Reproductive biologists have been working for decades to solve one of the great mysteries of human fertility: why do women produce all the eggs they will ever have while still in the womb, only to have most of those eggs die off before birth, and many more before the woman reaches puberty?

Jonathan Tilly, chair of the biology department at Northeastern University in Boston, was among those drawn to studying this enduring puzzle. But what he found instead was evidence of a fundamental flaw in the basic tenets that govern our understanding of the female reproductive system. If successful, his research could open the door to the most radical advancement in infertility treatment since in vitro fertilization was invented nearly 40 years ago.

When Tilly examined the ovaries of mice, he noticed that their eggs were dying much faster than the overall egg count would suggest. The mice appeared to be producing new eggs, and were doing so by a process that no one really understood.

Tilly’s team began researching the role that stem cells play in the process. Chinese researchers later identified a specific type of stem cell located in the ovarian tissue.