The life of a new organism of the human species starts at the moment of fertilization. This is when the sperm and oocyte plasma membranes fuse. The ovarian continuum begins at fertilization, when the zygote starts its development.

Until now, a biological dogma has been that all sex differences in the brain arise from differences in the gonadal secretions. It has recently been demonstrated that the whole genome of males and females seems to be different; not only are the sexual chromosomes different, but also autosomes have a major role in sexual differentiation. For our purposes this will be very important to keep in mind, because during this lecture I would like to invite you to look at ourselves the way we were created. I would also like to invite you to look at the many instances by which this creation can be distorted.

Approximately 2 months after fertilization occurs, the future oogonia, called primordial germ cells at this time, leave the embryo and migrate to the vitelline sac in order to escape the process of cell differentiation. Some four weeks later these cells migrate to the region of the future ovary, the gonadal crest, and start
their process of differentiation, forming millions of primordial follicles. At this time some 7 million primordial follicles are formed, most of which will undergo atresia. When the girl is born, 1 to 2 million follicles containing the oocytes remain. Of these, about 475 will complete folliculogenesis during ovulation.