Richard Stith has made a distinction between construction of a car and development of a Polaroid photo that can help you understand and illustrate for friends how the unborn child is a human organism from the time of fertilization. You can read his entry-level treatment of this topic, “Arguing with Pro-Choicers” (First Things, Nov. 4, 2006), and his scholarly article, “Construction vs. Development: Polarizing Models of Human Gestation” (Kennedy Institute of Ethics Journal, 2014), through the link below.