( Darwin ( ( coined ( ( the ( term fitness ) ) ( to ( ( refer ( to ( ( an ( organism 's ) ) ( relative ability ) ) ) ) ( to ( ( ( survive and ) produce ) ( fertile offspring ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Darwin)) (VP (VBN coined) (S (NP (DT the) (NN term) (NN fitness)) (VP (TO to) (VP (VB refer) (PP (TO to) (NP (NP (DT an) (NN organism) (POS 's)) (JJ relative) (NN ability))) (S (VP (TO to) (VP (VB survive) (CC and) (VB produce) (NP (ADJP (JJ fertile)) (NN offspring))))))))) (. .)))
Darwin coined the term fitness to refer to an organism's relative ability to survive and produce  fertile offspring.
(ROOT (S (NP (DT The) (NN term) (NN fitness)) (VP (VBZ describes) (NP (NP (DT the) (JJ overall) (NN ability)) (PP (IN of) (NP (DT an) (NN animal) (S (VP (TO to) (VP (VB survive) (CC and) (VB produce) (NP (NN offspring))))))))) (. .)))