If the face has been getting longer at the bottom over the generations, it has been getting shorter (and broader) on top.
( ( If ( ( the face ) ( has ( been ( ( getting ( longer ( at ( the bottom ) ) ) ) ( over ( the generations ) ) ) ) ) ) ) ( , ( it ( ( has ( been ( getting ( ( shorter ( -LRB- ( and ( broader -RRB- ) ) ) ) ( on top ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (DT the) (NN face)) (VP (VBZ has) (VP (VBN been) (VP (VBG getting) (ADVP (RB longer) (PP (IN at) (NP (DT the) (NN bottom)))) (PP (IN over) (NP (DT the) (NNS generations)))))))) (, ,) (NP (PRP it)) (VP (VBZ has) (VP (VBN been) (VP (VBG getting) (NP (NP (JJR shorter) (PRN (-LRB- -LRB-) (CC and) (ADJP (JJR broader)) (-RRB- -RRB-))) (PP (IN on) (NP (NN top))))))) (. .)))
The face gets longer and thinner at the bottom throughout the generations.
( ( The face ) ( ( gets ( ( ( longer and ) thinner ) ( at ( ( the bottom ) ( throughout ( the generations ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN face)) (VP (VBZ gets) (NP (NP (JJR longer) (CC and) (JJR thinner)) (PP (IN at) (NP (NP (DT the) (NN bottom)) (PP (IN throughout) (NP (DT the) (NNS generations))))))) (. .)))