January 2005 -- In a breakthrough that sent shock waves through fertility clinics, Jonathan Tilly, a reproductive biologist at Harvard Medical School, released a study in March that suggests doctors may be able to boost women's supplies of eggs and help them bear children long after the normal onset of menopause. Biologists previously assumed that female mammals are born with a limited supply of eggs, which gradually declines with age. But the discovery of vast numbers of immature eggs dying in the ovaries of mice led Tilly's team to find what they claim are hidden ovarian stem cells that can sprout new eggs to replace vanishing ones.