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.