( ( According ( to ( this definition ) ) ) ( , ( ( one species ) ( ( ( is ( distinguished ( from another ) ) ) ( when ( , ( ( in nature ) ( , ( it ( ( is not ) ( possible ( for ( matings ( between ( individuals ( from ( each ( species ( to ( produce ( fertile offspring ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (VBG According) (PP (TO to) (NP (DT this) (NN definition)))) (, ,) (NP (CD one) (NNS species)) (VP (VBZ is) (ADJP (JJ distinguished) (PP (IN from) (NP (DT another)))) (SBAR (WHADVP (WRB when)) (S (, ,) (PP (IN in) (NP (NN nature))) (, ,) (NP (PRP it)) (VP (VBZ is) (RB not) (ADJP (JJ possible) (PP (IN for) (NP (NP (NNS matings)) (PP (IN between) (NP (NP (NNS individuals)) (PP (IN from) (NP (DT each) (NN species) (S (VP (TO to) (VP (VB produce) (NP (ADJP (JJ fertile)) (NN offspring)))))))))))))))) (. .)))
According to this definition, one species is distinguished from another when, in nature, it is not possible for matings between individuals from each species to produce fertile offspring.
(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)) (. .)))