( ( What ( we ( fear ( most immediately ) ) ) ) ( ( is ( not ( extinction ( , ( but ( ( the ( insidious erosion ) ) ( of ( the ( human species ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (SBAR (WHNP (WP What)) (S (NP (PRP we)) (VP (VBP fear) (ADVP (RBS most) (RB immediately))))) (VP (VBZ is) (UCP (RB not) (ADVP (RB extinction)) (, ,) (CC but) (NP (NP (DT the) (ADJP (JJ insidious)) (NN erosion)) (PP (IN of) (NP (DT the) (JJ human) (NN species)))))) (. .)))
What we fear most immediately is not extinction, but the insidious erosion of the human species.
(ROOT (S (NP (NNP Human) (NNS actions)) (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (NP (NP (DT the) (NN extinction)) (PP (IN of) (NP (NP (NNS hundreds)) (PP (IN of) (NP (NP (NNS species)) (PP (IN of) (NP (NNS birds))))))))))) (. .)))