2000 B.C. - Here, eat this root
1000 A.D. - That root is heathen. Here, say this prayer.
1850 A.D. - That prayer is superstition. Here, drink this potion.
1940 A.D. - That potion is snake oil. Here, swallow this pill.
1985 A.D. - That pill is ineffective. Here, take this antibiotic.
2000 A.D. - That antibiotic doesn't work anymore. Here, eat this root.