Moral circle expansion is the attempt to expand the perceived boundaries of the category of moral patients. It has been proposed as a priority cause area (Anthis & Paez 2021) and as a heuristic for discovering cause X (Vaughan 2016).
Aird, Michael (2020) Collection of sources relevant to moral circles, moral boundaries, or their expansion, Effective Altruism Forum, May 7.
Many additional resources on this topic or related topics.
Anthis, Jacy Reese (2018) Why I prioritize moral circle expansion over artificial intelligence alignment, Effective Altruism Forum, February 20.
Anthis, Jacy Reese & Eze Paez (2021) Moral circle expansion: A promising strategy to impact the far future, Futures, vol. 130, p. 104743.
Karnofsky, Holden (2017) Radical empathy, Open Philanthropy, February 16.
Laham, Simon M. (2009) Expanding the moral circle: inclusion and exclusion mindsets and the circle of moral regard, Journal of Experimental Social Psychology, vol. 45, pp. 250–253.
Singer, Peter (1981) The Expanding Circle: Ethics and Sociobiology, New York: Farrar, Straus and Giroux.
Slinsky, Grue (2019) The moral circle is not a circle, Effective Altruism Forum, August 14.
Section on the expanding moral circle in MacAskill, Will & Darius Meissner (2020) Introduction to Utilitarianism: An Online Textbook, Oxford.