The Silly Putty-like malleability of the institution [marriage], in fact, is the only reason we still have the thing at all. Very few people... would accept marriage on it's thirteenth-century terms. Marriage survives, in other words, precisely because it evolves. (Though I suppose this would not be a very persuasive argument to those who probably also don't believe in evolution).
Elizabeth Gilbert, Committed: A Skeptic Makes Peace with Marriage
marriage