Nichols, R., Charbonneau, M., Chellappoo, A., Davis, T., Haidle, M., Kimbrough, E. O., Moll, H., Moore, R., Scott-Phillips, T., Purzycki, B. G., & Segovia-Martin, J. (2024). Cultural evolution: A review of theoretical challenges. Evolutionary Human Sciences, 6, e12. https://doi.org/10.1017/ehs.2024.2 (open access)

Eleven researchers and philosophers of cultural evolution review the theoretical problems in their own field. They were prompted by a survey in which members of the Cultural Evolution Society said the field lacked agreement on its central ideas and used its key terms too loosely to test. The paper works through what culture is taken to mean, how you decide where one culture stops and another starts, and what the field assumes about how minds work.

• The paper separates defining culture from counting cultures. Can we say where one culture ends and another begins without making an arbitrary decision? If not, what happens to research that compares them?
• The authors suggest that wanting results to generalise pushes the field towards simple, timeless theories. Is that a habit that could change, or does this way of thinking require it?
• Models of cultural transmission leave people very little room to act agentically. Is that a useful simplification or a false picture?

Kunst, J. R., & Mesoudi, A. (2025). Decoding the dynamics of cultural change: A cultural evolution approach to the psychology of acculturation. Personality and Social Psychology Review, 29, 111–144. https://doi.org/10.1177/10888683241258406

People copy the majority around them, or deliberately do the opposite…they copy those with status, or copy whatever seems to be working. The paper explains the familiar acculturation strategies as the settled result of many such choices across a population of people we identify as belonging to a “culture”. I am hoping the discussions from September about the boundaries will make us think extra hard about the issues.

• Which of the problems raised in September does this paper run into, which does it answer, and which does it leave alone?
• Acculturation is something people live through and often struggle with. What goes missing when it is described as a settled state?

Toomela, A. (2025). Quo vadis, cultural psychology? Time to become psychology. Again. Integrative Psychological and Behavioral Science, 59, article 75. https://doi.org/10.1007/s12124-025-09936-1

Toomela argues that cultural psychology has borrowed its methods from mainstream psychology and lost track of what it was meant to be studying. Working from Vygotsky and Luria, he treats culture and mind as wholes that cannot be understood by breaking them into pieces and counting. He puts three questions to any object of study: what is the whole, what are its parts, and how do the parts stand to one another. Several replies have since appeared in the same journal if you want to follow the argument further.

• Toomela says you have to decide what you are studying before you choose how to study it. Is he right, and does anyone in the field actually work that way?
• Can this approach account for cultural change as well as the population approach does?
• Are these two positions disagreeing, or answering different questions?

Brinkmann, L., et al. (2023). Machine culture. Nature Human Behaviour, 7, 1855–1868. https://doi.org/10.1038/s41562-023-01742-2

Algorithms now choose much of what people see, decide what spreads, and increasingly produce the material itself. The paper treats this as a change in how culture works and asks what follows. It also makes a good test of where we have got to. On the first view of culture, machines are already taking part. On the second, they cannot be, and something else is going on that needs a different name.

• Which view of culture does the paper assume, and would its findings still hold if you translated them into the other?
• Does something need a point of view of its own before it can have a culture?
• After four papers, do we agree on anything? If not, are we disagreeing about culture or about what counts as an explanation?

Speelman, C. P., Parker, L., Rapley, B. J., & McGann, M. (2024). Most psychological researchers assume their samples are ergodic: Evidence from a year of articles in three major journals. Collabra: Psychology, 10(1), 92888. https://doi.org/10.1525/collabra.92888 (open access)

The authors read a year of papers in three major journals and counted how many moved from an average across people to a claim about individual people. Nearly all of them did. Almost none checked whether the move was justified. The paper is not about culture, which is part of why we are reading it. The problem belongs to the discipline rather than specifically to cultural psychology.

• Is this a problem with how researchers are trained, with what journals reward, or with the questions psychology chooses to ask?
• Are there questions where an average across people is the right answer rather than a shortcut to one?
• Cultural psychology often averages to the level of a country. Is that the same mistake, just dressed up in different clothes?

Gomes, C. M. A., Jelihovschi, E. G., de Araujo, J., & Blesa Farias, H. (2025). Ergodicity and human nature: Natural incompatibility. Theory & Psychology. https://doi.org/10.1177/09593543251383517

Ergodicity is a concept created at the end of the 19th century, which defines a kind of stochastic process and is very useful in many applied sciences including human sciences. Its main premise says that population and individual averages are equal. In psychometrics, it has been common to use population average to make inferences about the measure of the individual. Indeed, this can be done, but exclusively in ergodic processes and systems. However, none of the processes involving human beings, be they mental or physical, can ever be ergodic. This problem was first highlighted by Molenaar, but later, many researchers including Molenaar began publishing about processes that could be interpreted as not fully ergodic; the literature calls this a “continuum,” as opposed to “all or nothing” which we argue is the only correct approach. We claim that a process is either ergodic or nonergodic, there is nothing in between, and that time is ripe for researchers working in all sciences related to human behavior and health to acknowledge this truth: population measures cannot be used as measures of the individual.

• Is the all-or-nothing claim forced by the mathematics, or is it a decision about how to make the case?
• If the argument holds, is existing research wrong, or is it about something other than what it says it is about?
• Does the argument rest on a claim about people, as the title suggests, or only on the maths?

Golino, H., Nesselroade, J., & Christensen, A. P. (2025). Toward a psychology of individuals: The ergodicity information index and a bottom-up approach for finding generalizations. Multivariate Behavioral Research. https://doi.org/10.1080/00273171.2025.2454901

A reply to the question that was the focus of the Gomes’ paper last time. Rather than treating the problem as all or nothing, these authors measure how much is lost when a group pattern is applied to the individuals in it, and then they group people only where the “loss” is small. Generalisations get built up from individuals instead of being assumed from the start.

• Does measuring the loss answer the February paper, or accept its point and carry on regardless?
• When similar individuals are grouped together, is that group a real thing or a convenience?
• Building up from individuals still ends in a generalisation. What makes it safe?

Lundh, L.-G. (2024). Person, population, mechanism: A rejoinder to critics and an elaboration of the three-branch model. Journal for Person-Oriented Research, 10(1), 68–84. https://doi.org/10.17505/jpor.2024.26295 (open access)

We finish the year by reflecting on what all this means for the discipline. In the paper, Lundh divides psychological research into three kinds: research on persons, on populations, and on mechanisms.

• Is research on populations psychology, or demography carried out with psychological measures?
• Does dividing the field into three branches settle the argument or make it permanent?
• Taking the whole year together: does whatever we decided culture is fit into any of Lundh’s three branches?