0001 AD: Here, eat this root.
1000 AD: That root is heathen. Here, say
this prayer.
1850 AD: That prayer is superstition.
Here, swallow this potion.
1940 AD: That potion is snake oil. Here,
swallow this pill.
1985 AD: That pill is ineffective. Here,
take this antibiotic.
2000 AD: That antibiotic is dangerous.
Here, eat this root.