Inside the origins of modern Valentine's Day celebrations

The history of Valentine's Day is mushy.

It's been linked to a 12th-century poem about birds mating, the Christian-martyr-turned-Saint Valentine and a deadly fertility ritual in ancient Rome, but Elizabeth Nelson, an associate professor of history at the University of Nevada, Las Vegas, thinks that's all a stretch.

"We want there to be an origin," Nelson said. "We don't want this to be just a holiday invented by Hallmark."