What discovery led to George B. McClellan's victory over Robert E. Lee at Antletam?
General McClellan found the Confederate troop roster.
Union troops studied Confederate fighting tactics.
General McClellan found General Lee's battle plan,
President Lincoln uncovered the South's European alliance.

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.

Charles darwin