You want to know if black squirrels or brown squirrels have a greater birth rate. Your ALTERNATIVE hypothesis is:.

Natural selection is a mechanism of evolution proposed by Charles Darwin. It is the differential survival and reproduction of individual due to the difference in the phenotype. Over time, this process results in populations which are better adapted to their environment as they tend to survive and produce new offspring.  The brown squirrels with thick coat survive at a higher rate than the brown sqirrels without the thick coat. Thick coat is a adaptation for survival in cold winters which are chosen over the other and allowed to reproduce.

Explanation:

not sure if this is what you'r looking for nnew= nold