I have an earache. 2000 B.C. - Here, eat this root. 1000 A.D. - That root is heathen, say this prayer. 1850 A.D. - That prayer is superstition, drink this potion. 1940 A.D. - That potion is snake oil, swallow this pill. 1985 A.D. - That pill is ineffective, take this antibiotic. 2003 A.D. - That antibiotic is artificial. Here, eat this root.