Online Altruism Lab

Results and Discussion

I have not yet examined the behaviors of this model in detail, but the most interesting finding is certainly that the individual willingness to commit altruistic suicide can evolve quite easily.

Figures 1 and 2 show, as an example, the development of a population of potential "martyrs" from originally pure egoists.

Fig. 1: Evolution of willingness to sacrifice oneself. In the example shown, the population easily develops a mean p-sacrifice values well above the threshold. This means that agents are prepared to end up as a martyr with a probability of around 0.3 to 0.4. This simulation used the standard parameters, except that initially none of the agents were willing to sacrifice themselves (p-sacrifice=0; this is setting start-pop: zero). In our standard model, 25% of the group members (= threshold, the green line in the plot) must sacrifice themselves so that the remaining members can survive safely. If this threshold is not reached, they each die with a probability of 80% (= subT_mort).

Fig. 2: Population development. Population size (red) and number of agents with p-sacrifice values below threshold (gray) during the same simulation described in Fig. 1. After an initial phase, the population is stable and persistent, and most of the agents have p-sacrifice values equal or greater than threshold (= range between red and gray line).

Important for the development of this willingness is that if too few group members sacrifice themselves, the remaining group members have a probability of approximately 0.7 to 0.95 of dying (subT-mort = sub-threshold mortality). If the probability is less than 0.6, the willingness will not develop. If the probability approaches one, the entire population will die out.

Why this is the case remains to be investigated. But how easily altruistic suicide can develop in the model is very surprising.

Fig. 3: Evolution of willingness to commit altruistic suicide for different thresholds in the standard setup. The three curves show the mean p-sacrifice value of the population in relation to the subT-mort values for threshold values T=0.1, 0.2 and 0.3. p-sacrifice is the willingness to commit altruistic suicide and ranges from 0 (no way) to 1 (suicide in any case); it's the evolving parameter in the simulation model. subT-mort ist the mortality for each of the remaining group members, if their group doesn't make it over the threshold. The threshold (T), in turn, is the necessary proportion of suicides required for the remaining group members to survive safely. At T=0.2, for example, at least 20% of the group members must sacrifice themselves. The standard setup is a population of 16 groups of 10 members each, random start population, 4 offspring and filling only empty groups without extra migration.

References and further reading

Ackermann, M., Stecher, B., Freed, N.E., Songhet, P., Hardt, W.-D., Doebeli, M., 2008. Self-destructive cooperation mediated by phenotypic noise. Nature 454, 987–990. https://doi.org/10.1038/nature07067

Cremer, J., Melbinger, A., Wienand, K., Henriquez, T., Jung, H., Frey, E., 2019. Cooperation in Microbial Populations: Theory and Experimental Model Systems. Journal of Molecular Biology 431, 4599–4644. https://doi.org/10.1016/j.jmb.2019.09.023

Darwin, C., 1888. The descent of man: and selection in relation to sex. John Murray, Albemarle Street.

Dugatkin, L.A., 2017. The evolution of altruism. Vestn. VOGiS 21, 487–491. https://doi.org/10.18699/VJ17.267

Fletcher, J.A., Doebeli, M., 2009. A simple and general explanation for the evolution of altruism. Proc. R. Soc. B. 276, 13–19. https://doi.org/10.1098/rspb.2008.0829

Fletcher, J.A., Zwick, M., 2004. Strong altruism can evolve in randomly formed groups. Journal of Theoretical Biology 228, 303–313. https://doi.org/10.1016/j.jtbi.2004.01.004

Hamilton, W.D., 1964. The genetical evolution of social behaviour. I. Journal of Theoretical Biology 7, 1–16. https://doi.org/10.1016/0022-5193(64)90038-4

Hardin, G., The Tragedy of the Commons. Science162,1243-1248(1968). DOI:10.1126/science.162.3859.1243

Killingback, T., Bieri, J., Flatt, T., 2006. Evolution in group-structured populations can resolve the tragedy of the commons. Proc. R. Soc. B. 273, 1477–1481. https://doi.org/10.1098/rspb.2006.3476

Kropotkin, P., 1902. Mutual aid: A factor of evolution. McClure Phillips & Co.

Maynard Smith, J., Price, G. The Logic of Animal Conflict. Nature 246, 15–18 (1973). https://doi.org/10.1038/246015a0

Nowak, M.A., 2012. Evolving cooperation. J Theor Biol 299, 1–8. https://doi.org/10.1016/j.jtbi.2012.01.014

Nowak, M. A. & May, R. M., 1992. Evolutionary games and spatial chaos. Nature 359, 826–829. (doi:10.1038/ 359826a0)

Nowak, M. A., Tarnita, C. E., Antal T., 2010. Evolutionary dynamics in structured populations. Phil. Trans. R. Soc. B. 365, 19–30 (doi:10.1098/rstb.2009.0215)

Okasha, S., 2020. Biological Altruism, in: Zalta, E.N. (Ed.), The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.

Pepper, J.W., 2000. Relatedness in Trait Group Models of Social Evolution. Journal of Theoretical Biology 206, 355–368. https://doi.org/10.1006/jtbi.2000.2132

Price, G.R., 1970. Selection and Covariance. Nature 227, 520–521. https://doi.org/10.1038/227520a0

Sigmund, K., Hauert, C., 2002. Altruism. Current Biology 12, R270–R272. https://doi.org/10.1016/S0960-9822(02)00797-2

Sober, E., Wilson, D.S., 1998. Unto Others: The Evolution and Psychology of Unselfish Behavior, Emersion: Emergent Village Resources for Communities of Faith Series. Harvard University Press.

Steiner, K.F., 2021. The Good, the Bad and the Stochastic: How Living in Groups Innately Supports Cooperation. bioRxiv 2021.02.21.431661; doi: https://doi.org/10.1101/2021.02.21.431661

Steiner, K.F., 2024. Altruism pays off in group-structured populations through probable reciprocity. bioRxiv 2024.01.20.575560. doi: https://doi.org/10.1101/2024.01.20.575560

Trivers, R.L., 1971. The Evolution of Reciprocal Altruism. The Quarterly Review of Biology 46, 35–57. https://doi.org/10.1086/406755

Wilensky, U., 1999. NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University. Evanston, IL.

Wilson, D.S., 1975. A theory of group selection. Proc. Natl. Acad. Sci. U.S.A. 72, 143–146. https://doi.org/10.1073/pnas.72.1.143

Wilson, D.S., Wilson, E.O., 2008. Evolution “for the Good of the Group.” American Scientist 96, 380–389.