How to use this natural selection simulation
Here the Natural selection lab starts on meadow a1: about 110 rabbits bred slow (around 82% of normal speed) and short-sighted (around 85% sight), and 8 foxes. Press Start, keep Graphs on Traits, and run it at 8× or 16×. Each line is one inherited trait, averaged over every living rabbit. Tap a rabbit to follow it: its card lists its own speed, size and sight and which generation it belongs to.
Why the averages move
Three things are happening at once, which are the three ingredients of natural selection:
- Variation. No two rabbits are the same: each kit’s traits are its parents’ average plus a small random change.
- Inheritance. Those traits pass from parents to young.
- Different survival. A fox’s pounce is a short burst; a quicker rabbit jinks away more often and outruns the fox once the burst is spent. It lives longer and has more litters, so its speed becomes more common.
In our test run of this meadow (September 2026), average rabbit speed climbed from 82% to 89% in four years, about a point every half year, with 14 to 110 foxes on the meadow at those half-yearly counts. Sight crept up too, from 85% to 93%, most of it in the last two years, while size stayed between 95% and 97%. On five other test meadows speed also ended higher than it started, by 4 to 10 points after four years. Chance matters: your run will differ.
Where the idea comes from
Charles Darwin and Alfred Russel Wallace presented natural selection in a joint paper to the Linnean Society of London in 1858, and Darwin set it out in full in On the Origin of Species in 1859. A classic case of predators doing the selecting is the peppered moth: as soot darkened tree trunks in industrial England, dark moths hid better from birds and became nearly all of the moths around Manchester; when cleaner air returned after the Clean Air Act of 1956, the pale form came back.
Things to try
- Take the foxes away after a year or two and see whether speed holds or slips back.
- Bring harsh winters one after another and watch whether the size line answers.
- Switch the chart to Foxes: they are being selected as well, for catching rabbits.