The age of menopause doesn't seem to have changed much in the last few thousand years. Records from ancient Egypt and Greece indicate that menstruation ended when a woman was around 50 years old. Before that we don't really know, as a woman was unlikely to live much longer than 50.

We do know that a woman is born with all the eggs she's ever going to have, and that the menopause indicates the depletion of all those eggs. Or this was known until recently.

Research done in the 1950s showed that the number of eggs in the ovaries declines with age. Most are killed by their own body, in a natural cell-death process called apoptosis. At the fifth month of gestation the female fetus has around 6 million oocytes (egg cells), but at birth the ovaries contain only 1 to 2 million. In childhood, many more oocytes degenerate.