1. Biological altruism. In E. N. Zalta (Ed.), The Stanford encyclopedia of philosophy (Summer 2020 edition). https://plato.stanford.edu/archives/sum2020/entries/altruism-biological/
2. Britannica. (2018). The editors of encyclopaedia. “Kin selection”. Encyclopedia Britannica, 14 April 2018. https://www.britannica.com/topic/kin-selection. Accessed 3 July 2022.
3. Britannica. (2022). The information architects of encyclopaedia. “Group selection”. Encyclopedia Britannica, 1 July 2022. https://www.britannica.com/facts/group-selection. Accessed 2 July 2022.
4. Feigin, S., Owens, G., & Goodyear-Smith, F. (2014). Theories of human altruism: A systematic review. Journal of Psychiatry and Brain Functions, 1, 5. https://doi.org/10.7243/2055-3447-1-5
5. Foster, R. F., Wenseleers, T., & Ratnieks, F. L. W. (2006). Kin selection is the key to altruism. Trends in Ecology and Evolution, 21(2), 57–60.