When humans first started domesticating wild horses around 5,000 years ago, their coats were likely closer to zebras' than the uniform browns we see today, a new study found.
The only wild horses that still survive today, which are known as Przewalski’s horses, are all Dun-colored. This pattern often includes zebra-like stripes on the legs and a characteristic stripe along the back.
But nearly all domestic horses aren't Dun-colored — they mostly have single-colored coats, without any fun stripes.
In the new study, researchers wanted to look at how horses' coat color might have changed with domestication.
So they analyzed the DNA of two horses: One that died 4,400 years ago, and another that died 42,700 years ago. They compared the ancient horse's coat-color genes to current zebras, and wild and domestic horses. The results were published December 21 in Nature Genetics.
The gene that causes Dun is dominant, so even if horses have only one copy of it, their coats are Dun-colored.
All of the zebras in the study had two copies of the Dun gene, and so did the Przewalski’s horses.
But most domestic horses didn't have any of the dominant Dun genes, the study reports.
Here's where it gets interesting, though. The uniform coat-colors of these domesticated horses seem to have cropped up just around the time we started using them on our farms.
The 4,400-year-old horse didn't have DNA that would suggest it was Dun-colored — it had neither copy of the dominant gene, just like today's domestic horses.
But going back further in horse evolutionary history, the 42,700-year-old ancient horse did have one copy of the dominant Dun gene, and was likely Dun-colored.
While these are only two data points, they suggest that the non-Dun genes (and uniform coat colors) existed before humans domesticated horses. But since the Dun genes are dominant, shaded and striped coats were likely more prominent in ancient wild horses.
The researchers speculate that humans likely selected and bred horses they domesticated to have uniform coats so they'd be easier to spot in the fields, without the Dun-colored camouflage that hides them.
They had to be able to find their horses in a field or forest to domesticate them, after all.
