If you take aspirin, you've got a pain reliever, heart attack preventer and possible cancer preventer rolled into one tablet. You might think that whoever invented aspirin is a genius, but the truth is humans have been using its natural equivalent for thousands of years. "Aspirin is one of those things that, long before there were ever clinical trials or any kind of scientific knowledge, people figured out, 'Hey, I feel better when I take this substance,' " said Dr. Karol Watson, assistant professor