Especially in relation to animal rights, the philosopher Peter Singer has written about the subject since the 1970s, and since 2017 so has the think tank Sentience Institute, part of the 21st-century effective altruism movement.
[8] Philosopher Jeff Sebo's 2025 book, The Moral Circle, argues for expanding the scope of ethics to include not only humans but also animals, insects, artificial intelligence, and microbes.
Sebo explores these ideas through case studies on captive elephants, farmed insects, and the ethical issues surrounding the creation of digital minds.
[9] The effective altruism movement, particularly the Sentience Institute, regularly discusses moral circle expansion as a part of its philosophy.
[10] Launched in 2017 as a spinoff of the Effective Altruism Foundation, the Sentience Institute describes itself as a "think tank dedicated to the expansion of humanity's moral circle.
[12] Moral circle expansion as a concept per se was developed in a 2021 paper in the journal Futures entitled "Moral Circle Expansion: A Promising Strategy to Impact the Far Future" by Sentience Institute co-founder Jacy Reese Anthis and philosopher Eze Paez.
[1] Kasperbauer and others point out that it is not entirely clear whether the actual conditions of animals used for food or scientific research are improving, despite claims that they are entering the moral circle.
[1][8] A related criticism is that religion gave some animals a protected status that they no longer have, so they have experienced moral circle contraction.
[5] Another theory is that moral circle expansion is related to climbing Maslow's hierarchy of needs and so being able to focus on others to a greater extent once more personal needs have been fulfilled.