Improbable traces his female line back to one of Darby Dan's foundation mares, the Polynesian matron Banquet Bell. One of the exclusive club of mares who have produced two American champions, Banquet Bell bred both 1962 champion older female Primonetta and 1963 champion 3-year-old male Chateaugay to covers by 1956 American Horse of the Year Swaps. Primonetta in her turn proved an equally splendid broodmare, throwing Grade 1 winners Prince Thou Art and Cum Laude Laurie (both by Hail to Reason) and Grade/Group 2 winners Grenfall and Maud Muller (both by Graustark). The Kentucky Broodmare of the Year for 1978, Primonetta also produced Grade 3 producer Sunshine O' My Life (by Graustark), but her branch of the family has failed to breed on since then.
The task of maintaining Banquet Bell's family into future generations instead fell to Primonetta's My Babu half sister Luiana, who proved a first-rate broodmare in her own right by giving birth to 1974 American champion 3-year-old male Little Current (by Sea-Bird; a useful sire), multiple Grade 1 winner Prayers'n Promises (by Foolish Pleasure), and Grade 2-placed stakes winner Water Dance (by Nijinsky II). Prayers'n Promises, in turn, produced French Group 2 winner Nabeel Dancer (by Northern Dancer) and is the second and third dam of Grade 3 winners, while Water Dance is the second dam of Grade 3 winner Magic Storm and the third dam of Grade/Group 1 winners Drill, Lachesis, and Satono Aladdin.
Luiana's Roberto daughter Darbyvail was a much lesser race mare than her half sisters, winning just two of 13 starts, and she produced only one stakes winner during her broodmare career, Grade 2-placed Turkish Tryst (by Turkoman). That was enough to maintain her name, however, as Turkish Tryst produced 2007 King's Bishop Stakes (USA-G1) winner Hard Spun. The son of Danzig has been a quite useful sire since his retirement, his 59 stakes winners including last year's Grade 1 winners Spun to Run, Hard Not to Love, and Out for a Spin.
Our Rite of Spring, a Stravinsky half sister to Hard Spun, was only a minor stakes winner on the track and last sold for US$5,000 at the 2017 Keeneland November mixed sale, in foal to Noble Mission. There was justification for this, given that Our Rite of Spring had failed to produce anything worth writing home about after breedings to a series of better-proven sires. Nonetheless, the old dictum that "the family is more important than the individual" appears to be well supported by her 2009 A.P. Indy daughter Rare Event, a decent winner who came up with Improbable as her first foal. Rare Event has since produced the 2017 Quality Road filly Redemption Day, who has been unplaced in two starts; Snake Doctor, a 2018 colt by Oxbow who has yet to start; and a 2019 colt by Cross Traffic. She had no produce for 2020.
In spite of his obvious talent, Improbable still appears to be a step or two behind the best of the American older male division in what may be one of the deeper such groups seen in recent years. But let him get into a scenario where he can make free use of his best weapon---his high cruising speed---and he is likely to be dangerous in any company. His successes, in turn, should help his close female relatives to continue getting access to good sires, helping to keep Banquet Bell's memory---and her genes---alive and well.