( ( New ( Species May ) ) ( ( Form ( When ( ( Members ( of ( Once ( Isolated Populations ) ) ) ) ( Interbreed ( upon Contact ) ) ) ) ) . ) )
(ROOT (S (NP (NNP New) (NNPS Species) (NNP May)) (VP (VBZ Form) (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS Members)) (PP (IN of) (NP (NNP Once) (NNP Isolated) (NNP Populations)))) (VP (VBD Interbreed) (PP (IN upon) (NP (NNP Contact))))))) (. .)))
New Species May Form When Members of Once Isolated Populations Interbreed upon Contact.
(ROOT (S (NP (NP (DT All) (NNS members)) (PP (IN of) (NP (DT a) (NN species) (NN living)))) (ADVP (RB together)) (VP (VB form) (NP (DT a) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN population))) (. .)))