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When did I begin? When does any individual human being begin? At what stage of its development does a human organism become entitled to the moral status and legal protection that we give to the life of a human adult? Is it at conception, at birth, or somewhere between the two?

The three alternatives–at conception, at birth, or between–do not in fact exhaust the possibilities. Plato, and some Jewish and Christian admirers of Plato, thought that individual human persons existed as souls before the conception of the bodies they would eventually inhabit. This idea found expression in the Book of Wisdom, where Solomon says, “I was a boy of happy disposition: I had received a good soul as my lot, or rather, being good, I had entered an undefiled body.” Clement of Alexandria records an early Christian notion that the soul was introduced by an angel into a suitably purified womb.

In addition to those who thought that the individual soul existed before conception, there have been those who thought that the individual body existed before conception, in the shape of the father’s semen. Onan, in Genesis, spilled his seed on the ground; Jewish tradition saw this act not only as a form of sexual pollution but as an offense against life. Thomas Aquinas, in a chapter on “the disordered emission of semen” in the Summa contra Gentiles, treats both masturbation and contraception as a crime against humanity, second only to homicide. Such a view is natural in the context of a biological belief that only the male gamete provides the active element in conception, so that the sperm is an early stage of the very same individual as eventually comes to birth. Masturbation is then the same kind of thing, on a minor scale, as the exposure of an infant. The high point of this line of thinking was the bull Effraenatam of Pope Sixtus V (1588), which imposed an excommunication, revocable only by the Pope himself, on all forms of contraception as well as on abortion. But the view that masturbation is a poor man’s homicide cannot survive the knowledge that both male and female gametes contribute equally to the genetic constitution of the offspring.

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