The science of embryology says a new human being exists from fertilization

§ 1 The argument

Standard embryology holds that a new, living, genetically distinct human organism comes into being at fertilization. This is not a religious claim but the consensus of medical textbooks: the zygote is 'the beginning of a new human being,' and 'human development begins at fertilization.' Developmental milestones (implantation, heartbeat, pain, viability, birth) mark stages in the life of a human already in existence — they do not mark the arrival of a new kind of thing. Therefore the biological human being is present the whole time abortion is performed.

§ 2 Supporting points

• Moore & Persaud, The Developing Human: the zygote is the beginning of a new human being; development begins at fertilization.
• The offspring of two humans is, from the start, a whole human organism — not an organ of the mother and not another species.
• Milestones are changes of form and degree in one continuous organism, not changes of nature or kind.
• A distinct human genome and self-directed development are present from fertilization.

§ 3 Discussion questions

1. If a distinct human organism exists from fertilization, what morally relevant change happens at any later milestone that turns a non-person into a person?
2. Why do incremental bills draw lines at heartbeat or pain if the human being is present before those markers?

§ 4 Related

§ 5 References