Various debates have focused on questions about the personhood of different classes of entities. Historically, the personhood of women, and slaves has been a catalyst of social upheaval. In most societies today, postnatal humans are defined as persons. Likewise, certain legal entities such as corporations, sovereign states and other polities, or estates in probate are legally defined as persons. However, some people believe that other groups should be included, depending on the theory, the category of "person" may be taken to include or not pre-natal humans or such non-human entities as animals, artificial intelligences, or extraterrestrial life.