Great Schism

The Great Schism was an event that befell the planet Gallifrey long before the Gallifreyans took their position as Time Lords. It involved a war between the forces loyal to Rassilon and the female priesthood of the Pythia. The outcome of the war was the defeat of the ruling matriarchy and their banishment from Gallifrey but not before the Pythia cursed the Gallifreyan's with sterility. This led to a change in their reproduction with the creation of the Looms as their woman were no longer capable of giving birth to offspring. (NA: Lungbarrow)