The 2015 Kentucky Derby field is unthinkable without the 1964 winner -- and the beaten favorite in 1953

A thought experiment: imagine if every current NBA player were descended from Wilt Chamberlin, NFL players traced back to Johnny Unitas, and Ted Williams featured prominently in MLB players' genealogies. 

That's the case in Thoroughbred racing, where a few prepotent patriarchs hold sway -- as amply illustrated by the 2015 Kentucky Derby field.

Every contender descends from the 1964 Kentucky Derby hero Northern Dancer. And all of the top 21 (as of this writing) are inbred to Northern Dancer to one degree or another. Unbeaten Dortmund and Dubai shipper Mubtaahij boast no fewer than five crosses of Northern Dancer in total.

Watch the diminutive Northern Dancer hold off favorite Hill Rise in a time of 2:00, a record until Secretariat lowered it to 1:59 2/5 in 1973:

 

Although Northern Dancer didn't sire a Kentucky Derby winner himself, he became a phenomenal sire of global import, and thus continues to exert an enduring influence in pedigrees. His direct male-line descendants include four Derby winners (Ferdinand in 1986, Sea Hero in 1993, Charismatic in 1999 and Big Brown in 2008), but Northern Dancer often appears in other segments of the pedigree.

Representatives of Northern Dancer's sire line in the 2015 Derby are Dortmund (by Big Brown), Carpe Diem (by Giant's Causeway), El Kabeir (by Scat Daddy), Firing Line (by Line of David) and Tencendur (by Warrior's Reward).

Interestingly, Carpe Diem, El Kabeir and Firing Line are all descendants of Storm Cat, who established one of the most successful branches of the Northern Dancer male line. Despite that compelling resume, however, the Storm Cat branch has yet to record a Derby success.

All of the other 2015 Derby hopefuls can point to Northern Dancer elsewhere in their family trees. To put it another way, if Northern Dancer had never been born, this year's Derby field is literally unthinkable.

In fact, Northern Dancer's very existence depended on a twist of fate. His dam, Natalma, was training for the 1960 Kentucky Oaks when she sustained a knee injury. Connections decided to breed her and see if she got in foal.

Natalma was accordingly bred to Nearctic on a late cover -- and conceived Northern Dancer. The rest was history.

But Natalma brings another element to the Northern Dancer story. She was a daughter of the great Native Dancer, the "Gray Ghost," who came within a head of retiring undefeated from 22 career starts.

Native Dancer's lone loss came in the 1953 Kentucky Derby, where he lost position after being bumped on the clubhouse turn. As one observer reportedly said, jockey Eric Guerin "took that horse everywhere on the track but the ladies' room." Native Dancer tried to recover with a sustained rally down the stretch, only to fall agonizingly short of front-running longshot Dark Star: