NOTES
Two models of how embryos develop seemed to be the only possible choices - preformation which postulates that the embryo develops from parts already present (a conceit used in Ted Chiang's brilliant "Seventy-Two Letters", and epigenesis, in which the embryo develops from undifferentiated material. But both possibilities had fatal flaws - the problem of infinite regression for preformation, and the problem of how the undifferentiated material “knows” how to shape itself - on one hand scientists were faced with the silly idea of hundreds of embryos imbedded one within the next, and the unappealing idea of some mystical field telling the embryo how to develop. The solution was a model from another field - that of computer science: Von Neumann's model of reproduction involving a constructor and a blueprint.