The American Southwest is a fantastic place to study rock pocket mice with different fur coat colors. Ancestral pocket mice had light-colored fur coats that blended in with the rocks and sandy soil that was prevalent in the region. This kept the mice hidden from their predators (mainly owls).  Then, a series of volcanic eruptions spewed a river of black lava more than 40 miles long that wove right through the middle of pocket-mouse territory. Lava flows created huge patches of dark rock among the surrounding light-colored sand.

Today there are now two forms of pocket mice:

• light-colored mice that live on sandy soil
• dark-colored mice that live on black lava rock

Researchers noticed that rock pocket mice with a dark fur coat were more common on the dark lava flows, whereas the mice with light colored fur coat were more common on the light-colored sand. How might this have happened? 

In the next few lessons we will investigate this case of pocket mice evolution using computational models.

Let's start by watching a video developed by HHMI Biointeractive about this phenomenon.