( Actually ( ( fitness ( in ( the ( biological sense ) ) ) ) ( ( ( refers only ) ( to ( the ( capacity ( to ( produce ( ( surviving offspring ) ( who ( ( in turn ) ( live ( to reproduce ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (ADVP (RB Actually)) (NP (NP (NN fitness)) (PP (IN in) (NP (DT the) (JJ biological) (NN sense)))) (VP (VBZ refers) (ADVP (RB only)) (PP (TO to) (NP (DT the) (NN capacity) (S (VP (TO to) (VP (VB produce) (NP (NP (VBG surviving) (NN offspring)) (SBAR (WHNP (WP who)) (S (PP (IN in) (NP (NN turn))) (VP (VBP live) (S (VP (TO to) (VP (VB reproduce)))))))))))))) (. .)))
Actually fitness in the biological sense refers only to the capacity to produce surviving offspring who in turn live to reproduce.
(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))))))))) (. .)))