Who believed in the idea of a "state of nature" where individuals act out of self-interest?

The concept of a "state of nature" refers to a philosophical idea concerning human existence in the absence of institutional governance, where individuals act primarily based on their own self-interest. Thomas Hobbes articulated this idea in his seminal work, "Leviathan," published in 1651. He proposed that in this state, individuals would be in constant conflict for resources, leading to a life that is "solitary, poor, nasty, brutish, and short." Hobbes believed that because of this inherent self-interest and the potential for conflict, individuals would willingly surrender certain freedoms to a powerful sovereign authority in exchange for security and social order.

In contrast, John Locke viewed the state of nature more positively, believing it could be a state of peace and reason, where individuals respect each other's rights. Aristotle focused on human nature in the context of community and virtue rather than a raw self-interested perspective. Karl Marx's theories revolved around class struggles and economic systems rather than the individualistic state of nature.

Therefore, Hobbes' interpretation of the state of nature as a foundational aspect of human behavior grounded in self-interest is what distinguishes his philosophy, making him the correct answer to the question.