Some foods are so weird that we have to wonder who first tried eating them. Chewing gum is one of them. Gum is naturally made in trees: it's the "resin" or sap that oozes up and down the inside of the trunk. About 9,000 years ago humans started chewing the gum from birch trees. Remember, it didn't taste like mint or pink bubble gum -- it probably tasted more like dirt. Today we make 374 TRILLION sticks of gum every year, because it tastes a lot better now!