Galápagos · Natural Selection
On a dry Galápagos island, finches live or die by their beaks. You control the weather — the finches do the evolving. Choose a season, run it, and watch natural selection reshape the flock.
Each finch is born with a beak depth measured in millimetres — a trait it inherits from its parents, with a little random variation. Small soft seeds can be eaten by almost any finch. Large, hard seeds can only be cracked by deep, strong beaks.
In wet years small seeds are everywhere, so beak size barely matters and the flock grows. In a drought, the soft seeds run out and only hard seeds remain — finches with deep beaks survive, the rest starve. The survivors pass their big beaks to the next generation, so the whole flock shifts.
This mirrors what Peter and Rosemary Grant measured on the real island of Daphne Major after the 1977 drought: average beak depth rose by about half a millimetre in a single generation. You are watching natural selection — the environment, not the bird's effort, decides which beaks win.