A new book, Catching Fire: How Cooking Made Us Human, argues that hot food, and not sex, is the reason human beings originally paired up in domestic relationships.
According to author and Harvard anthropologist Richard Wrangham, early marriages were really a trade off for hot food (prepared by the women) and protection (provided by the men). Evidence from primitive societies, including the fact that society tolerated women sleeping around but ostracized them if they ever cooked for men besides their husbands, is used to support the conclusion.
It seems that a domestic convention that is considered backward today actually made us move forward evolutionarily. Let's hope modern men won't use this finding as a reason to expect women to do all the cooking!