It is not okay to call something a miracle without even trying to understand it. This is human developmental biology (human embryology, in terms of cells and molecules) for everyone curious enough to see it through, from the perspective of the business of becoming human - as individuals and as species; making new humans; how it happens (cells do it, ALL of it); and common variations of the process. It cannot be made quite simple and be kept quite true, but we will move as far toward simple as we can without losing touch with sound evidence. Variations from the ônormalö version of the process, particularly malformations and twinning and chimerism, figure prominently in the story because there is no better way to learn about the usual than to study the unusual and see what differences in the endings these observable differences at the beginnings can make. In this book, when technical terminology is the only way, or the best way, to say what needs to be said, it is defined and explained - making the words a worthwhile part of what is here to be learned. This book defines its own new field. We cannot claim to understand how anything [human] works [as human], with no effort at understanding the emergence of its form and functions. Old and new unanswered questions are waiting to be dug out from under old unquestioned answers about how becoming human unfolds.