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:
Our model spreads germs through mobile contacts
In this town model, walking dots meet other dots and pass a germ on. A dot in bed makes no new contacts. Real germs can also spread from people in bed, before symptoms, or by other routes.
"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. In this first model, slide it toward deadly to move dots into bed, where we give them no new contacts. Slide it toward mild and people keep walking and sharing it. Drive the dial and feel the lever.
4Now change when each germ can spread
Same meetings, different infectious times
Here is a new rule: feeling sick and being able to spread a germ do not have to start together. In two separate model groups, each starting person meets 5 new people in round 1, 3 in round 2, and 1 in round 3. All contacts while infectious transmit in this deliberately simple model; contacts never repeat.
Guess before you watch
Version A causes serious illness later, but can spread in rounds 1 and 2. Version B stays mild, but can spread only in rounds 2 and 3. Which starting person makes more new infections over these three rounds?