But Daniel Callahan (who supports legal abortion), quoted in Francis Beckwith's "Defending Life," explains:
It is ... unscientific to call an embryo or fetus a mere "blueprint." Blueprints of buildings are not ordinarily mixed into the mortar; they remain in the hands of the architects. Moreover, once a building has been constructed, the blueprint can be thrown away, and the building will continue to stand. The genetic blueprint operates in an entirely different way: it exerts a directly causal action in morphological development; as an intrinsic part of the physiological structure, it can at no point be thrown away or taken out.The unborn isn't a blueprint for "building" a human organism; he or she is a human organism, fully programmed to develop himself or herself through the different stages of life. To say otherwise is a fundamental misunderstanding of the nature of living things.
In a section of Scott Klusendorf's new book "The Case for Life," he discusses the confusion about whether human embryos and fetuses are constructed (like buildings or cars) or whether they develop.
Embryos aren't constructed piece by piece from the outside; they develop themselves from within. That is to say, they do something no constructed thing could ever do: they direct their own internal growth and maturation, and this entails continuity of being. Unlike cars, developing embryos have no outside builder. They're all there just as soon as growth begins from within. In short, living organisms define and form themselves. An oak tree is the same entity that was once a shoot in the ground, years before it had branches and leaves.