A father is traditionally the male parent of a child. Like mothers, fathers may be categorised according to their biological, social or legal relationship with the child. Historically, the biological relationship paternity has been determinative of fatherhood. However, proof of paternity has been intrinsically problematic and so social rules often determined who would be regarded as a father e.g. the husband of the mother. This method of the determination of fatherhood has persisted since Roman times. The historical approach has been destabilised with the recent emergence of accurate scientific testing, particularly DNA testing. As a result, the law on fatherhood is undergoing rapid changes. In the United States, the Uniform Parentage Act essentially defines a father as a man who conceives a child through sexual intercourse.