Horse Domestication Explained in New Genetic Study

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Horses revolutionized human civilization but little was known about their domestication until a recent study explained the genetic components. The ancient partnership built empires, revolutionized trade, and eased transportation. It was a mystery how this sensitive creature came to trust people but now, the genetic record fills the gaps left unsatisfied by archeological discoveries.

Humans domesticated modern equines 5,500 years ago and started selective breeding almost immediately. This technique is well-known with all types of domestication, plant or animal, and not a surprise to discover. However, questions remained regarding the development of some traits over others to get the numerous breeds people enjoy today.

The questions arose because these are flight animals that likely deeply feared humans. Ancient communities almost hunted them to extinction until it was realized that their speed, strength, and agility could serve societal needs. Functions and tasks for may have been limited at first and then expanded as desired characteristics developed.

The study, lead by geneticist Ludovic Orlando of the Natural History Museum of Denmark and published in the Proceedings of the National Academy of Sciences, explained the evolution from food source to vital element in transportation, warfare, and agriculture. It compared three groups of DNA: the Przewalski’s horse (only surviving wild species), ancient skeletons discovered in Siberia, and domestic horses. The ancient DNA dated from 16,000 to 43,000 years ago, well before domestication.

Finding comparable DNA for wild species was essential for the genetic study to adequately explain differences arising from domestication. Most wild species existing today, including the American Mustang and Australian Brumby, are feral descendants of domesticated stock. One wild species, the Tarpan, has been extinct since 1909.  The Przewalski’s horse is a controversial comparison as there are different theories of their relationship to domestic species.

Current surviving wild species proved to be a valid comparison when taken in context with the genetic profiles of ancient species. Re-sequenced DNA revealed that modern equines carried genetic markers relating to behavior, fear response, speed, and build that are not present in Przewalski’s horses or the ancient DNA.

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Przewalski’s Horse in Captive Breeding Program

Dr. Orlando uncovered 125 genetic markers showing the desirable traits for domestic breeds. One group emphasized physical characteristics like muscle development, physical shape, cardiac structure, and other desirable traits for riding, pulling or hauling. The second group addressed cognitive functions including intelligence, socialization, fear response, and ability to bond with humans.

Results also revealed the cost of domestication including the ill effects of inbreeding and mutations in order to get the desired traits. Previous studies on other domesticated animals and plants revealed the same occurrence and show horses were not immune. Markers also showed that sometime in history, societies started restocking their  herds by introducing wild stock, leaving modern varieties with some wild markers.

Genetic confirmation of how horses arose to their domesticated personas still faces controversy after the release of this study. Comparing ancient DNA to current profiles can be problematic as there is a chance that horses existing 5,500 did not have the same traits as the DNA from horses living 16,000 to 43,000 years ago. The goal and hope is that eventually scientists will have access to DNA existing closer to the time horses first started their partnership with humans.

By Jocelyn Mackie

Sources:

PNAS Open Access

University of Copenhagen (Press Release)

Reuters

Main  Photo by Paul Dunleavy – Flickr License

Inside Photo by John Vetterli – Flickr License

 

 

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