Natural selection.

Step 1 of 6

Variation

In 19th-century England most peppered moths were pale, the colour of the lichen on tree bark. When coal-burning works blackened the trees with soot, a dark form, once very rare, became the majority in industrial areas within a few decades. The Scene is a model of that story.

Sort by shade is at Sorted by shade: each column is one wing shade, from pale to dark. The moths are not all the same shade. Those differences, the variation, are inherited: a moth passes its shade to its young, plus a small random change.

Step 2 of 6

Fifty generations

According to Charles Darwin, in $1859$⁠, three things are enough for a population to change: there is variation in a trait, the trait is inherited, and because of it some individuals survive and breed more than others. That is natural selection.

Here the bark is sooty, and the birds are hunting. Generation is fixed until you choose an answer.

Step 3 of 6

The catch

At the end of each generation the survivors breed a new generation of the same size. The birds in the Scene show, in a loop, the hunt of the current generation. Generation is fixed until you answer, and will then jump to generation $50$⁠.

Step 4 of 6

No birds

A population adapts to its surroundings when the traits that help survival there become common. But what exactly drives the change, the bark or the birds? Test it as in any experiment: change one thing only. Bird predation is fixed at $0\%$⁠: no birds at all.

Step 5 of 6

Matching the bark

Change Bark darkness, and see where the population settles.

Step 6 of 6

Populations, not individuals

Sort by shade is at Sorted by shade again, and the blue outlines show generation $0$⁠. All the columns have moved, but no moth changed colour: every moth in generation $50$⁠ was born with its shade.