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.