Almost as a matter of principle, theological debates are insusceptible of empirical resolution. There’’s no scientific test to determine whether God is really three persons in one, for example, or whether salvation really comes through faith alone. Some Catholic thinkers, however, believe there is a growing body of empirical confirmation for at least one aspect of church teaching, which is Paul VI’’s 1968 assertion in Humanae Vitae on the immorality of separating the unitive and procreative functions of marriage. The toxic consequences of rewriting traditional concepts of marriage and the family, they believe, are grimly evident in the current demographic...