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>Freeman, Scott. ''Biological Science''. Prentice Hall 2005</ref>
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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