Only 10 horses have contributed >50% of the genes in the current generation of Thoroughbreds (Cunningham 1991). Four of these horses appear in the bloodlines of >30% of modern Thoroughbreds. The three horses shown are commonly called the pillars of the Stud Book.The Godolphin Arabian (top), born around 1725, contributed ∼14.6% of the genes in the present population of Thoroughbreds; the Darley Arabian (bottom left), born around 1688, contributed ∼7.5%; and the Byerly Turk (bottom right), born around 1690, contributed ∼4.8%. The fourth horse (not shown), the Curwen Bay Barb, born around 1699, contributed ∼5.5%. Six more horses add an additional 17.8%. (The paintings shown here are by Julie A. Wear. The Kentucky Derby Museum in Louisville has the Godolphin Arabian painting; the remaining two are in private collections.)