It is an obvious yet remarkable fact that a fetus, near the end of pregnancy, could as easily be a newborn baby. Whether through natural birth or c-section, removing the full term fetus from the mother is all that is necessary to transform it into a baby. One remarkable thing about this is that a baby is an air-breathing animal much like any other, and a fetus does all its gas exchange through a tube attached to its circulatory system through its belly button. I can’t easily imagine keeping a tortoise alive by sticking a tube into its belly, nor do I imagine one would have much luck doing so with an adult human, or even a child. But somehow it works for the fetus.
Another thing that is striking about the fetus being a nearly complete baby is that it is a nearly complete baby entirely inside the belly of the mother, upside-down, often with its head inside her pelvis. I don’t know about you, but I could not function for very long with a nearly full sized baby inside me and a skull in the middle of my pelvis. I think I wouldn’t last five minutes, but apparently this situation can go for weeks with little danger, and bearable discomfort, to possessor of either pelvis or skull.
A tremendous amount is now known about ontogenesis, the process by which a single egg grows and develops into a whole person. We have studied it on the scale of molecules, cells, tissues, organs and whole individuals and from the perspectives of physiology, genetics and evolution. There are still vast areas we know almost nothing about, but we can largely reject the hypothesis that there is magic involved. Never the less, things can feel like magic even when reason rejects it. This whole process, of self-directed growth of a single cell into a person, makes it easy to understand why spirits, gods and humunculi are so often invoked.