(S (S (BASENP (DT The) (NN study)) (VP (VP (VBD showed) (PRN (COMMA ,) (ADVP (RB however)) (COMMA ,))) (SBAR (IN that) (S (BASENP (DT the) (NN link)) (VP (VBD was) (VP (VBN found) (PP (ADVP (RB only)) (PP (IN in) (BASENP (JJ biological) (NNS brothers)))))))))) (PERIOD .))