As a metter of fact, it begins before then. Every female born already has all the eggs in her she will ever have. While she is in the womb. So every person alive spent some time (at least their protoplasm) in their maternal grandmother's body, whether they ever even met her or not.
The flowing continuum of the life cycle, complete with tributaries. Yet many folks oddly believe there is a magical "poof" at which a human being suddenly pops into existence.
A few months ago, a paper was published that shows that mammalian females, including humans, have stem cells in the ovaries and continue to make new oocytes our entire fertile life.
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v428/n6979/full/428133b_fs.html
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v428/n6979/abs/nature02316_fs.html&dynoptions=doi1089066123Germline stem cells and follicular renewal in the postnatal mammalian ovary.
""Germline stem cells and follicular renewal in the postnatal mammalian ovary.
Johnson J, Canning J, Kaneko T, Pru JK, Tilly JL.
Vincent Center for Reproductive Biology, Vincent Obstetrics and Gynecology Service, Massachusetts General Hospital, and Department of Obstetrics, Gynecology and Reproductive Biology, Harvard Medical School, Boston, Massachusetts 02114, USA.
A basic doctrine of reproductive biology is that most mammalian females lose the capacity for germ-cell renewal during fetal life, such that a fixed reserve of germ cells (oocytes) enclosed within follicles is endowed at birth. Here we show that juvenile and adult mouse ovaries possess mitotically active germ cells that, based on rates of oocyte degeneration (atresia) and clearance, are needed to continuously replenish the follicle pool. Consistent with this, treatment of prepubertal female mice with the mitotic germ-cell toxicant busulphan eliminates the primordial follicle reserve by early adulthood without inducing atresia. Furthermore, we demonstrate cells expressing the meiotic entry marker synaptonemal complex protein 3 in juvenile and adult mouse ovaries. Wild-type ovaries grafted into transgenic female mice with ubiquitous expression of green fluorescent protein (GFP) become infiltrated with GFP-positive germ cells that form follicles. Collectively, these data establish the existence of proliferative germ cells that sustain oocyte and follicle production in the postnatal mammalian ovary.
PMID: 15014492 [PubMed - indexed for MEDLINE]""
Science continues to add to our knowledge, and occasionally, new discoveries completely debunk old "Knowledge." And because this is true(at least as far as we know), it's vital that science and scientists be held to the ancient "First, do no harm."