The ArgumentBlood tests developed at the turn of the century could in some cases discern genetic relations. While such tests could never prove that a given individual had fathered a child in question, men of certain blood types could be exonerated from paternity of children with other blood types. Starting in the 1930s, scientists and lawmakers attempted to introduce such evidence into paternity or bastardy trials to attest to a man's innocence. Evidence from blood tests soon came to be used (...) in divorce cases.Blood tests appeared to be ideal for providing relevant information in cases when divorcing men claimed as a part of their suit that they had not fathered their ex-wife's child or children. Nevertheless, the courts remained reluctant to intro duce such evidence in divorce cases. This paper will argue that reluctance derived not from a distrust of the science, but from the courts' clinging to a definition of paternity that was not rooted in genetic connection.Many judges and juries fell back on the pre-industrial assumption that once a man married a woman he was automatically the father of any children she bore. While this assumption flew in the face of scientific evidence, it did have the advantage of ensuring that the children of married women could not be bastard ized. The changing manner in which courts handled the tension between genetic paternity and traditional paternity in divorce cases reveals how society's views on paternity have evolved over the course of this century. (shrink)