1What a germ needs to get around
A germ rides on people — and "winning" means reaching the most of them
You only need two ideas. Watch each one:
A germ only spreads through a person who's out and about
Germs jump from one person to the next when they're close. A person walking around — school, the bus, a party — bumps into lots of people. A person stuck in bed bumps into almost no one, so the germ inside them goes nowhere.
"Winning" just means ending up in the most people
A germ doesn't care about being scary. The version that copies itself into the most new people becomes the common one. That — and only that — is what "winning" means for a germ.
2Two kinds of germ
The knock-you-flat germ vs the keep-you-walking germ
Imagine the same town catches two different germs. They make people sick in opposite ways:
The knock-you-flat germ
Hits hard and fast — its host feels awful and stays in bed, where they meet almost nobody.
The keep-you-walking germ
Barely a sniffle — its host feels fine enough to keep wandering around, bumping into people.
3Your turn — be the germ's dial
Push one germ from mild to deadly and watch the town
Here's one germ loose in a town. Slide it toward deadly and it floors people into bed — but a person in bed meets no one, so it has trouble spreading. Slide it toward mild and people keep walking and sharing it. Drive the dial and feel the lever.
4Now race them — both germs, one town
Release both germs at once. Which one takes over?
Forget the dial. This time we drop the deadly-and-slow germ AND the mild-and-fast germ into the very same town at the same moment, and let them fight for every person. Guess the winner first — then watch the race.
Guess before you watch
Two germ versions in one town: one super deadly but slow, one mild but spreads fast. After a few months, which one has taken over and become the common version?