A new review paper by Pablo Librado and colleagues in the October issue of Genetics tells the story of how the modern horse came to be. They track the genetic changes that led from wild horses living on the Eurasian steppes 5,500 years ago to the many highly specialized breeds of domestic horse that exist today.
Modern horses have been shaped into distinct breeds with different talents and specialties. Compare a racing thoroughbred with a draft horse like a Clydesdale —they’re extremely different animals now, but they both descend from the same ancestral group of wild horses. Comparing the DNA variation of all different kinds of domestic horses and their only living wild relative, Przewalski’s horse, can reveal the genetic changes that occurred during domestication. Librado and colleagues emphasize that another crucial tool used for tracing the horse lineage is ancient DNA, which is extracted from bones of animals that have been dead for thousands of years. The oldest successfully extracted DNA came from the skeleton of a wild horse that lived in the Yukon between 560,000 – 780,000 years ago. Such samples are especially important because there are very few wild horses left alive, and modern horse breeding practices have obscured the genomic signature of early domestication qualities like geography. Thanks to data from ancient DNA, geneticists have learned that a previously unknown group of now-extinct wild horses were also ancestors to modern horses.
Remarkably, the majority of Y-chromosomes carried by modern domestic horses can be traced back to just a few stallions. This could be because only a few males were originally used in domestication, but it could also result from carefully controlled modern breeding practices where a single male sires a huge number of offspring. The ultimate cause of this very low Y-linked diversity is still debated, but strict selective breeding has almost certainly contributed. In contrast, a much larger number of females than males contributed ancestry to domestic horses. According to Librado and colleagues, it seems that wild mares were continuously introduced into human-controlled herds throughout the process of domestication.
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Modern horses have been shaped into distinct breeds with different talents and specialties. Compare a racing thoroughbred with a draft horse like a Clydesdale —they’re extremely different animals now, but they both descend from the same ancestral group of wild horses. Comparing the DNA variation of all different kinds of domestic horses and their only living wild relative, Przewalski’s horse, can reveal the genetic changes that occurred during domestication. Librado and colleagues emphasize that another crucial tool used for tracing the horse lineage is ancient DNA, which is extracted from bones of animals that have been dead for thousands of years. The oldest successfully extracted DNA came from the skeleton of a wild horse that lived in the Yukon between 560,000 – 780,000 years ago. Such samples are especially important because there are very few wild horses left alive, and modern horse breeding practices have obscured the genomic signature of early domestication qualities like geography. Thanks to data from ancient DNA, geneticists have learned that a previously unknown group of now-extinct wild horses were also ancestors to modern horses.
Remarkably, the majority of Y-chromosomes carried by modern domestic horses can be traced back to just a few stallions. This could be because only a few males were originally used in domestication, but it could also result from carefully controlled modern breeding practices where a single male sires a huge number of offspring. The ultimate cause of this very low Y-linked diversity is still debated, but strict selective breeding has almost certainly contributed. In contrast, a much larger number of females than males contributed ancestry to domestic horses. According to Librado and colleagues, it seems that wild mares were continuously introduced into human-controlled herds throughout the process of domestication.
- More Here
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