The historical record on different lines of descent in the Thoroughbred shows that the winnowing out of male lines has gone on from the beginnings of the breed.
Article by Jay Hovdey: There is good reason the memory of Hall of Fame mare Gallorette bubbles to the surface at this time each year. It’s not because she was a champion, with 21 wins and 20 seconds in a career of 72 starts, or that she retired in the autumn of 1948 with record earnings and a collection of victories over first-class male competition.