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 is artificial. Here, eat this root.