Robert George is an American legal scholar, political philosopher, and public intellectual who is the sixth McCormick Professor of Jurisprudence and director of the James Madison Program in American Ideals and Institutions at Princeton University. In 2013 in Conscience and Its Enemies: Confronting the Dogmas of Liberal Secularism, he argues on p. 166 when life begins,

The facts of human embryogenesis and early development make the conclusion inescapable: from a purely biological perspective, scientists can identify the point at which a human life begins. The relevant studies are legion. The biological facts are uncontested. The method of analysis applied to the data is universally accepted…Your life began, as did the life of every other human being, when the fusion of egg and sperm produced a new, complete, living organism—an embryonic human being. You were never an ovum or a sperm cell…But you were once an embryo, just as you were an adolescent, a child, an infant, and a fetus…You are the same being—the same human being—who once was an embryo.