( ( Natural selection ) ( ( ( occurs ( for ( ( a ( particular trait ) ) ( in ( ( one sex ) ( of ( an organism ) ) ) ) ) ) ) ( if ( it ( helps ( ( the organism ) ( ( survive and ) ( mate successfully ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Natural) (NN selection)) (VP (VBZ occurs) (PP (IN for) (NP (NP (DT a) (JJ particular) (NN trait)) (PP (IN in) (NP (NP (CD one) (NN sex)) (PP (IN of) (NP (DT an) (NN organism))))))) (SBAR (IN if) (S (NP (PRP it)) (VP (VBZ helps) (S (NP (DT the) (NN organism)) (VP (VP (VB survive)) (CC and) (VP (VB mate) (ADVP (RB successfully))))))))) (. .)))
Natural selection occurs for a particular trait in one sex of an organism if it helps the organism survive and mate successfully.
(ROOT (S (NP (JJ Natural) (NN selection)) (VP (VBZ is) (NP (NP (DT the) (NN process)) (SBAR (WHNP (WDT that)) (S (VP (VBZ allows) (NP (NNS organisms)) (PP (IN with) (NP (JJR better) (NNS traits) (S (VP (TO to) (VP (VB survive) (CC and) (VB produce))))))))))) (. .)))