( ( ( ( Any time ) ( two groups ) ) ( are ( so ( different ( that ( they ( ( can not ) ( reproduce ( to ( produce ( ( healthy fertile ) offspring ) ) ) ) ) ) ) ) ) ) ) ( , ( ( both concepts ) ( ( consider ( them ( to ( be ( separate species ) ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (NP (DT Any) (NN time)) (NP (CD two) (NNS groups))) (VP (VBP are) (ADJP (RB so) (JJ different) (SBAR (IN that) (S (NP (PRP they)) (VP (MD can) (RB not) (VP (VB reproduce) (S (VP (TO to) (VP (VB produce) (NP (ADJP (JJ healthy) (JJ fertile)) (NN offspring)))))))))))) (, ,) (NP (DT both) (NNS concepts)) (VP (VBP consider) (S (NP (PRP them)) (VP (TO to) (VP (VB be) (NP (JJ separate) (NNS species)))))) (. .)))
Any time two groups are so different that they can not reproduce to produce healthy fertile offspring, both concepts consider them to be separate species.
(ROOT (S (SBAR (IN If) (S (NP (CD two) (NNS populations)) (VP (VBP do) (RB not) (VP (VB mate) (CC and) (VB produce) (NP (ADJP (JJ fertile)) (NN offspring)))))) (, ,) (NP (JJ separate) (NNS species)) (VP (VBP result)) (. .)))