(S (S (ADVP (RB However)) (COMMA ,) (S (NP (BASENP (DT the) (NNS samples)) (VP (VBN used) (PP (IN in) (BASENP (DT the) (NN analysis))))) (VP (VP (VBD came) (PP (IN from) (BASENP (DT the) (JJ past) (NN 120,000) (NNS years)))) (CC and) (VP (VBP show) (SBAR (IN that) (S (NP (BASENP (NN interbreeding)) (PP (IN of) (BASENP (DT the) (NN two) (NNS species)))) (VP (VBD occurred) (ADVP (BASENP (DT a) (JJ great) (NN deal)) (RBR earlier))))))))) (PERIOD .))