Evolution

Montrey, M., & Shultz, T. R. (2020). The evolution of high-fidelity social learning. Proceedings of the Royal Society B: Biological Sciences, 287(20200090). - A defining feature of human culture is that knowledge and technology continually improve over time. Such cumulative cultural evolution (CCE) probably depends far more heavily on how reliably information is preserved than on how efficiently it is refined. Therefore, one possible reason that CCE appears diminished or absent in other species is that it requires accurate but specialized forms of social learning at which humans are uniquely adept. Here, we develop a Bayesian model to contrast the evolution of high-fidelity social learning, which supports CCE, against low-fidelity social learning, which does not. We find that high-fidelity transmission evolves when (1) social and (2) individual learning are inexpensive, (3) traits are complex, (4) individual learning is abundant, (5) adaptive problems are difficult and (6) behaviour is flexible. Low-fidelity transmission differs in many respects. It not only evolves when (2) individual learning is costly and (4) infrequent, but also proves more robust when (3) traits are simple and (5) adaptive problems are easy. If conditions favouring the evolution of high-fidelity transmission are stricter (3 and 5) or harder to meet (2 and 4), this could explain why social learning is common, but CCE is rare. pdf
Shultz D. R., Montrey M., & Shultz, T. R. (2019). Comparing fitness and drift explanations of Neanderthal replacement. Proceedings of the Royal Society B 286 : 20190907, 1-8. - There is a general consensus among archaeologists that replacement of Neanderthals by anatomically modern humans in Europe occurred around 40–35 ka. However, the causal mechanism for this replacement continues to be debated. Proposed models have featured either fitness advantages in favour of anatomically modern humans or invoked neutral drift under various preconditions. Searching for specific fitness advantages in the archaeological record has proven difficult, as these may be obscured, absent, or subject to interpretation. To bridge this gap, we rigorously compare the system-level properties of fitness- and drift-based explanations of Neanderthal replacement. Our stochastic simulations and analytical predictions show that, although both fitness and drift can produce replacement, they present important differences in (i) required initial conditions, (ii) reliability, (iii) time to replacement, and (iv) path to replacement (population histories). These results present useful opportunities for comparison with archaeological and genetic data. We find greater agreement between the available empirical evidence and the system-level properties of replacement by differential fitness, rather than by neutral drift. pdf
Kharratzadeh, M., Montrey, M., Metz, A., & Shultz, T. R. (2017). Specialized hybrid learners resolve Rogers’ paradox about the adaptive value of social learning. Journal of Theoretical Biology, 414(February 2017), 8–16. - Culture is considered an evolutionary adaptation that enhances reproductive fitness. A common explanation is that social learning, the learning mechanism underlying cultural transmission, enhances mean fitness by avoiding the costs of individual learning. This explanation was famously contradicted by Rogers (1988), who used a simple mathematical model to show that cheap social learning can invade a population without raising its mean fitness. He concluded that some crucial factor remained unaccounted for, which would reverse this surprising result. Here we extend this model to include a more complex environment and limited resources, where individuals cannot reliably learn everything about the environment on their own. Under such conditions, cheap social learning evolves and enhances mean fitness, via hybrid learners capable of specializing their individual learning. We then show that, while spatial or social constraints hinder the evolution of hybrid learners, a novel social learning strategy, complementary copying, can mitigate these effects. - pdf
Kaznatcheev, A., Montrey, M., & Shultz, T. R. (2014). Evolving useful delusions: Subjectively rational selfishness leads to objectively irrational cooperation. In P. Bello, M. Guarini, M. McShane, & B. Scassellati (Eds.), Proceedings of the 36th Annual Conference of the Cognitive Science Society (pp. 731-736). Austin, TX: Cognitive Science Society. - We introduce a framework within evolutionary game theory for studying the distinction between objective and subjective rationality and apply it to the evolution of cooperation on 3-regular random graphs. In our simulations, agents evolve misrepresentations of objective reality that help them to cooperate and maintain higher social welfare in the Prisoner's dilemma. These agents act rationally on their subjective representations of the world, but irrationally from the perspective of an external observer. We model misrepresentations as subjective perception of payoffs and a quasi-magical thinking bias to inference; the former is more conducive to cooperation. This highlights the importance of internal representations, not just observed behavior, in evolutionary thought. Our results provide support for the interface theory of perception and suggest that the individual's interface can serve not only that individual's aims, but also society as a whole, offering insight into social phenomena such as religion. pdf
Hartshorn, M., Kaznatcheev, A., & Shultz, T. R. (2013). The evolutionary dominance of ethnocentric cooperation. Journal of Artificial Societies and Social Simulation, 16(3), 7. - Recent agent-based computer simulations suggest that ethnocentrism, often thought to rely on complex social cognition and learning, may have arisen through biological evolution. From a random start, ethnocentric strategies dominate other possible strategies (selfish, traitorous, and humanitarian) based on cooperation or non-cooperation with in-group and out-group agents. Here we show that ethnocentrism eventually overcomes its closest competitor, humanitarianism, by exploiting humanitarian cooperation across group boundaries as world population saturates. Selfish and traitorous strategies are self-limiting because such agents do not cooperate with agents sharing the same genes. Traitorous strategies fare even worse than selfish ones because traitors are exploited by ethnocentrics across group boundaries in the same manner as humanitarians are, via unreciprocated cooperation. By tracking evolution across time, we find individual differences between evolving worlds in terms of early humanitarian competition with ethnocentrism, including early stages of humanitarian dominance. Our evidence indicates that such variation, in terms of differences between humanitarian and ethnocentric agents, is normally distributed and due to early, rather than later, stochastic differences in immigrant strategies. pdf
Kaznatcheev, A., & Shultz, T. R. (2011). Ethnocentrism maintains cooperation, but keeping one's children close fuels it. In C. Hoelscher, T. F. Shipley, & L. Carlson (Eds.), Proceedings of the 33rd Annual Conference of the Cognitive Science Society (pp. 3174- 3179). Boston, MA: Cognitive Science Society. - Ethnocentrism, commonly thought to rely on complex social cognition, can arise through biological evolution in populations with minimal cognitive abilities. In fact, ethnocentrism is considered to be one of the simplest mechanisms for establishing cooperation in the competitive environment of natural selection. Here we study a recent agent-based model. Through our simulations and analysis, we establish that the mechanism responsible for the emergence of cooperation is children residing close to their parents. Our results suggest that group tags maintain cooperation, but do not create it. We formalize this observation as the dual-direct hypothesis: ethnocentric agents dominate humanitarian agents by exploiting the unconditional cooperation of humanitarians of different tags to maintain the number of ethnocentric agents after world saturation. We affirm previous observations on the importance of world saturation, finding its drastic effect on dynamics in both spatial tagbased and tag-less models. pdf
Shultz, T. R., Hartshorn, M., & Kaznatcheev, A. (2009). Why is ethnocentrism more common than humanitarianism? In N. A. Taatgen & H. van Rijn (Eds.), Proceedings of the 31st Annual Conference of the Cognitive Science Society (pp. 2100-2105). Austin, TX: Cognitive Science Society. - A compelling agent-based computer simulation suggests that ethnocentrism, often thought to rely on complex social cognition and learning, may have arisen through biological evolution (Hammond & Axelrod, 2006). From a neutral start, ethnocentric strategies evolve to dominate other possible strategies (selfish, traitorous, and humanitarian) that differentiate patterns of cooperation with in-group and out-group agents. We present new analyses and simulations to clarify and explain this outcome by formulating and testing two hypotheses for explaining how ethnocentrism eventually dominates its closest competitor, humanitarianism. Results indicate support for the direct hypothesis that ethnocentrics exploit humanitarian cooperation along the frontiers between ethnocentric and humanitarian groups as world population saturates. We find very little support for the contrasting free-rider-suppression hypothesis that ethnocentrics are better than humanitarians at suppressing non-cooperating free riders, although both hypotheses correctly predict a close temporal relation between population saturation and ethnocentric dominance. pdf
Shultz, T. R., Hartshorn, M., & Hammond, R. A. (2008). Stages in the evolution of ethnocentrism. In B. C. Love, K. McRae, & V. M. Sloutsky (Eds.), Proceedings of the 30th Annual Conference of the Cognitive Science Society (pp. 1244-1249). Austin, TX: Cognitive Science Society. - Computer simulations suggest that agents cooperate in the Prisoner’s Dilemma game, despite the individual cost of doing so, because they have evolved to cooperate, at least with individuals of the same kind. We present new simulations indicating that, early in evolution, humanitarian strategies compete successfully with ethnocentric ones. In just over half of the simulated worlds, there was an early stage in which humanitarian strategies, involving cooperation with all agent types, dominated over other strategies. Ethnocentric strategies involving only in-group cooperation eventually dominate. pdf