I just spoke with Morty and Marty, the first cavemen. They assured me that they did not set fire to any forests; they loved the forests and all the little animals. They field-stripped their cigarettes and cigars, peed mightily on campfires.
"It was the Boy Scouts," said Morty. "They'd rub two sticks together, start a fire, toast marshmallows then go off chasing Girl Scouts. That's how forest fires began."