In a set of experiments involving mice, Chinese researchers have shown for the first time that adult mammals can harbor primitive cells capable of becoming eggs and producing offspring. Their finding challenges the assumption that female mammals are born with all of the eggs they will ever produce. The news raises hopes that we could ultimately delay a woman's biological clock by stimulating cells to produce eggs again or by banking egg-producing cells for later use. Larry Mantle finds out more about this new research from fertility expert Dr. Richard Paulson.