This new organism, the embryo, now residing in the ampulla of her mother’s fallopian tube, is distinct from any cell or part of the mother and from any cell or part of the father. For (much like the six-week-old infant) she acts independently, developing herself in accord with her own distinct genetic and epigenetic program, growing in her own direction, toward her own survival and maturation. The embryo’s development is very rapid in the first several weeks. For example, as early as eight or ten weeks of gestation, she (now called a fetus) has a fully formed beating heart, a complete brain (though not all of its synaptic connections are complete, nor will they be until sometime after the child is born) and a recognizably human form. She cries, and even sucks her thumb.

Second, this singular organism is obviously human: She has the genetic makeup characteristic of humans, is a product of humans, and develops along a human trajectory.

And third — and perhaps the most important point so far — the human embryo is a whole human being, not functionally a part, such as human tissues or human cells are. For, by a continuous process of internally directed growth, this new being actively develops herself toward the mature stage of a human being. There is no stage after fertilization at which there occurs a fundamental change in the developmental trajectory. What this shows is that at fertilization a whole, albeit immature, human organism comes to be. This new human being, provided she has a suitable environment and nutrition, will actively develop herself through the fetal stage and then through the infant stage, the toddler stage, and on to adulthood, the same being at every stage.