Horse running through field

Deconstructing Blood Affinity

by Roger Lyons

In response to my last post, which was nothing more than an info-torial about the CompuSire online product, Byron “the straw man” Rogers posted the closing paragraph to a yahoo group. Here is the exerpt he posted:

“I’ve looked at too much good pedigree information to think there’s any such thing as a pedigree affinity, least of all in the sense suggested by those 200 stakes winners. All statistical blips are reducible to the function or dysfunction of certain traits within a very specific context of traits. Obviously, not all the experts agree with me on that, but here’s their little secret. The experts don’t understand pedigree any better than you or I do, especially when it comes to your mare. ”

That’s okay because I meant what I said. But Byron, always the dissembler, put that quote under the topic line “We all know nothing?”–knowledge in place of understanding. He threw the bone and then sat back to enjoy the feeding frenzy, and I was meant to be the bone.

Of course, I’m rescued by 2,500 years of western philosophy, in which the distinction between knowing something and understanding it is fundamental. That distinction is so ingrained that it routinely takes part in ordinary conversation. One can know the facts, but not understand them. In the context of an info-torial promoting an online pedigree information facility, it’s implicit that there’s a lot of pedigree information to be known, and it’s quite explicit that the experts know more of it than anyone else–precisely because, as I said, they use CompuSire online. Oops, Byron left that sentence out.

As the quote above indicates, I don’t believe the concept of pedigree affinity, or, alternatively, “blood affinity” meets a 21st-century standard of pedigree understanding. I’ll illustrate what I mean. The following facts drive that concept to the end of its 19th-century tether.

The stallion Distorted Humor is widely believed to have a powerful blood affinity with La Troienne. No doubt, much pedigree knowledge points to this. However, the more one delves into the facts, the more that idea deconstructs.

I count occurrences of ancestors within six generations of mares that have produced foals by a stallion. Some pedigree experts will say that’s not enough, but, when you use six generations for counting opportunity and six generations for counting the mares that produced superior runners by the stallion, then you will get valid strike rates.

The fact is that Distorted Humor’s strike rate with mares that have La Troienne within six generations is 19 superior runners from 130 mares (19/130), only slightly (but not significantly) above his overall strike rate.

Now, every pedigree expert knows that La Troienne mainly descends through daughters, with the exception of her son Bimelech, 1937 by Black Toney, and Bimelech descends mainly through daughters, the most notable exception being his son Better Self, 1945 out of Bee Mac, by War Admiral, but also others. Here are the facts.

With mares that have La Troienne descending through a female strain (daughters), Distorted Humor’s strike rate jumps to 17/90, which is significantly greater than his overall strike rate. However, with mares that have La Troienne descending through a male strain, he has the abysmal strike rate of only 2/40. So much for the blood affinity between Distorted Humor and La Troienne, but there’s more.

Keep in mind that’s counting only the times Bimelech occurs when La Troienne occurs within six generations. He has a lot more occurrences than that if you count the times he occurs within six generations when La Troienne is farther back. Even though Distorted Humor has a strike rate of 2/40 with male strains of La Troienne when she is within six generations of the mare, his strike rate with Bimelech alone within six generations overall is 14/125, only slightly below his overall strike rate (not statistically significant). Are the two sets of numbers relating to Bimelech contradictory?

Not if you distinguish Bimelech’s descent through sons and daughters. Among mares that descend from Bimelech through his daughters, Distorted Humor has the phenomenal strike rate of 9/54, but through males the strike rate with Bimelech is only 5/72, significantly below his overall strike rate. The culprit? Better Self, with which Distorted Humor has a strike rate of only 2/61. We must suspect that the problem is Better Self, specifically, because through Bimelech’s male strains Brookfield (1942) and Jabneh (1952) the strike rates are 1/6 and 4/29, respectively.

How far does the concept of blood affinity go toward an understanding of these numbers? Quite simply, it leaves us mystified.

As I’ve said before in this blog, these numbers are explainable only in terms of traits, and here’s but one dimension of the explanation. It’s grounded in theory of inheritance. Certain traits passed on by Better Self, so forcefully that they are conferred routinely, if not almost unexceptionally, by contemporary mares, are so at odds with the pedigree context of traits controlled by Distorted Humor as a sire that they negatively affect the performance of runners by him.

Another dimension, of course, relates to the traits that complement Distorted Humor’s influence, and La Troienne is certainly a prime source, but only through descendents that confer those traits, along with some traits they’ve picked up and passed on forcefully themselves.

Pedigree experts, it’s too late for 19th-century notions. Welcome to the 21st century.

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