The discovery, published Monday in the journal Proceedings of the National Academies of Science, "suggests that the painters in Pech Merle actually had spotted horses in their vicinity," said Kerstin Lindblad-Toh, a geneticist at the Broad Institute in Cambridge, Mass., who was not involved in the research. "It would appear as if they, at least in this case, were painting things they really saw."
A team led by Arne Ludwig, a geneticist at the Leibniz Institute for Zoo and Wildlife Research in Berlin, found that six of the ancient horses they sampled had a gene associated with the spotting pattern. All came from Europe. Four dated from the Upper Paleolithic era, like the Pech Merle paintings and ones at the famous complex of caves in Lascaux, France.
Ludwig said that based on the team's limited sample, it was impossible to estimate the exact proportion of horses that would have had the mutation 25,000 years ago. But, he added, "it couldn't have been rare."
The gene variant causes leopard spotting in horses by interfering with pigmentation. Horses with just one copy of the mutation usually have some variation on a white coat with colored spots.
That's a whole lot like the horses painted at Pech Merle, said study co-author Rebecca Bellone, a geneticist at the University of Tampa in Florida. The images suggest that leopard spotting extended far back in horses' genetic history, she added.
French archaeologist Jean Clottes, president of the International Federation of Rock Art Organizations, has argued that the paintings were shamanistic or religious in nature. He said that he was excited about the new research, but that it didn't change his mind about the depictions.
He noted that the ancient artists included dots both inside and outside the outlines of their horses.
"Painting (the dots) outside the horses was giving them a meaning or role other than purely descriptive," he said.
Ludwig, however, said that these ancient people probably would have paid close attention to characteristics of horses, including coat color, because many human cultures were based on hunting horses, the dominant large mammal species in Eurasia at that time. Ancient spotted horses "would have looked more or less like this - white with spots," he said.