Final answer:
Rock pocket mice have dark fur on black volcanic rock in New Mexico due to natural selection where the dark fur provides a selective advantage in camouflaging with the dark rocks to protect from predators.
Step-by-step explanation:
The best explanation for the phenomenon of rock pocket mice having dark fur on black volcanic rock in an area of New Mexico is natural selection. In this case, the dark fur color provides a selective advantage in blending in with the dark rocks, making the mice less visible to predators. Over time, through the process of natural selection, individuals with dark fur were more likely to survive and reproduce, passing on the dark fur trait to future generations.