Sacrifice of ancient horses gives clues to their domestication
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Sacrifice of ancient horses gives clues to their domestication

September 5, 2019

Around 5.5 thousand years ago, the Botai people in Northern Kazakhstan began riding and milking horses. This was the beginning of horse domestication, which allowed humans to travel much faster, connect to vast territories, and develop advanced warfare. Since then, horse domestication has transformed civilization, but how exactly has it transformed the horse? Recently, researchers sequenced the genomes of ancient horses, from 4.1 to 2.3 thousand years old. 13 samples come from the royal burial sites of Scythians, nomads who ruled much of Central Asia during the Iron Age. The Berel site is a rare snapshot of a horse population. 11 samples–all from the same generation. Sacrificed the same day as part of a funeral ritual, and almost perfectly preserved in permafrost. These samples tell us a lot about Scythians and their horses. First, the genomes show that the horses in their herds had a variety of coat-colors. Scythian horses carried diverse mutations relating to: Some of them had gene variants found in today’s fastest racing horses while others had gene variants associated with stamina. Researchers found 121 genes selected by Scythians, including a large number involved in the development of the legs of horses. It seems Scythian breeders selected for strong legs. Examination of the bones from the burial site and other Scythian remains confirm this finding. By comparing ancient genomes with present day genomes, researches came away with new insights on horse domestication and animal domestication in general. Scythian horses had a variety of y-chromosomes, which means male lineages in the first 3 thousand years of domestication were diverse. Modern samples however show that breeders seemed to use less and less of a variety of males, up to the point that today’s horses all carry virtually the same y-chromosome. This tells us that the horse population has collapsed within the last 2300 years. which resulted in a reduction of horse genetic diversity at the whole genome scale. During this same time period, breeding practices must have lead to the introduction of harmful mutations, because modern horses show an abundance of these mutations while Scythian horses don’t. Looking at the changes in horse genomes also gives support for a domestication hypothesis involving neural crest cells. Because these cells develop into many different tissues and cell lineages, changes in them might explain why many domestic animals share a group of traits like floppy ears and various coat colors. So studying the genomes of Scythian horses is starting to bring these ancient animals to life, but it’ll take make many more samples from all along the timeline and across the globe to tell the whole story of horse domestication.

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