March Madness begins today. And that means everyone is scrambling to finish their brackets. Well, almost. An estimated 45 percent of Americans fill out the brackets with their predictions of the results each year, and Barack Obama has referred to the practice as “a national pastime.”

But what about the history of the bracket? Where does its origin lie? According to this piece in The Wall Street Journal, the bracket isn’t a modern invention and may have originated with the Greeks:

Steven Murray, a Colorado Mesa University professor who has studied the history of sports, said the concept that inspired the bracket—a single-elimination sporting competition with many rounds—isn’t a modern invention. He said the ancient Greeks held wrestling and boxing competitions starting around 700 B.C. where the combatants would draw lots to set pairings.

If the tournament pairings were posted in a bracket form, Murray said, they probably would have been painted with pigment on scrolls, placards or walls and wouldn’t have survived.

But perhaps the modern bracket had its origins with a more familiar concept, the family tree:

Several historians, when confronted with the question, speculated that the basketball bracket could have its roots in another organizational art form: the family tree. Brenton Simons, president and chief executive of the New England Historic Genealogical Society, said renderings of family trees date at least to the 18th century in the U.S. and stretch back centuries before in other countries.

Most likely, the modern rendition of the sports bracket can be traced to England with the Lawn Tennis Championship at Wimbledon.

So basically, the origin of the bracket is still a mystery. Click here to view a slideshow accompanying the article showcasing various brackets throughout history. For more info on the history of the bracket, see this explainer in Slate.