Monday, September 05, 2005

Great horses of history.....   posted by Razib @ 9/05/2005 11:27:00 PM

There are reports that over in England they are going to be extracting and analyzing the DNA of great race horses. My first thought is that I am skeptical that Gulf Arabs have not been funding this line of research in secret for years. And of course, being American, I wonder when someone will get to the great Secretariat. A documentary on ESPN about 3 years ago presented an interview with a veterinarian who found out during the post mortem that Secretariat's heart was twice the median size! It seems likely that this physiological abnormality was responsible for his racing prowess. One important point to note is that there was a sharp regression among Secretariat's offspring, only a few had any competitive success and none came anywhere close to his virtuosity. This shouldn't surprise us, if you consider speed a phenotype one would imagine that if it is not 100% heritable than extreme phenotypes like Secretariat would not persist. But I doubt that a horse like Secretariat can be spoken of in such a fashion, his phenotype was way outside any normal range of variation, so I don't think a breeder's equation applied to him. It seems likely that Secretariat was simply an Ace of Spades genetically speaking, a combination of alleles resulted in his survival and expression of his freakish phenotype. One negative aspect of sexual reproduction is that extremely "fit" genetic combinations are disrupted. I don't know what Secretariat's record as a stud horse was, for example the number of healthy foals per copulation, but it wouldn't surprise me if many of the mares miscarried fetuses who had large hearts but lacked their sire's felicitous genetic arrangement.1

1 - One can conceive of all sorts of modifier or epistatic effects going on in the background resulting in Secretariat's peculiar phenotype. Or perhaps it was a developmental wrong turn which ended up saving the fetus' life. Or perhaps it was something strange in environment. In any case, his offspring were bound to regress.