Humanities · Game Theory

Tragedy of the Commons

A shared pasture. Five farmers. Each wants to add more livestock — but the grass is finite. When everyone maximises their own herd, the common resource collapses. Can you find the strategy that sustains the commons?

The Dilemma

  • Individual payoff — each extra animal earns money for the farmer
  • Shared cost — overgrazing degrades the pasture for everyone
  • Nash Equilibrium — the "rational" choice leads to collective ruin
  • Solutions: quotas, taxes, privatisation, or voluntary cooperation

The Shared Pasture

Pasture Health

100%

Your Decision — Each Round, Choose How Many to Graze

You (Farmer 1)

3
Herd size: 3

Farmer 2 (AI)

3
Strategy: Greedy

Farmer 3 (AI)

3
Strategy: Cooperative

Farmer 4 (AI)

3
Strategy: Tit-for-Tat

Farmer 5 (AI)

3
Strategy: Random

Resource & Wealth Over Time

Green = pasture health · Colored lines = each farmer's cumulative wealth

Garrett Hardin (1968)

Published "The Tragedy of the Commons" — arguing that shared resources are inevitably overexploited without regulation.

Nash Equilibrium

Each farmer's "best response" is to add livestock — even knowing the system will collapse. No individual can improve their outcome by changing alone.

Elinor Ostrom

Won the 2009 Nobel Prize by proving communities can self-govern commons successfully — without privatization or top-down regulation.

Modern Commons

Climate change, ocean fisheries, and internet bandwidth are today's "commons." The same game theory applies at planetary scale.