Pedigree Pseudo-science
by Roger Lyons
Eugenics was a pseudo-science that sprang up in the latter half of the 19th century to account, among other things, for why the English upper-class was so superior to other populations and why other people were so–well, lower class. That social class could be a heritable biological property was not the only question begged by eugenics. Its foundational principle was “purity of blood,” and, as spurious as that concept has proven to be, it continues to pester thoroughbred pedigree understanding.
It now masquerades as the idea that all good racehorses result from crossing “close genetic relatives.” In a way, that’s a very easy sell because close genetic relationships are even more ubiquitous in thoroughbred pedigree than in the pedigree of eugenically bred, 19th-century, upper-class Englishmen. In fact, close genetic relatives are crossed in the breeding of inferior horses just as frequently as in the breeding of superior ones. In any event, it’s a distinctively eugenic concept insofar as the “blood” relationship itself is treated as the cause of superior performance.
The harm of eugenic analysis is that it misses the point of what really matters in thoroughbred performance–the heritable traits that constitute a well-formed individual. It’s quite true that similarities among thoroughbred horses are ultimately attributable to shared genetic background, but that same background also gives rise to traits which, in the composition of an individual, may be utterly incommensurable with one another. Indeed, the genetic background a mare shares with a stallion might regularly contribute traits that conflict with traits that are regularly contributed by that stallion.
It’s not necessary to pinpoint conflicting traits in order to confirm their existence. Some of those traits may not even be visibly evident, but their existence can be inferred from the statistical trace they leave behind. Let’s just arbitrarily select an ancestor to see how it works. Let’s take Nijinsky II.
Much has been made of the close genetic relationship between Nijinsky II and Storm Bird, and there are, of course, a lot of stallions that have Storm Bird in their ancestries–particularly with the popularity of his son Storm Cat. So, the consequences of mistaking Storm Bird’s close genetic relationship with Nijinsky II for evidence of a broad benefit when crossing these two ancestors are far-reaching. Accordingly, the eugenic approach to pedigree evaluation often goes very far wrong.
It takes Forest Wildcat 24 mares with Nijinsky II in their ancestries to get just one superior runner from the alleged genetic affinity between Storm Bird and Nijinsky II. His record stands at three superior runners from 71 mares. Giant’s Causeway requires 18 mares in descent of Nijinsky II to get one superior runner, with his record of 6/108. In North America Tale of the Cat goes through 32 mares with Nijinsky II in their ancestries in order to get a single superior runner (3/97).
Most other stallions that have Storm Bird in their ancestries have only an average strike rate with mares in some descent of Nijinsky II. A few actually do respond favorably to the traits conferred by Nijinsky II, but, since the genetic relationship in question is constant, all of that is explainable only in terms of variations in the way the offspring of different stallions are affected by the contribution of those traits.
Despite the close genetic relationship, traits regularly conferred by Nijinsky II conflict with the performance of foals by as many stallions in descent of Storm Bird as benefit from Nijinsky II’s contribution. The idea that crossing these two ancestors has an absolute value, precisely because of the genetic purity they represent, is nothing other than eugenics disguised as genetic analysis.
The message to breeders is that they should beware of pedigree prognostication that says a certain stallion with Storm Bird in his ancestry “should” like mares with Nijinsky II in their ancestries because of the close genetic relationship between those two ancestors. It all depends on the traits the individual stallion routinely brings to the match. Having “the right blood” made a lot of difference in 19th-century English society, but on the racetrack it’s all about having “the right stuff.”