Co-funded conferences:

•    Conference on Cultural Evolution held in Toulouse in 2019 (full programme found here: teb2019.pdf

•    Conference on Fertility: Causes and Consequences held online in 2021 (full programme found here: teb2019.pdf

•    Conference on Production and Sharing held in Toulouse in 2022 (full programme found here: teb2022.pdf

•    Conference on Inertia in Biological and Cultural Systems held in Toulouse in 2023 (full programme found here: teb2023.pdf)

•    Conference on Inequality in Networks held in Toulouse in 2024 (full programme found here: teb2024.pdf)


Publications by PI Ingela Alger:

•    Research Theme 1: Strategic Interactions

o    Publication of pre-print:
Doing the right thing (or not) in a lemons-like situation: on the role of social preferences and Kantian moral concerns With José Ignacio Rivero-Wildemauwe.
Non-technical abstract: Experimental evidence from the past decades shows that a sizeable share of participants in laboratory experiments are not always willing to inflict a reduction in others' material payoffs in order to obtain a larger payoff. In this paper we conduct an experiment in which the instructions to participants describe the task as the sale of a "lemon" to a willing buyer: the "seller" gains from selling, while the buyer's payoff is reduced (this is reminiscent of a situation where the good has a defect, which the buyer is unaware of);  a decision to "not sell" neither increases nor decreases the payoffs of the "seller" and the "buyer". We compare the participants' decisions in this setting with decisions taken in payoff-equivalent decisions, but described in neutral terms (the decisions are called X and Y). We find that participants are more likely to select the selfish action under the market framing. Furthermore, we seek to disentangle two distinct reasons for why participants would refrain from the selfish action: a pro-social concern, (whereby the individual cares about the other's payoff) and a Kantian moral concern (whereby an individual evaluates each action in light of what their own material payoff would be if, hypothetically, the roles were reversed and the other were to select the same action). By varying the salience of the arbitrariness of the    role distribution, we arguably vary the extent to which participants' Kantian moral concerns are triggered. In accordance with this hypothesis, we find that increased salience make the participants less likely to select the selfish action.

o    Publication of pre-print:
Norms and norm change - driven by social preferences and Kantian morality With Péter Bayer.
Non-technical abstract: Norms indicate which behaviors are commonly expected and/or considered to be morally right. We propose a theoretical model of how such norms may come about and change, in a setting where a group of individuals face a collective action problem, formalized as a linear public goods game, where contributions are collectively rational but individually irrational from a purely material point of view. Each individual has (1) an idea of what is the "right thing to do"; (2) an attitude towards making a greater material sacrifice than others; (3) an attitude towards making a smaller sacrifice than others; (4) an attitude towards deviating from the "right thing to do". We show that these preferences uniquely determine each individual's thresholds for collective behavior, whereby an individual will contribute to the public good if and only if sufficiently many others do so. Depending on the importance attached to the said attitudes, some individuals, however, prefer not to contribute regardless of what the others do, while some prefer to contribute regardless of what the others do.  The latter are leaders. We show that spontaneous norm change can occur if novel information reaches some such leaders.

o    Publication of pre-print:
Does universalization ethics justify participation in large elections? With Konrad Dierks and Jean-François Laslier.
Non-technical abstract: Why do voters incur costs to participate in large elections? This paper proposes an exploratory analysis of the implications of evolutionary Kantian morality for this classical problem in the economic theory of voting: the costly participation problem.

o    Publication of article:
Proximate and ultimate drivers of norms and norm change. Current Opinion in Psychology, Vol. 60, 2024. With Sergey Gavrilets and Patrick Durkee.
Non-technical abstract: We describe a formal model of norm psychology that can be applied to better understand norm change. The model integrates several proximate drivers of normative behavior: beliefs and preferences about a) material payoffs, b) personal norms, c) peer disapproval, d) conformity, and e) authority compliance. Additionally, we review interdisciplinary research on ultimate foundations of these proximate drivers of normative behavior. Finally, we discuss opportunities for integration between the proposed formal framework and several psychological sub-fields.
 
o    Publication of article:
Estimating social preferences and Kantian morality in strategic interactions. Journal of Political Economy Microeconomics.,Vol. 2, 2024, 665-706. [Lead article] With Boris van Leeuwen.
Non-technical summary: Recent theoretical work suggests that a form of Kantian morality has evolutionary foundations. To investigate the relative importance of Kantian morality and social preferences, such as altruism and inequity aversion, we run laboratory experiments on strategic interaction in social dilemmas. Using a structural model, we estimate social preferences and morality concerns both at the individual level and the aggregate level. We observe considerable heterogeneity in social preferences and Kantian morality. Analysis shows that the subject pool is well described as consisting of two types. One exhibits a combination of inequity aversion and Kantian morality, while the other combines spite and Kantian morality.

o    Publication of article:
Evolution of semi-Kantian preferences in two-player assortative interactions with complete and incomplete information and plasticity Dynamic Games and Applications, Vol. 13, 2023, 1288-1319. With Laurent Lehmann.
Non-technical abstract: Previous work (Alger and Weibull, 2013, 2016) shows that Homo moralis preferences with a certain degree of morality are evolutionarily stable, in the sense that once a population consists almost entirely of individuals with such preferences, no other preferences (from with the set of all continuous utility functions) can displace them. This previous work considered populations in which individuals interact without being able to observe each other's preferences (i.e., under incomplete information). Here, we focus on the class of Homo moralis preferences (referred to as semi-Kantian) and examine two notions of evolutionary viability of the value of the degree of morality: evolutionary stability, and convergence stability, where the latter means that a population that has reached a state in which all individuals have a degree of morality close to the evolutionarily stable one, selection pressure will eventually lead to the evolutionarily stable one. We do this in three distinct scenarios: (a) incomplete information; (b) complete information and incomplete plasticity (interacting individuals can observe each other's preferences, but an individual's preferences cannot be conditioned on the other's preferences); and (c) complete information and complete plasticity (interacting individuals can observe each other's preferences, and an individual's preferences may depend on the other's preferences).

o    Publication of article:
Evolutionarily stable preferences Philosophical Transactions of the Royal Society B, Vol. 378, 2023, 20210505.
Non-technical abstract: The 50-year old definition of an evolutionarily stable strategy (ESS) provided a key tool for theorists to model ultimate drivers of behavior in social interactions. For decades economists ignored ultimate drivers and used models in which individuals choose strategies based on their preferences—a proximate mechanism for behavior, taken to be fixed and given. This article summarizes some key findings in the literature on evolutionarily stable preferences, which in the past three decades has proposed models that combine the two approaches: individuals inherit their preferences, the preferences determine their strategy choices, which in turn determines evolutionary success. One objective is to highlight complementarities and potential avenues for future collaboration between biologists and economists.

o    Publication of article:
Evolution and Kantian morality: a correction and addendum.  Games and Economic Behavior, Vol. 140, 2023, 585-587. With Jörgen W. Weibull.
Non-technical abstract: In this note we correct a mistake found in our earlier paper Alger and Weibull (Games and Economic Behavior, 2016) (the mistake consisted in using a definition that assumed equilibrium existence, while not guaranteeing  such existence). As a by-product, we also obtain an extension of a result found in Alger and Weibull (Econometrica, 2013).

o    Publication of article:
Homo moralis goes to the voting booth: coordination and information aggregation. Journal of Theoretical Politics Vol. 34, 2022, 280-312. With Jean-François Laslier.
Non-technical summary: In previous work together with Jörgen Weibull, I showed that evolutionary forces should be expected to support the prevalence of a particular form of Kantian concern, which in interactions within large populations can be interpreted as partial universalization: an individual with such concerns evaluates action choices in the light of what his or her material payoff would be if, hypothetically, a share of the others were to use the same action as him/her. In this paper we take this partial universalization as a given, and revisit two classical problems in the theory of voting: the divided majority problem and the strategic revelation of information by majority vote. It is shown that, compared to electorates consisting of purely self-interested voters, such partial universalization helps voters solve coordination problems and improves  their ability to aggregate information in an efficient manner, as conjectured by Condorcet

o    Publication of article:
Evolution of preferences in group-structured populations: genes, guns, and culture. Journal of Economic Theory Vol.185, 2020, 104951. With Jörgen W. Weibull and Laurent Lehmann.
Non-technical summary: Although moral values have been part of human thinking for thousands of years, economists have tended to disregard this. Our model examines the evolutionary foundations of moral values. It leads to two main results. First, when individuals reflect on the consequences of their actions on fitnesses, a combination of self-interest and a particular kind of Kantian moral (non-consequentialistic) concern is shown to be compatible with natural selection.  Second, when individuals reflect on the consequences of their actions on material payoffs, a combination of self-interest, a (non-consequentialistic) Kantian moral concern, and a (consequentialistic) concern about the others' material payoffs is shown to be compatible with natural selection. The (consequentialistic) concern may be either pro-social (altruism) or anti-social (spite). The article builds on our earlier work (see the article published in Evolution in 2015). It combines the “island model”, a classic model used by evolutionary biologists to study the effects of population structure, with game theory and classic models of preference evolution in economics, to examine which preferences cannot be displaced by other strategies once they have become prevalent in a population.


•    Research Theme 2: The Human Family

o    Publication of article:
The evolution of early hominin food production and sharing Proceedings of the National Academy of Sciences, Vol. 120 (25), 2023, e2218096120. With Slimane Dridi, Jonathan Stieglitz, and Michael Wilson.
Non-technical abstract: Human foragers share plant and animal foods extensively. Influential scenarios for the evolution of hominin food sharing focus on either scavenging, hunting, or cooking. However, evidence of extractive foraging for nutrient-dense plant foods millions of years before the emergence of these activities suggests food sharing potentially emerged earlier. We present a novel conceptual and mathematical model of the evolution of food production and sharing in early hominins across diverse mating systems. Male mate guarding protects females from food theft, permitting females to increase extractive foraging time and efficiency. Increased efficiency motivates females to share food with males when pair bonds exist. Female provisioning of males may have catalyzed the evolution of uniquely hominin traits prior to dietary reliance on meat.

o    Publication of article:
Evolution of the Family: Theory and Implications for Economics In Oxford Research Encyclopedia of Economics and Finance, November 2019. Oxford University Press. With Donald Cox.
Non-technical summary: Which parent can be expected to be more altruistic toward their child, the mother or father? All else equal, can we expect older generation members to be more solicitous of younger family members or vice versa? Policy interventions often target recipients by demographic status: more money being put in the hands of mothers, say, or transfers of income from young to old via public pensions. Economics makes predictions about pecuniary incentives and behaviour, but tends to be agnostic about how, say, a post-menopausal grandmother might behave, just because she is a post-menopausal grandmother. Evolutionary theory fills this gap by analysing how preferences of family members emerge from the Darwinian exigencies of “survive and reproduce.” Coin of the realm is so-called “inclusive fitness,” reproductive success of oneself plus that of relatives, weighted by closeness of the relationship. Appending basic biological traits onto considerations of inclusive fitness generates predictions about preferences of family members. A post-menopausal grandmother with a daughter just starting a family is predicted to care more about her daughter than the daughter cares about her, for example. Evolutionary theory predicts that mothers tend to be more altruistic toward children than fathers, and that close relatives would be inclined to provide more support to one another than distant relatives. An original case study is provided, which explains the puzzle of diverging marriage rates by education in terms of heterogeneity in preferences for commitment. Economists are justifiably loathe to invoke preferences to explain trends, since preference-based explanations can be concocted to explain just about anything. But the evolutionary approach does not permit just any invocation of preferences. The dictates of “survive and reproduce” sharply circumscribe the kinds of preference-related arguments that are admissible.

o    Publication of article:
Paternal provisioning results from ecological change. Proceedings of the National Academy of Sciences, Vol.117, 2020, 10746-10754. With Donald Cox, Paul Hooper, Hillard Kaplan, and Jonathan Stieglitz.
Non-technical summary: Paternal provisioning is ubiquitous in human subsistence societies and unique among apes. How could paternal provisioning have emerged from promiscuous or polygynous mating systems that characterize other apes? An anomalous provisioning male would encounter a social dilemma: Since this investment in prospective offspring can be expropriated by other males, this investment is unlikely to increase the provisioner’s fitness. We present an ecological theory of the evolution of human paternal investment. Ecological change favoring reliance on energetically rich, difficult-to-acquire resources increases payoffs to paternal provisioning due to female–male and/or male–male complementarities. Paternal provisioning becomes a viable reproductive strategy when complementarities are strong, even under high paternity uncertainty. This model illuminates additional paths for understanding the evolution of fatherhood.

o    Publication of article:
On the evolution of male competitiveness. Journal of Economic Behavior and Organization Vol. 190, 2021, 228-254.
Non-technical summary: Why are some societies monogamous and others polygynous? Most theories of polygyny invoke male heterogeneity as an explanation. Arguing that such heterogeneity depends on men’s willingness to compete against each other in the first place, I propose an evolutionary game to model the evolution of this trait. Lack of competitiveness (and the associated monogamous unions) is shown to be compatible with evolution if male reproductive success decreases with the number of wives. In a model where the man and his spouse(s) make fertility and child care choices that aim at maximizing reproductive success, I show that, due to men’s involvement in child care and female agency over her fertility, male reproductive success is indeed decreasing in the number of wives under certain conditions, while it is increasing under other condition The model thus sheds light on the variation in polygyny rates across space and time in human societies.


Publications by other team members:

o    Publication of article:
Moral preferences in bargaining. Economic Theory  doi.org/10.1007/s00199-023-01544-7. By Pau Juan-Bartroli and Emin Karagözoglu.
Abstract:
We analyze the equilibrium of a bilateral bargaining game (Nash, 1953, Economet- rica, 21: 128–140). where at least one of the individuals has a preference for morality (homo moralis). We show that the equilibrium set crucially depends on these moral preferences. Furthermore, our comparative static analyses provide insights into the dis- tributional implications of individuals’ moral concerns and the composition of society. A comparison of the set of equilibria in our model with those under selfish preferences, Kantian equilibrium, fairness preferences, altruistic preferences, and inequality averse preferences reveals important differences.

o    Publication of pre-print:
A foundation for universalisation in games, by Enrico Mattia Salonia.
Abstract:
Revealed preference theory equates choices with preferences over the consequences these choices induce. Nevertheless, if a decision criterion prescribes an act for reasons unrelated to its consequences, the inference drawn regarding preferences can be misleading. I study the behaviour of non-consequentialist individuals who have preferences for universalisa- tion. They choose the action that, in a counterfactual scenario where it is also chosen by everyone else, leads to their preferred consequences. I develop a model for individuals who value their choices in light of the counterfactual consequences they induce. Choices are interpreted as revealing a preference for counterfactual consequences. I impose axioms to single out the most prominent models of universalisation, compare them, highlight and ar- guably overcome their limitations. I propose a unifying model of universalisation inspired by the equal sacrifice principle.

o    Publication of pre-print:
On injunctive norms: theory and experiments, by Pau Juan-Bartroli.
Abstract:
Recent studies have shown that individuals’ behavior is sensitive to their perceptions of socially appropri- ate behavior. In this paper, I introduce a theory of injunctive norms in which individuals evaluate the social appropriateness of a given behavior using universalization reasoning. The theory allows one to compute the social appropriateness of any behavior without relying on individuals’ expectations, preferences, and actual behavior. Furthermore, it can be applied to a wide range of interactions and rationalize several observations unaccounted for by theories of social preferences. I test the theory’s predictions with evidence from past studies and new data from a lab experiment.

o    Publication of pre-print:
Taxing moral agents, by Esteban Muñoz-Sobrado.
Abstract:
Experimental and empirical findings suggest that non-pecuniary motivations play a significant role as determinants of taxpayers’ decision to comply with the tax authority and shape their perceptions and assessment of the tax code. By contrast, the canonical optimal income taxation model focuses on material sanctions as the primary motive for compliance. In this paper, I show how taxpayers equipped with semi-Kantian preferences can account for both these non-pecuniary and material motivations. I build a general model of income taxation in the presence of a public good, which agents value morally, and solve for the optimal linear and non-linear taxation problems.

o    Publication of pre-print:
Evolutionarily stable networks, by Péter Bayer.
Abstract:
This paper studies the evolution of behavior governing strategic network formation. I first propose a general framework of evolutionary selection in non-cooperative games played in heterogeneous groups under assortative matching. I show that evolution selects strate- gies that (i) execute altruistic actions towards others in the interaction group with rate of altruism equal to the rate of assortative matching and (ii) are stable against pairwise coali- tional deviations under two qualifications: pairs successfully coordinate their deviations with probability equaling the rate of assortative matching and externalities are taken into account with the same weight. I then restrict the domain of interaction games to strategic network formation and define a new stability concept for networks called ‘evolutionarily stable networks’. The concept fuses ideas of solution concepts used by evolutionary game theory and network formation games. In a game of communication, evolutionarily stable networks prescribe equal information access. In the classic co-authorship game only the least efficient network, the complete network, is evolutionarily stable. Finally, I present an evolutionary model of homophilistic network formation between identity groups and show that extreme high degrees of homophily may persist even in groups with virtually no preference for it; thus societies may struggle to eliminate segregation between identity groups despite becoming increasingly tolerant.