Apopulation of deer mice with light-colored fur lives in sand hills, nebraska.
the ground in sand hills is light colored where glaciers have deposited sand
on top of dark soil. in contrast, areas outside sand hills have dark soil and
dark-furred mice. how did the mice in sand hills come to have light-colored
fur?

The constant presence of diseases or infectious agents within a given geographic area or population group. it may also refer to the usual prevalence of a given disease with such area or group. it includes holoendemic and hyperendemic diseases. a holoendemic disease is one for which a high prevalent level of infection begins early in life and affects most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do children (malaria in many communities is a holoendemic disease). a hyperendemic disease is one that is constantly present at a high incidence and/or prevalence rate and affects all groups equally. so probably family history.

The 4th of july  your welcome