The claim that we are uncertain about when life begins is often used to justify abortion, but uncertainty actually points in the opposite moral direction. When there is a real possibility that a human life is present, caution is required. Just as it would be criminally reckless to shoot into rustling bushes without knowing whether the movement is caused by a deer or a person, it is reckless to intentionally destroy what might be a human life. If human life could be present in the womb, killing should be avoided rather than permitted.
But the argument does not rest on uncertainty alone. It goes further and maintains that biology gives a clear answer: life begins at fertilization. At the moment sperm and egg fuse, a new, living organism comes into existence that is genetically distinct from both parents. This organism is human, with its own complete genetic blueprint. From that point forward, the same individual develops continuously through all later stages of life.
At fertilization, fundamental traits such as sex, ethnicity, and eye and hair color are already determined, and that genetic identity remains stable throughout development. Growth begins immediately and rapidly. Over time, this same human organism develops an early heartbeat, forms organs, shows measurable brain activity, makes coordinated movements, develops unique fingerprints, hears and recognizes the mother’s voice, and eventually becomes capable of surviving outside the womb at around 22 weeks or sometimes earlier. Labels such as zygote, embryo, and fetus simply name different stages in this continuous process and do not indicate a change in humanity.
Pregnancy, on this account, is not the creation of something nonhuman that later becomes human, but the nurturing of an already existing human being. The mother’s body undergoes changes in order to support and nourish this developing child. If life begins at fertilization and development is continuous from that point on, then abortion is not the removal of a non-living entity or a mere potential person, but the killing of an innocent human being.
Key Takeaways
If there is uncertainty about whether a human life is present, moral caution requires avoiding actions that could kill that life.
Biology identifies fertilization as the point at which a new, living, genetically distinct human organism comes into existence.
Human development is continuous from fertilization onward; terms like zygote, embryo, and fetus describe stages, not different kinds of beings.
Because abortion intentionally ends the life of this developing human, it constitutes the killing of an innocent human being.