A unit of one or more populations of individuals that can reproduce under normal conditions, produce fertile offspring, and are reproductively isolated from other such units.<ref>Wile, Dr. Jay L. ''Exploring Creation With Biology''. Apologia | A unit of one or more populations of individuals that can reproduce under normal conditions, produce fertile offspring, and are reproductively isolated from other such units.<ref>Wile, Dr. Jay L. ''Exploring Creation With Biology''. Apologia |