When does disruptive selection occur?

Disruptive selection occurs when extreme phenotypes are favored over intermediate ones. This can happen when the environment changes rapidly, and the population needs to adapt quickly.

For example, imagine a population of rabbits. The rabbits are living in a forest, and their fur is brown. This fur color helps them camouflage themselves from predators.

Suddenly, the environment changes. The forest is cleared, and the rabbits are now living in a field. The brown fur is no longer as effective at camouflaging the rabbits, and they are starting to get picked off by predators.

The rabbits that have fur that is either very light or very dark are the ones that are most successful at camouflaging themselves. The light-furred rabbits are able to blend in with the grass, and the dark-furred rabbits are able to blend in with the trees. The intermediate-furred rabbits are the most visible to predators, and they are the ones that are most likely to get picked off.

Over time, the frequency of the light- and dark-furred rabbits increases in the population, and the frequency of the intermediate-furred rabbits decreases. This is an example of disruptive selection.