The beginning of human embryonic development Human embryonic development begins with the process of egg fertilization, that is, the combination of sperm and egg to form a fertilized egg. In the female body, the place where the egg and sperm combine is the fallopian tube. After about 6-7 days of division and development, the fertilized egg finally enters the uterine cavity. At this point, the embryo begins to differentiate into different cell layers. The initial cells differentiate to form the ectoderm, endoderm, and inner and outer layers of the protogut. This process is human