In a study that had never been attempted by previous scientists, Makova and her team analyzed the complete mitochondrial genomes from four female lineages that currently survive within the Przewalski's horse population. They first determined that the mitochondrial genomes of two of the maternal lineages actually were identical, thus narrowing the genetic pool to three maternal lineages. Then, they tested their data against the prevailing hypotheses about the genetic history of Przewalski's horse. According to one hypothesis, Przewalski's horse evolved first, with the domestic horse later evolving as a derivative species. According to another hypothesis, the genetic story is the opposite: the direct ancestors of the domestic horse were first on the evolutionary scene, with Przewalski's horse evolving and forming a new species later. According to the former hypothesis, the divergence of the two species had to have occurred around the time of horse domestication -- about 6,000 to 10,000 years ago.
"My team discovered that neither scenario is likely," Makova said. "Instead, our data suggest that Przewalski's horse and the domestic horse are much more distantly related. In fact, they probably shared a common ancestor as far back as 160,000 years ago, long before horse domestication. This is a major shift in our understanding of the history of Przewalski's horse." To bolster their conclusions, the team also sequenced a portion of the Przewalski's horse's nuclear DNA -- the part of the genome passed to offspring from parents of both sexes. In addition, they sequenced a portion of the genome of a third species known as the Somali wild ass, the wild progenitor of donkeys. Makova explained that adding this information allowed her team to "calibrate the molecular clock of horse evolution," thus narrowing the window of time for sub-species divergence and confirming her team's suspicions that horse domestic
|Contact: Barbara Kennedy|