-

In this thesis, I use an experimental model to investigate the role of social pressures in stimulating language divergence. Research into the evolution of cooperation has emphasised the usefulness of ingroup markers for swiftly identifying outsiders, who pose a threat to cooperative networks. Mechanisms for avoiding cheats and freeriders, which tend to rely on reputation, or on (explicit and implicit) contracts between individuals, are considerably less effective against short-term visitors. Outsiders, moreover, may behave according to different social norms, which may adversely affect cooperative interactions with them. There are many sources of markers by which insiders and outsiders can be distinguished, but language is a particularly impressive one. If human beings exploit linguistic variation for this purpose, we might expect the exploitation to have an influence on the cultural evolution of language, and to be involved in language divergence, since it introduces a selective pressure, by which linguistic variants are selected on the basis of their social significance. However, there is also a neutral, mechanistic model of dialect formation that relies on unconscious accommodation between interlocutors, coupled with variation in the frequency of interaction, to account for divergence. In studies of real-world communities, these factors are difficult to tease apart. The model described in this thesis put real speakers in the artificial environment of a computer game. A game consisted of a series of rounds in which players were paired up with each other in a pseudo-random order. During a round, pairs of players exchanged typed messages in a highly restricted artificial "alien language". Each player began the game with a certain number of points, distributed between various resources, and the purpose of sending messages was to negotiate to exchange these resources. Any points given away were worth double to the receiver, so, by exchanging resources, players could accumulate points for their team. However, the pairings were anonymous: until the end of a round, players were not told who they had been paired with. This basic paradigm allowed the investigation of the major factors influencing language divergence, as well as the small-scale individual strategies that contribute to it. Two major factors were manipulated: frequency of interaction and competitiveness. In one condition, all players in a game were working together; in another condition, players were put into teams, such that giving away resources to teammates was advantageous, but giving them to opponents was not. This put a pressure on players to use variation in the alien language to mark identity. A combination of this pressure and a minimum level of interaction between teammates was found to be sufficient for the alien language to diverge into "dialects". Neither factor was sufficient on its own. The results of these experiments suggest that a pressure for the socially based selection of linguistic variants can lead to divergence in a very short time, given sufficient levels of interaction between members of a group.

Evolutionary game theory tries to explain the emergence of stable behaviors observed in human and animal societies. Prominent examples of such behaviors are cooperative and conformist behaviors. In the first part of the thesis, we develop a model of indirect reciprocity with institutional screening to study how institutions may promote cooperative behavior. We show that cooperation can emerge if screening institutions are sufficiently reliable at identifying cooperators. The second part presents a large-population learning model in which individuals update their beliefs through time. In the model, only one individual updates his beliefs each period. We show that a population, playing a game with two strategies, eventually learns to play a Nash equilibrium. We focus on coordination games and prove that a unique behavior arises both when players use myopic and perturbed best replies. The third part studies the payoff calculation in an evolutionary setting. By introducing mutual consent as a requirement for game play, we provide a more realistic alternative way to compute payoffs. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.</p>

It is well known that in contrast to the Prisoner's Dilemma, the snowdrift game can lead to a stable coexistence of cooperators and cheaters. Recent theoretical evidence on the snowdrift game suggests that gradual evolution for individuals choosing to contribute in continuous degrees can result in the social diversification to a 100% contribution and 0% contribution through so-called evolutionary branching. Until now, however, game-theoretical studies have shed little light on the evolutionary dynamics and consequences of the loss of diversity in strategy. Here, we analyze continuous snowdrift games with quadratic payoff functions in dimorphic populations. Subsequently, conditions are clarified under which gradual evolution can lead a population consisting of those with 100% contribution and those with 0% contribution to merge into one species with an intermediate contribution level. The key finding is that the continuous snowdrift game is more likely to lead to assimilation of different cooperation levels rather than maintenance of diversity. Importantly, this implies that allowing the gradual evolution of cooperative behavior can facilitate social inequity aversion in joint ventures that otherwise could cause conflicts that are based on commonly accepted notions of fairness. (authors' abstract)

Uma das características que nos distinguem de outros seres vivos é nossa cultura. Entretanto, como comportamentos não fossilizam, é difícil reconstruir o passado para gerar insights sobre por que nos tornamos o que somos hoje. Juntamente com dados etnográficos e experimentais, os modelos matemáticos têm sido utilizados para abordar a questão sobre como nossos comportamentos foram moldados pela evolução. Esta tese está dividida em duas partes. Na primeira parte, discutiremos sobre seleção multinível e sobre como o framework matemático chamado Two-level Fisher Wright (TLFW) pode nos ajudar a entender a evolução da cooperação em populações humanas. Após descrevermos o problema da cooperação através do uso de ferramentas de teoria dos jogos, revisamos algumas das teorias atuais sobre por que a cooperação evoluiu. Em seguida, empregamos o framework TLFW ao problema da emergência de altruísmo em populações de caçadores-coletores, considerando uma situação em que o conflito entre grupos direciona a seleção. Na segunda parte, abordamos o tópico de diversidade linguística e apresentamos a importância de se estudar a competição entre línguas para ajudar a preservá-las. Traçando um paralelo entre a evolução das línguas e a evolução de normas sociais, introduzimos um modelo para analisar a persistência de dialetos, quando existe competição com uma língua padrão nacional. / One of the features that distinguish human beings from other living species is our culture. However, since behaviors do not fossilize, it is difficult to reconstruct the past to get insights about why we are who we are. Along with ethnographic and experimental data, mathematical models have been used to address the question of how our behaviors were shaped by evolution. This thesis is divided into two parts. In the first part, we will discuss multilevel selection and how the mathematical framework Two-Level Fisher-Wright (TLFW) can help us to understand the evolution of cooperation in human populations. After describing the problem of cooperation by using game theory, we review some of the present theories about why cooperation has evolved. Then, we apply the TLFW framework to the problem of the evolution of altruism in populations of hunter-gatherers, considering a situation in which group conflict drives selection. In the second part, we discuss language diversity and present the importance of studying the competition between languages for helping to preserve them. By drawing a parallel between the evolution of language and social norms, we introduce a mathematical model to analyze the persistence of dialects competing against a national standard language.

Uma das características que nos distinguem de outros seres vivos é nossa cultura. Entretanto, como comportamentos não fossilizam, é difícil reconstruir o passado para gerar insights sobre por que nos tornamos o que somos hoje. Juntamente com dados etnográficos e experimentais, os modelos matemáticos têm sido utilizados para abordar a questão sobre como nossos comportamentos foram moldados pela evolução. Esta tese está dividida em duas partes. Na primeira parte, discutiremos sobre seleção multinível e sobre como o framework matemático chamado Two-level Fisher Wright (TLFW) pode nos ajudar a entender a evolução da cooperação em populações humanas. Após descrevermos o problema da cooperação através do uso de ferramentas de teoria dos jogos, revisamos algumas das teorias atuais sobre por que a cooperação evoluiu. Em seguida, empregamos o framework TLFW ao problema da emergência de altruísmo em populações de caçadores-coletores, considerando uma situação em que o conflito entre grupos direciona a seleção. Na segunda parte, abordamos o tópico de diversidade linguística e apresentamos a importância de se estudar a competição entre línguas para ajudar a preservá-las. Traçando um paralelo entre a evolução das línguas e a evolução de normas sociais, introduzimos um modelo para analisar a persistência de dialetos, quando existe competição com uma língua padrão nacional. / One of the features that distinguish human beings from other living species is our culture. However, since behaviors do not fossilize, it is difficult to reconstruct the past to get insights about why we are who we are. Along with ethnographic and experimental data, mathematical models have been used to address the question of how our behaviors were shaped by evolution. This thesis is divided into two parts. In the first part, we will discuss multilevel selection and how the mathematical framework Two-Level Fisher-Wright (TLFW) can help us to understand the evolution of cooperation in human populations. After describing the problem of cooperation by using game theory, we review some of the present theories about why cooperation has evolved. Then, we apply the TLFW framework to the problem of the evolution of altruism in populations of hunter-gatherers, considering a situation in which group conflict drives selection. In the second part, we discuss language diversity and present the importance of studying the competition between languages for helping to preserve them. By drawing a parallel between the evolution of language and social norms, we introduce a mathematical model to analyze the persistence of dialects competing against a national standard language.

Network reciprocity describes the emergence of cooperative behaviour where interactions are constrained by incomplete network connectivity. It has been widely studied as an enabling mechanism for the emergence of cooperation and may be of particular interest in explaining cooperative behaviours amongst unrelated individuals or in organisms of lower cognitive abilities. Research in this area has been galvanised by the finding that heterogeneous topology promotes cooperation. Consequently there has been a strong focus on scale-free networks; however, such networks typically presuppose formative mechanisms based on preferential attachment, a process which has no general explanation. This assumption may give rise to models of cooperation that implicitly encode capabilities only generally found in more complex forms of life, thus constraining their relevance with regards to the real world. By considering the connectivity of populations to be dynamic, rather than fixed, cooperation can exist at lower levels of heterogeneity. This thesis demonstrates that a model of network fluctuation, based on random rather than preferential growth, supports cooperative behaviour in simulated social networks of only moderate heterogeneity, thus overcoming difficulties associated with explanations based on scale-free networks. In addition to illustrating the emergence and persistence of cooperation in existing networks, we also demonstrate how cooperation may evolve in networks during their growth. In particular our model supports the emergence of cooperation in populations where it is originally absent. The combined impact of our findings increases the generality of reciprocity as an explanation for cooperation in networks.

La coopération est un comportement présent en abondance dans le vivant et central à la plupart des transitions majeures en évolution. Pourtant, son évolution est difficile à expliquer. En particulier, l'origine des comportements de coopération mutualiste, qui sont bénéfiques à tous les participants, à été peu étudiés. Dans cette thèse, nous nous intéressons au rôle de la coordination dans l'évolution de la coopération mutualiste à l'aide d'outils en robotique évolutionniste. Dans un premier temps, nous modélisons en robotique évolutionniste l'évolution de la coopération dans une tâche de chasse collective afin d'étudier l'influence des mécanismes sous-jacent aux comportements de coordination sur l'évolution de la coopération. Nous montrons notamment la nécessité d'utiliser des modèles qui considèrent les aspects plus pratiques du comportement. Dans un second temps, nous nous intéressons à la conception de robots coopératifs à l'aide de la robotique évolutionniste. Nous étudions notamment l'influence de la composition génétique des groupes de robots sur l'efficacité des comportements de coordination. Cette thèse contribue donc de deux manières différentes au sujet général de l'évolution de la coopération : par de la modélisation de problèmes biologiques et la conception de robots collectifs. / Cooperation is a behaviour that is prevalent in living beings and is central to most of the major transitions in evolution. Yet explaining its origin is a challenge. In particular, the evolution of mutualistic behaviours, where every individual benefits from this behaviour, has been relatively ignored. In this thesis, we are interested in the role of coordination in the evolution of mutualistic cooperation. To that end, we use tools from evolutionary robotics. First, we model the evolution of cooperation in a collective hunting task with evolutionary robotics. We want to study the influence of the underlying mechanisms of coordination behaviours on the evolution of cooperation. We reveal that it is necessary to consider modeling techniques that account for the more practical aspects of behaviours. Then, we are interested in the design of cooperative robots with evolutionary robotics. We study the influence of genetic team composition on the efficiency of coordination behaviours. Therefore, this thesis contributes to the general subject of the evolution of cooperation in two different manners: modeling biological problems and designing collective robots.

Cooperation presents a major challenge for evolutionary theory: how can competition favor a trait that imposes a cost on the individual expressing it while benefitting another? This challenge has been answered by theory that emphasizes the importance of assortment between individuals that tend to cooperate and those who tend to behave selfishly, or `cheat'. Microbial cooperation remains puzzling, given the generally high genetic and taxonomic diversity of most microbial communities. Many microbial populations rely on shared, beneficial extracellular products for an array of functions in nature. However, when these lineages are maintained in liquid cultures, many are invaded and outcompeted by spontaneous `cheater' mutants that forego investments in these products while benefitting from those produced by neighbors. The apparent evolutionary instability of microbial investments in extracellular products in well-mixed laboratory cultures finds a natural parallel in the phenomenon of toxic microalgal blooms. These extremely dense populations of often free-living microalgae destroy populations of competing microalgae and grazing zooplankton that normally control population densities. Bloom populations of planktonic microalgae are unstructured, and seem ill suited for the evolution of cooperation. In this thesis, I have established a new theoretical framework for understanding the evolution of microbial external goods. This framework highlights the importance of cell-level structure in the distribution of these external products, as well as genetic structuring in populations. This perspective informed an investigation into the social niche of a biofilm-dwelling regulatory mutant of the important biocontrol strain Pseudomonas chlororaphis. In the highly self-structured environment of a bacterial biofilm, a surprising mutualistic association between this mutant and the wild type emerged, underscoring the importance of microbial ecology in understanding the evolution of niche construction. Extending these lessons to the evolutionary problem of exotoxins in free-swimming microalgae yields the novel possibility that fluctuations in density of toxic strains shift a cell-level functioning exotoxin into a true public good that may be exploited by cheaters. I show that exotoxicity can serve cell-level functions in Prymnesium parvum. Despite these cell-level benefits, the existence of nontoxic lineages within toxic blooms hints at a complex interaction between rapid evolutionary and ecological changes in toxic blooms.

No description available.