Aron, Arthur, and Barbara Fraley. “Relationship Closeness as Including Other in the Self: Cognitive Underpinnings and Measures.” Social Cognition 17, no. 2 (1999): 140–60. https://psycnet.apa.org/record/1999-03814-003.
Aron, Arthur, Elaine N. Aron, and Danny Smollan. “Inclusion of Other in the Self Scale and the Structure of Interpersonal Closeness.” Journal of Personality and Social Psychology 63, no. 4 (1992): 596–612. https://psycnet.apa.org/record/1993-03996-001.
Aron, Arthur, et al. “The Self-Expansion Model of Motivation and Cognition in Close Relationships.” In The Oxford Handbook of Close Relationships, edited by Jeffry Simpson and Lorne Campbell. Oxford: Oxford University Press, 2013. https://www.oxfordhandbooks.com/view/10.1093/oxfordhb/9780195398694.001.0001/oxfordhb-9780195398694-e-005.
Christakis, Nicholas A. Blueprint: The Evolutionary Origins of a Good Society. New York: Little, Brown, 2019.
Denworth, Lydia. Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond. New York: W. W. Norton, 2020.
Harman, Oren. The Price of Altruism: George Price and the Search for the Origins of Kindness. New York: W. W. Norton, 2011.
Hruschka, Daniel J. Friendship: Development, Ecology, and Evolution of a Relationship. Berkeley: University of California Press, 2010.
Jarrett, Christian. “Close Friends Become Absorbed into Our Self-Concept, Affecting Our Ability to Distinguish Their Faces from Our Own.” Research Digest (blog), August 8, 2018. https://digest.bps.org.uk/2018/08/08/close-friends-become-absorbed-into-our-self-concept-affectingour-ability-to-distinguish-their-faces-from-our-own/.
Mashek, Debra J., and Arthur Aron. Handbook of Closeness and Intimacy. Hove, UK: Psychology Press, 2004.
Mashek, Debra J., Arthur Aron, and Maria Boncimino. “Confusions of Self with Close Others.” Personality and Social Psychology Bulletin 29, no. 3 (2003): 382–92. https://pubmed.ncbi.nlm.nih.gov/15273015/.
Nehamas, Alexander. On Friendship. New York: Basic Books, 2016.
Pahl, Ray. On Friendship. New York: Polity, 2000.
Pakaluk, Michael, ed. Other Selves: Philosophers on Friendship. Cambridge, MA: Hackett, 1991.
Radiolab. “An Equation for Good.” New York Public Radio, December 14, 2010. https://www.wnycstudios.org/podcasts/radiolab/segments/103983-equation-good.
Vernon, Mark. The Meaning of Friendship. London: Palgrave Macmillan, 2010.
Wikipedia. “Altruism.” https://en.wikipedia.org/wiki/Altruism.
Wikipedia. “George R. Price.” https://en.wikipedia.org/wiki/George_R._Price.
Wikipedia. “Self-Expansion Model.” https://en.wikipedia.org/wiki/Self-expansion_model.