2000 AD: Here eat this root

1000 AD: Eating roots is pagan. Here say this prayer.

1850 AD: Prayer is superstition. Here drink think portion.

1940 AD: That portion is snake oil. Here swallow this antibiotic.

1985 AD: That antibiotic is ineffective. Here take this wonder drug.

2005 AD: That wonder drug is artificial. Here eat this root.

Laugh at this and then think about it!