( ( ( ( ( ( 2 -RRB- ) ( Mammoths ( ( became ( extinct ( on ( the Plains ) ) ) ) ( by ( ( 11,000 years ) ago ) ) ) ) ) , ) and ) ( ( although ( ( paleo-ecological conditions ) ( were worsening ) ) ) ( , ( ( ( the demise ) ( of mammoths ) ) ( may ( have ( been ( hastened ( by ( human predation ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (LST (LS 2) (-RRB- -RRB-)) (NP (NNP Mammoths)) (VP (VBD became) (ADJP (JJ extinct) (PP (IN on) (NP (DT the) (NNPS Plains)))) (PP (IN by) (ADVP (NP (CD 11,000) (NNS years)) (RB ago))))) (, ,) (CC and) (S (SBAR (IN although) (S (NP (JJ paleo-ecological) (NNS conditions)) (VP (VBD were) (NP (VBG worsening))))) (, ,) (NP (NP (DT the) (NN demise)) (PP (IN of) (NP (NNS mammoths)))) (VP (MD may) (VP (VB have) (VP (VBN been) (VP (VBN hastened) (PP (IN by) (NP (JJ human) (NN predation)))))))) (. .)))
2) Mammoths became extinct on the Plains by 11,000 years ago, and although paleo-ecological conditions were worsening, the demise of mammoths may have been hastened by human predation.
(ROOT (S (NP (JJ Woolly) (NNS mammoths)) (VP (VBD began) (S (VP (TO to) (VP (VB go) (NP (NP (ADJP (JJ extinct)) (NNS thousands)) (PP (IN of) (NP (NNS years)))) (ADVP (RB ago) (PP (IN because) (PP (IN of) (S (VP (VBG hunting) (PP (IN by) (NP (NNS humans)))))))))))) (. .)))
Woolly mammoths began to go extinct thousands of years ago because of hunting by humans.