( ( The ( first ( thing ( to ( realize ( about ( the brain ) ) ) ) ) ) ) ( ( is ( that ( , ( ( unlike ( ( an organ ) ( such ( as ( ( ( the heart ) or ) liver ) ) ) ) ) ( , ( it ( ( is not ) ( ( a ( single organ ) ) ( with ( a ( single function ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ first) (NN thing) (S (VP (TO to) (VP (VB realize) (PP (IN about) (NP (DT the) (NN brain))))))) (VP (VBZ is) (SBAR (IN that) (S (, ,) (PP (IN unlike) (NP (NP (DT an) (NN organ)) (PP (JJ such) (IN as) (NP (NP (DT the) (NN heart)) (CC or) (NP (NN liver)))))) (, ,) (NP (PRP it)) (VP (VBZ is) (RB not) (NP (NP (DT a) (JJ single) (NN organ)) (PP (IN with) (NP (DT a) (JJ single) (NN function)))))))) (. .)))
The first thing to realize about the brain is that, unlike an organ such as the heart or liver, it is not a single organ with a single function.
(ROOT (S (PP (IN In) (NP (NNS humans))) (, ,) (NP (DT the) (NN heart)) (VP (VBZ is) (NP (DT the) (JJ first) (NN organ) (S (VP (TO to) (VP (VP (VB form)) (CC and) (VP (VB become) (ADJP (JJ functional)))))))) (. .)))