What's Happening?

On this tiny island in the middle of the ocean, the wind has brought two tiny seeds to rest.

Soon, they start to grow. The bright sunshine gives them energy, and they grow tall. Finally, they mature, and start to make their own seeds, which are blown by the wind around the island, until they too land and start to grow.

Each new plant inherits its genes from its parent. There is one tiny difference in those genes - one gives the plant a reddish stem, the other a pale stem. And one of them is a tiny bit better (0.5%) at converting sunlight into energy.

The island is not so big. Some plants unluckily start to grow in the shade of a larger one. These plants don't look so healthy. They don't grow so tall, nor make as many seeds.