In 1955, Frank Sinatra recorded the song "Love and Marriage," in which he informed us that the two titular subjects go together like a horse and carriage. By Frank's era, that was true -- humans were on the search for soul mates that would serve as lovers, co-parents and best friends. But for most of human history, marriage wasn’t a very romantic institution. It was more akin to a business deal between men, and the bride in question had very few rights or other options. Love has never been out of the question for our ancestors; they just didn't always believe that such a thing could be found within marital bonds. So how did marriage become associated with love? Let's trace the development of this institution.