( ( ( One ( common definition ) ) ( of ( a species ) ) ) ( ( is ( ( a group ) ( of ( organisms ( which ( ( ( ( can ( ( ( interbreed and ) produce ) ( fertile offspring ) ) ) , ) and ) ( ( can not ) ( mate ( with ( other species ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (CD One) (JJ common) (NN definition)) (PP (IN of) (NP (DT a) (NN species)))) (VP (VBZ is) (NP (NP (DT a) (NN group)) (PP (IN of) (NP (NP (NNS organisms)) (SBAR (WHNP (WDT which)) (S (VP (VP (MD can) (VP (VB interbreed) (CC and) (VB produce) (NP (ADJP (JJ fertile)) (NN offspring)))) (, ,) (CC and) (VP (MD can) (RB not) (VP (VB mate) (PP (IN with) (NP (JJ other) (NNS species)))))))))))) (. .)))
One common definition of a species is a group of organisms which can interbreed and produce fertile offspring, and cannot mate with other 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)) (. .)))