Why do people chew gum? If an anthropologist from Mars ever visited a typical supermarket, they'd be confounded by those shelves near the checkout aisle that display dozens of flavored gum options. Chewing without eating seems like such a ridiculous habit, the oral equivalent of running on a treadmill. And yet, people have been chewing gum for thousands of years, ever since the ancient Greeks began popping wads of mastic tree resin in their mouth to sweeten the breath. Socrates probably chewed gum.