Because of the Thoroughbred’s value in racing as well as the general athletic ability that made it useful as an “improver” or desirable outcross, population numbers of the breed continued to increase through the 18th and 19th centuries.

ancestors, but their accomplishments in terms of number of starts, length of the course, estimated maximum and average speed, number of heats run and placements. To this, modern pedigrees add conformation photographs.

The operative term in the above paragraph is “accurately.” Unfortunately, even though the rule in Thoroughbred breeding has from the beginning been that mares must receive live cover, supposedly witnessed by honest and reliable persons, errors have been common. The circumstances are easy to imagine--everything from large farms having similarlooking mares, to simple misrecording, to deliberate deception for economic gain. In 2002, Emmeline Hill, PhD, and colleagues in the genetics lab at Trinity College in Dublin, Ireland, published a study based on maternal DNA (mtDNA) that uncovered probable errors in Thoroughbred pedigrees as officially recorded in the General Stud Book. Using tissue samples from hundreds of living Thoroughbreds, the researchers discovered “confusions” in the identity of certain foundation mares. In some cases it appears that the same animal was known by or recorded under two different names; in others, a mare other than the one given credit appears to have been the actual dam.

These confusions have profound implications, and not just for those who base multimillion-dollar purchase decisions on “tail female” ancestry. A fundamental rule in the study of biological populations is that, because their alleles represent all the variability within the gene pool, early ancestors---the “founder population”---determine the maximum number of alternative alleles in subsequent generations. Unless new blood is added---and in the case of the Thoroughbred, it has not been added to any significant degree in England, America or anywhere else since the beginning of the 18th century---the gene pool of the founder population will disproportionately leverage the capabilities and appearance of the breed.

Because of the Thoroughbred's value in racing as well as the general athletic ability that made it useful as an “improver” or desirable outcross, population numbers of the breed continued to increase through the 18th and 19th centuries. Thoroughbreds were shipped to all English colonies, including those in America, Canada, New Zealand, Australia and South Africa. They went to Mexico, Argentina, Arabia and Japan. It soon became evident that some method of sorting through the hundreds of colts offered at auction would be helpful, and several methods were tried. In 1895, Bruce Lowe, an Australian pedigree researcher, published Breeding Horses by the Figure System, which became the basis for many high-dollar purchases and breeding decisions. Taking the complete list of winners of the oldest English classics---the St. Leger Stakes, Epsom Derby Stakes and Epsom Oaks---Lowe grouped them by tail-female descent, tracing their lineages back to founder mares who lived in the late 17th century. Tabulating the total number of wins for each lineage, he found that the