Answer:
Black fur is more fit to survive in the environment than other colors of fur.
Explanation:
"Fitness", in terms of natural selection, is an organism's likelihood to survive in a given environment. Assuming that the increase in black fur is significant (Not attributable to pure chance), we can safely assume this is because Black Fur provides a competitive advantage in said environment over other colors of fur. There may be black terrain that allows them to blend into the environment and ovoid predators, or maybe it keeps them warmer if it is located in a cold region, thereby reducing the amount of resources they need to spend to stay warm.
A branch or leaf and here is a link to some flash cards i found
https://quizlet.com/45759526/developmental-anatomy-flash-cards/
Write in your own words:
"Since the mouse is an endotherm, it probably has a higher metabolic rate, and thus a faster growth rate, than the lizard (an ectotherm of similar size) does. If the mouse has a faster growth rate, its bones would grow more between each ring, resulting in wider bone rings."
: )
and remember that a mouse is a endotherm because it generates metabolic heat to maintain internal body temperature.