trolley-4
Explanation
The Joke
The comic presents a variation on the classic trolley problem -- a famous thought experiment in ethics where you must choose between letting five people die or diverting the trolley to kill one person instead. Here, a person is posed this exact dilemma, but instead of agonizing over the moral implications (as is typical in philosophy discussions), they immediately and casually choose to kill the one person, citing a completely different concern: inbreeding.
The caption reveals the twist -- "Trolley problems got a lot easier once there were only 7 people left on earth." In this post-apocalyptic scenario with only 7 humans remaining, the ethical calculus is no longer about abstract utilitarian principles. It is about raw survival math. Losing five of your seven remaining humans would be catastrophic for the species, making the "correct" answer blindingly obvious and eliminating all the philosophical hand-wringing the trolley problem is famous for.
The Humor
The humor works on multiple levels. First, it deflates the grand philosophical seriousness of the trolley problem by placing it in a context where the answer is trivially obvious -- of course you save the five when humanity is nearly extinct. Second, the respondent's specific concern about inbreeding is hilariously pragmatic; rather than mourning the loss of even one precious human, he is already thinking about the genetic viability of the remaining population. It is a wonderful collision between lofty moral philosophy and grim biological reality.
References
The trolley problem is a thought experiment in ethics first introduced by philosopher Philippa Foot in 1967 and later elaborated by Judith Jarvis Thomson. It is one of the most widely discussed problems in moral philosophy, often used to explore the tension between utilitarian and deontological ethics. SMBC frequently revisits the trolley problem, hence the "trolley-4" slug indicating this is one of several trolley-themed comics.