I am updating this thread, which had 3 parts, and which I wrote back in 2013. (part 1, part 2, part 3).
I stumbled across a very interesting blog post [by Maju in his blog "For what they were… we are": Horse genetics (autosomal DNA)] which mentions the following paper: Genetic Diversity in the Modern Horse Illustrated from Genome-Wide SNP Data, Jessica L. Petersen et al, Published: January 30, 2013 https://doi.org/10.1371/journal.pone.0054997.
The Parsimony tree from this paper is pictured below (from the paper and with Maju's comments):
As you can see the branches closest to the root of the tree are the Latin American breeds from Puerto Rico, Peru and Brazil, followed by the Iberian breeds.
Maju's comment was revealing: "Ignoring by the moment the Latin American breeds, which stem directly from the root of the tree, the oldest division is between the Iberian breeds (Lusitano, Andalusian) and all others, which in turn split in two groups, both scattered in Europe and Asia (different parts of Asia however). This would seem to confirm the dual origins theory.
However there are two more elements to consider: on one side the Northern Iberian breeds (apparently even older than the Southern ones, per Warmuth 2011) are not being considered here.
The other element to ponder is the most strange position of the three Latin American breeds. As there were no horses in America at the arrival of Europeans, the origins of such anomaly must be in the Old World, meaning probably that these breeds retain genetics of even older populations. These could be the already mentioned Northern Iberian breeds but they are said to have some admixture from Berber horses (or Barb) as well and this population (argued to be very old) has not been subject to any genetic study as of now."
The point is that these Latin American breeds appear to be even closer to the asnine root than their alleged Iberian forebearers, that is, they are even "older" than the European breeds that are their ancestors. How come?
A recent paper by Ludovico Orlando et al., (Tracking Five Millennia of Horse Management with Extensive Ancient Genome Time Series Cell, vol 177:6 P1419-1435.E31, May 30, 2019 DOI:https://doi.org/10.1016/j.cell.2019.03.049) also noticed that there was a very basal Iberian breed, now extinct in the lineage of modern horses:
"We find that two extinct horse lineages existed during early domestication, one at the far western (Iberia) and the other at the far eastern range (Siberia) of Eurasia. None of these contributed significantly to modern diversity."
Below is a tree from Ludovico Orlando's paper. The pink branch at the top is the "ancient" Iberian lineage, followed by the Siberian one in pale blue:
However Orlando's paper does not have the DNA of American horses -logically because his team was studying domesticated horses, and that happened in Eurasia not America.
Could local "native" American horses, of the original American equine stock have mixed with later evolved Iberian horses brought by Portuguese and Spaniards to the Americas?
This would explain their position as more ancestral in the tree.
The interesting point is the "gait" gene. The Spanish and Latin American horses have a special gait.
Horses have gaits, they trot, gallop, canter and walk. But some breeds have another natural gait that is very peculiar (The rider appears motionless in the saddle, and there is no perceptible up and down motion of the horse's back); watch this video with the gait of a Peruvian Paso Fino horse (yes, it is one of those mentioned further up as a Latin American breed).
The Peruvian Paso Fino is one of many gaited horses. This is due to the DMRT3 "gait" gene, which (see source): "...must have diverged from a common ancestral sequence within the last 10,000 years. Thus, the mutation occurred either just before domestication or more likely some time after domestication and then spread across the world as a result of selection on locomotion traits".
Petersen's paper (mentioned further up) also noticed this: "It thus seems that the genetic variant associated with the gait phenotype arose well before the separation of breeds.", and notices that not only Iberian horses and Latin American ones are gaited, so are the Icelandic horses but these, "Instead of clustering with the other gaited breeds, the Icelandic clusters with the Shetland" suggesting a separate origin for this group, a branch that probably split from the original group carrying the mutation.
The gait trait is found all over the world -humans took their horses with them- in almost half the breeds tested and at "a frequency ranging from 1% to 100%" Worldwide frequency distribution of the 'Gait keeper' mutation in the DMRT3 gene, M. Promerova et al., Animal Genetics, vol 45:2 April 2014 P 274-282 DOI: 10.1111/age.12120). Some believe that it has been artificially selected for, by human domestication, as riders prefer this type of gait.
The ancient Asian Przewalski's horse does not carry this mutation, and although some suggest an English origin ca. 800 AD for the mutation, it was present in Spain over 2000 years ago because Roman naturalist Pliny the Elder (23–79 AD) wrote that horses from what is now Asturias in Northern Spain moved both legs on the same side alternately and did not trot.
In the Americas, apart from the Latin American horses mentioned above, the North American Indian's appaloosa breed also has a particular gate known as the "shuffle" (see appaloosa shuffle video). This horse is better known for its spotted coat, which was favored by the Natives.
A global distribution map of the DMRT3 mutation (from Promerova et al.)
As you can see no Southern South American (i.e. Caballo Criollo Argentino or Chileno) were sampled.
Considering that it originated at least 10 Kya, and is found in America and Eurasia, it is very possible that this mutation arose in the original American horse stock and spread across Eurasia. The Spanish horses brought to America by the conquistadors mixed with native horses that also carried the mutation hence Latin American horses with 100% levels of this gait gene.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2019 by Austin Whittall ©
Dear Austin, fantastic! I have never believed horses went entirely extinct in the Americas. I have also found suspect comments that native south Americans had "never seen horses" before the conquistadors arrived. Perhaps, they had not seen horses for a considerable number of millennia due to the megafaunal extinctions due to hunting. I can also imagine that due to the 90% reduction in human populations that much native knowledge went unrecorded. Remnant horse populations must, if they existed have been very sparse and localized.
ReplyDeleteOn that point, I recall reading some years ago that, some Californian baha ppopulations of wild horses could not be accounted for whatsoever. Maybe there were native and/or admired horse populations down to the 1800's? NeilB