewed argued the transmission was primarily about parents-teaching-children. However, they rely on historical and psychological evidence I don't feel comfortable evaluating.
It is also not clear whether the persistent effects stay constant or diminish with time. I'd expect the latter - if only because I have 4 grandparents, 8 great-grandparents and 16 grand-grand-grand parents. So naively I would expect any effect to dilute with each successive generation.
My impression of the papers in a nutshell
Schulz et al paper on religion, kinship and psychological variation puts up a strong case for cultural transmission. They look at how places where the Catholic Church was established earlier are WEIRDer (particularly, more individualistic). But as the authors point out we are not sure of the causal mechanism. It likely has something to do with religion and how families are structured. But the data studied in the paper is not enough to tell whether the correlation is causal.
Nunn’s previous work on slavery and economic variation is suggestive. He looks at African countries that were specially affected by slavery, and finds that those countries have relatively lower GDP today. But the analysis is underpowered, the causal analysis stops being significant after controlling for precolonial prosperity and the mediation analysis is not conclusive. According to a paper cited by Nunn, slavery cut the population of Africa in half - this must have messed up economic development in all sort of ways beyond changing cultural values.
Unlike with movies, the sequel was better. Nunn and Wantchekon’s study on slavery and trust finds that descendants of people in areas of Africa that were more affected by slavery exhibit lower levels of trust. Economist Kelly Morgan pointed out that Nunn and Wantchekon's results are no longer significant if we exclude respondents in Benin, Nigeria and Ghana (which are specially low on trust and have a very slavery-intensive past). But those are 25% of the sample, which is such a large fraction that calling them outliers starts feeling more suspicious. Regardless, I could not rule out a spurious correlation.
I mostly do not trust Guiso et al’s study of the independence of medieval Italian cities and modern measures of civic capital. They look at how Italian cities that became independent city-states during medieval times donate more, are less likely to cheat on high school exams and are generally better neighbours. I was not able to find the city of origin of the researchers, so I cannot unduly accuse them of a conflict of interest here. But I can definitely bring up that their proxies for civic capital are contrived and the results are not very robust. With one exception: I could not find any issues with the results that relate medieval independence to receiving a gold medal for heroic resistance against the nazi regime in WW2. But they analyzed this outcome in less depth and with less nuance in the paper. Aside, I falsified their proposed mediation mechanism (“self-sufficiency”).
a) Jha’s paper on South Asian trade, b) Voitlander and Voth’s paper on antisemitism in Germany and c) Alesina et al’s paper on agriculture and gender all have significant weaknesses, and I would not recommend relying on them. Some problems I found with these papers are, respectively, a) non significant results on the natural experiment, b) non significant results after correcting for multiple hypothesis testing and c) a reversal of the result depending on the control for national income.
(in what I can only assume is a deliberate effort to make my life more difficult, the data for Jha's paper was not and as far as I know still is not publicly available - and Voitlander and Voth's somehow decided to use different non-standard methods for each result they present. Alesina et al’s paper was less troublesome, though they are to blame for having me google "plow hoe sex" in what must be the most naive search ever)
All in all, I would bet there are some small persistent effects
Again, emphasis on small. The causal effects identified in the papers were in the range of about 0.1 standard deviations of the outcome per standard deviation of the exposure. That is, if you worked hard to move culture in a particular direction, I would expect at most 10% of the change you bring in to persist in future generations.
It is plausible that smaller effects exist - which we would not have enough statistical power to detect. It is unlikely that stronger effects exist, since those would be easier to detect. And I would correspondingly have expected to be flooded by papers studying how your ancestors' religion explains your Netflix watching habits.
Since the effects identified are at the border of the sensitivity of our current methods, it is unclear how significant they are. Better tools and tests would help address that issue.
Lacking these future methods, we have to speculate. My guess is that there must be some small cultural parent-to-children persistence. This guess is mostly based on a hunch that the results are underpowered more than biased. Also, I see religion as a credible proof-of-concept for cultural persistence ; it is ripe with many rituals and customs that have survived through generations. Other people I have talked to have different opinions on the whole issue.
We do not know whether persistent effects tend to vanish
There just hasn’t been much research done on the topic as far as I can tell. This is a crucial question for longtermism - a sort of “discount rate” for culturally persistent interventions.
Just from looking at the seven papers I reviewed, there is no evident pattern. Maybe the variation stays the same, maybe it diminishes with time or maybe it traces a cosine wave whose oscillation period matches the lunar phases. Intuitively I would bet that it diminishes with time, but this is based on a hunch rather than hard evidence.
We do not know whether cultural persistence can be triggered on purpose
All the papers I reviewed study persistent outcomes that were not deliberately sought.
In some of those cases the changes that brought the initial variation were quite extreme - for example enslaving enough people in Africa to halve (!) the population of the continent.
Thus even if cultural persistence is possible, the events that lead to it might not be realistic to deliberately trigger in practice.
To progress, we’d need to study the cultural legacy of intentional movements. This is a much harder topic, where quantitative proxies will be hard to come by.
We need more open reviews of persistence studies papers
Not to point fingers, but as a relative outsider to the field, I was able to add significant nuance to the analyses conducted in these widely cited papers.
This points to a gap in the field around reviewing each other’s work, replicating previous work and performing more robustness checks.
Kelly’s recent work is an example of this. I expect further analysis to reveal more issues. So you know what to do if you are an econ grad student looking for something to work on.
Research on persistence is hard
There is a mixed bag of results that are plausible and results that do not hold up under scrutiny. Most of the results I looked into find a statistically significant correlation, but many of the analyses of causation and mediation are not convincing.
As a telltale sign, the results I found more convincing involved natural experiments and studying children-of-immigrants.
I was surprised to learn from Kelly's work that the slavery and trust analysis did not stand up after removing respondents from the Bight of Benin. While I think this critique does not ultimately hold water, this makes me hesitant about my results. I think that if other researchers attempted replicating them they would find more issues.
So, can we influence our great great great grandchildren's values? The answer is a very scientific and very disappointing maybe. Definitely not by much - and we have little idea of the best mechanisms for doing so. I am waiting for Kelly to publish his next paper and turn every persistence result on its heels again. Meanwhile, why not check out my full paper?
Again, I thank the Forethought Foundation for commissioning this work, and all the people who helped with the article.
Nuño Sempere reviewed a previous version of the original post I prepared for the release of the preprint, and his comments convinced me of writing a more informal post as well. Faatima Osman helped me with editing, and pointed out a critical flaw in my results. Ronja Lutz provided superb editing and feedback. I blame Kat Woods' post for all the terrible jokes I have inflicted upon you over the course of this article.