( ( That is ) ( , ( ( if ( ( two ( different animals ) ) ( have ( similar ( bone structures ) ) ) ) ) ( , ( then ( ( they ( must ( have ( evolved ( from ( the ( same ( original ancestors ) ) ) ) ) ) ) ) . ) ) ) ) ) )
(ROOT (S (INTJ (DT That) (VBZ is)) (, ,) (SBAR (IN if) (S (NP (CD two) (JJ different) (NNS animals)) (VP (VBP have) (NP (JJ similar) (NN bone) (NNS structures))))) (, ,) (ADVP (RB then)) (S (NP (PRP they)) (VP (MD must) (VP (VB have) (VP (VBN evolved) (PP (IN from) (NP (DT the) (JJ same) (JJ original) (NNS ancestors))))))) (. .)))
That is, if two different animals have similar bone structures, then they must have evolved from the same original ancestors.
(ROOT (S (NP (NP (DT The) (NN conclusion)) (SBAR (IN that) (S (NP (CD two) (NN animal) (NNS species)) (VP (VBD evolved) (PP (IN from) (NP (DT a) (JJ common) (NN ancestor))) (PP (IN in) (NP (JJ recent) (JJ geological) (NN history))))))) (VP (VBZ is) (ADVP (RBS best)) (VP (VBN supported) (PP (IN by) (NP (DT the) (NN observation))) (SBAR (IN that) (S (NP (DT the) (NNS species)) (VP (VBP have) (NP (JJ similar) (NN bone) (NN structure))))))) (. .)))
The conclusion that two animal species evolved from a common ancestor in recent geological history is best supported by the observation that the species have similar bone structure.