D'Emilio and Freedman, who are historians of sexuality, note that historical use of the missionary position in the US is marked by social class as well as ethnicity. In the 19th century, white settlers and Protestant missionaries who moved West attempted to assimilate Native American, Mexican, and immigrant peoples into the sexual values held by the middle classes in the American north. These authors also note that the Kinsey studies revealed social class influences, with working class men preferring to use the missionary position over other sexual positions.