Christian missionaries, who typically spend large parts of their lives in remote, often dangerous places, have had disproportionate impact compared with their numbers worldwide for centuries. Communist revolutionaries in the 20th century had similar dedication and outsized impacts. International relief organizations such as Doctors Without Borders, Save the Children and Amnesty International have benefited millions, while also occasionally costing workers their lives. For better and for worse, humans can conceive of, and sacrifice for, an almost infinite variety of causes in addition to their biological kin.