The only comprehensible explanation is that the vocation that had burrowed in next to medicine had taken control, had insisted.
( ( ( The ( only ( comprehensible explanation ) ) ) ( is ( that ( ( ( the vocation ) ( that ( had ( burrowed ( in ( next ( to medicine ) ) ) ) ) ) ) ( had ( taken control ) ) ) ) ) ) ( , ( ( had insisted ) . ) ) )
(ROOT (S (NP (NP (DT The) (RB only) (JJ comprehensible) (NN explanation)) (SBAR (S (VP (VBZ is) (SBAR (IN that) (S (NP (NP (DT the) (NN vocation)) (SBAR (WHNP (WDT that)) (S (VP (VBD had) (VP (VBN burrowed) (PP (IN in) (NP (NP (JJ next)) (PP (TO to) (NP (NN medicine)))))))))) (VP (VBD had) (VP (VBN taken) (NP (NN control)))))))))) (, ,) (VP (VBD had) (VP (VBN insisted))) (. .)))
The only explanation is that the job that had been close to medicine had wrestled control of it.
( ( The ( only explanation ) ) ( ( is ( that ( ( ( the job ) ( that ( had ( been ( close ( to medicine ) ) ) ) ) ) ( had ( wrestled ( control ( of it ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ only) (NN explanation)) (VP (VBZ is) (SBAR (IN that) (S (NP (NP (DT the) (NN job)) (SBAR (WHNP (WDT that)) (S (VP (VBD had) (VP (VBN been) (ADJP (JJ close) (PP (TO to) (NP (NN medicine))))))))) (VP (VBD had) (VP (VBN wrestled) (NP (NP (NN control)) (PP (IN of) (NP (PRP it))))))))) (. .)))