 Aristotelians followed Aristotle and without much further study of embryos interpreted the process of generation, including human development, as gradual and epigenetic. Traditional Catholicism agreed. St. Augustine and St. Thomas Aquinas both held that hominization, or the coming into being of the human, occurs only gradually. Quickening was thought to occur around 40 days, and to be the point at which the merely animal mix of material fluids was ensouled. Until 1859, when Pope Pius IX decreed that life begins at “conception”, the Church was epigenetic along with the Aristotelians (see Maienschein 2003).