Evolution

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. http://dx.doi.org/10.1098/rspb.2019.0907 -- There is a general consensus among archaeologists that replacement of Neanderthals by anatomically modern humans in Europe occurred around 40K to 35K YBP. However, the causal mechanism for this replacement continues to be debated. Proposed models have featured either fitness advantages in favor 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 math model show that, although both fitness and drift can produce fixation, they present important differences in 1) required initial conditions, 2) reliability, 3) time to replacement, and 4) path to replacement. The empirical archeological data are more consistent with a differential fitness model. Pure drift models are too slow to achieve modern fixation in the available time (5-8K years), too uncertain about which species fixates, and wrongly predict many Neanderthal incursions into Africa.
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. http://doi.org/10.1016/j.jtbi.2016.11.017 -- 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.
Kharratzadeh, M., Montrey, M., Metz, A., & Shultz, T. R. (2015). Resolving Rogers’ paradox with specialized hybrid learners. In D. C. Noelle, R. Dale, A. S. Warlaumont, J. Yoshimi, T. Matlock, C. D. Jennings, & P. P. Maglio (Eds.), Proceedings of the 37th Annual Conference of the Cognitive Science Society (pp. 1069-1074). Austin, TX: Cognitive Science Society. -- Culture is considered an evolutionary adaptation that enhances human reproductive fitness. A common explanation is that social learning, the learning mechanism underlying cultural transmission, enhances fitness by avoiding the extra costs of individual learning. This explanation was disproved by a mathematical model of individual and social learning, showing that social learners can invade a population but do not enhance its fitness. We extend this model to include a more complex environment, limited cognitive resources, and hybrid learners that combine social and individual learning. In this extended model, we show that social learning evolves and enhances population fitness via hybrid learners capable of specializing their individual learning. 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. In our simulations, agents evolve misrepresentations of objective reality that help them 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. Results provide support for the interface theory of perception and suggest that the individual's interface can serve not only the 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. - 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. Ethnocentrism overcomes its closest competitor by exploiting humanitarian cooperation across group boundaries as world population saturates. Traitorous strategies fare even worse than selfish ones because traitors are also exploited by ethnocentrics across group boundaries. There are individual differences between evolving worlds in terms of early humanitarian competition with ethnocentrism, including some early stages of humanitarian dominance. Such variation is normally distributed and due to early, rather than later, stochastic differences in immigrant strategies. Animations of simulated worlds are available in the paper. http://jasss.soc.surrey.ac.uk/16/3/7.html
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. - Through simulations and mathematical analysis, we establish that the mechanism responsible for the evolution of cooperation is children residing close to their parents. Group tags maintain cooperation, but do not create it. pdf
Montrey, M., & Shultz, T. R. (2010). Evolution of social learning strategies. Proceedings of the Ninth IEEE International Conference on Development and Learning (pp. 95-100). Ann Arbor, MI: IEEE. - Learning based on the passing of posterior probabilities converges to the truth more quickly and reliably than does learning based on imitation and sampling from the environment; and the latter method gets closer to the truth than does pure imitation. Evolution selects these learning strategies in proportion to their success. But if the environment changes very rapidly, evolution favors the imitation-plus-reinforcement strategy over the more sophisticated posterior passing. pdf
Kaznatcheev, A., Brown, K., & Shultz, T. R. (2010). Self-esteem and the matching effect in mate selection. In S. Ohlsson & R. Catrambone (Eds.), Proceedings of the 32nd Annual Conference of the Cognitive Science Society (pp. 972-977). Austin, TX: Cognitive Science Society. - Our model accounts for the tendency to strive for an attractive partner, but end up with one who is similar in attractiveness. It also explains the increase in this similarity as the relationship matures. 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. - Ethnocentrics dominate in evolution by exploiting humanitarian cooperation as world population saturates. 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. - From a neutral start, ethnocentrism dominates over other strategies in evolution. Early in evolution, before world saturation, humanitarian strategies can compete successfully with ethnocentrics.