Horse running through field

What Linebreeding Really Is

by Roger Lyons

Most people think of inbreeding and linebreeding as two different things–inbreeding as a duplication of ancestors within four generations and linebreeding as a duplication of ancestors outside of that generational distance. Consequently, inbreeding is considered more intense than linebreeding because it involves less generational distance from the new individual.

What geneticists mean by linebreeding, however, has nothing to do with generational distance, and I know Blood-Horse pedigree columnist Les Brinsfield will back me up on this. It’s formed by the cross of two or more ancestors that share relatives on both sides of their ancestries. It’s what’s sometimes called crossing close genetic relatives. The generational distance of these ancestors from the new individual is irrelevant. The most intense form of linebreeding, in fact, consists in breeding a mare to her full brother. Clearly, linebreeding is a specialized form of inbreeding.

Well, then, if that’s what linebreeding really is, why is it that you can go to commercial breeding sites all over the internet and find it defined incorrectly–as a function of generational distance?

First, it’s important to understand that pedigree has no place in the science of inheritance. It has nothing whatever to do with genetics or its terminology. It was created out of whole cloth in the middle of the industrial revolution as part of an institutional structure for the new pure-breeding model. This was a time, don’t forget, when naturalists all over Europe, including Charles Darwin well into the 19th century, were preoccupied with exploring the biological frontiers of hybrid breeding–of crossing different varieties.

Besides wanting to see how weird a pigeon could look, they were interested in where to draw the lines between species. They had spirited debates in the Royal Academy about whether species difference should be inferred from the infertility of offspring, on the one hand, or, on the other hand, the inability of manifestly differing parents to reproduce at all. Hybrid breeding of English racehorses had been the dominant approach earlier in the 18th century, but the new pedigree breeding was at best tangential to prevailing, early 19th-century scientific interest.

At mid-century when Darwin was focused on how species adapt to their environments, the English Jockey Club had its hands full trying to adapt the racing environment to unanticipated changes in the population of pedigreed horses–and in such a way as to sustain the pretense that the horses were actually getting better in some absolute sense. Meanwhile, successive generations of horsemen since the first half of the 19th century have complained that the horses are not what they used to be, and they’ve been right all along.

Historically, the emergence of pedigree is understandable only from the standpoint of its commercial utility. Its form of development has been oriented, first and foremost, toward limiting the size and regulating the commercial value of living populations. The changing conditions of racing that at any given time reflect the thoroughbred population’s capacity for performance, the forms of genetic representation, typographical conventions, statistical formulations, cataloguing styles, pedigree analysis, and the terminology in which thoroughbred horses are discussed all comprise the system of signifying practices we call pedigree.

What does it all signify? It very convincingly signifies commercial value even if it’s not that good at predicting performance.

The new sense of pedigree, as represented by the English Stud Book, had much to do with the emerging industrial values of efficiency and scale, but it was also a form of commercial packaging. For the most part, science is welcomed to the party only at times when commerce has run so far afoul of biology that something needs to be fixed.

It’s not surprising, then, that linebreeding would be understood one way in a system of practices whose purpose is to represent its measurable effects and quite another way in a system whose purpose is to invest it with commercial value. Accordingly, linebreeding is a salient technique in the packaging of pedigree. Because inbreeding has a bad name in the world at large, commercial breeders, whether of dogs, cattle, whatever, don’t want to say the animals they’re selling are inbred. Instead, they say their animals are linebred, and they’re careful to make sure the breeding fits the definition that’s been especially adapted to the commercial interest in pedigree. It’s really just inbreeding packaged to sell.

To their credit, thoroughbred breeders are not so squeamish about inbreeding, but the commercial motives underlying pedigree so forcefully distort language and sense that the perception of linebreeding as a specialized–and often more intense–form of inbreeding has been almost hopelessly suppressed.

2 comments to “What Linebreeding Really Is”

  • Greg writes:

    Linebreeding as a means to limit the stud book in order to control the marketplace, right? Though my favorite image is of those weird pigeons.

  • Roger Lyons writes:

    Greg, I was taking some comic license there. Actually, a lot of the pigeon breeding was done with performance as an end. Darwin was an avid breeder of pigeons and was quite an expert at it. He refers to his experience breeding pigeons quite a lot in Origin of Species to illustrate principles of inheritance, and it’s clear that there was an aesthetic aspect to it. “Weird” is not the most historically accurate characterization I could have made, but I’m glad you like it.

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