Pope Innocent XI, born Benedetto Odescalchi, made considerable contributions to the Roman Catholic approach to embryology by condemning several propositions on liberal moral theology in 1679, including two related to abortion and ensoulment. His rejection of these principles strengthened the Church's stance against abortion and for the idea of "hominization," meaning the presence of human qualities before birth.

Mother Teresa, a Roman Catholic nun known for her charitable work and attention to the poor, was born 26 August 1910. The youngest child of Albanian parents Nikola and Drane Bojaxhiu, she was christened Agnes Gonxha Bojaxhiu and spent her early life in the place of her birth, present-day Skopje, in the Republic of Macedonia. In addition to her unwavering devotion to serve the sick and the poor, Mother Teresa firmly defended traditional Catholic teachings on more controversial issues, such as contraception and abortion. Indeed, her addresses to Western nations rarely excluded straightforward commentary on the social circumstances and disagreements taking place there. Mother Teresa, a renowned humanitarian, defended her religious beliefs regarding life issues and based her life on serving unwanted people in societies around the world until her death in 1997.

Pope John Paul II's views on abortion and embryology have been very influential to the Roman Catholic Church. He strictly forbade abortion and other threats to what he regarded as early human life in his encyclical entitled "Evangelium Vitae," meaning the "Gospel of Life." His authority on moral and social issues was highly regarded during his lifetime. Known around the world for his peace efforts and extensive writings on everything from poverty and Communism to contraception and reproductive issues, Pope John Paul II's legacy consists of his major contributions to the Roman Catholic Church' s body of doctrine and the effects of his long period of influence on Catholics and governments throughout the world.

Known for dropping a long-held distinction in the Catholic Church between the animated and unanimated fetus, Felice Peretti was born in Grottamare, Italy, in 1521, son of a Dalmatian gardener. In his early years, Peretti worked as a swineherd, but soon became involved in the local Minorite convent in Montalto, where he served as a novice at the age of twelve. He went on to study in Montalto, Ferrara, and Bologna, continuing his devotion to religious life, and in 1547 Peretti was ordained as priest in the city of Siena.

Quickening, the point at which a pregnant woman can first feel the movements of the growing embryo or fetus, has long been considered a pivotal moment in pregnancy. Over time, this experience has been used in a variety of contexts, ranging from representing the point of ensoulment to determining whether an abortion was legal to indicating the gender of the unborn baby; philosophy, theology, and law all address the idea of quickening in detail. Beginning with Aristotle, quickening divided the developmental stages of embryo and fetus. Indeed, this concept influenced the way embryology, human development, and hominization have been understood for over two thousand years.