Spotted Horses
© The Bridgeman Art Library/Getty Images; Thomas Hackmann (insert) No flight of fancy? DNA evidence suggests that spotted horses (inset) probably existed at the time cave artists were painting them, for example, 25,000 years ago at this cave in Spain.

About 25,000 years ago, humans began painting a curious creature on the walls of European caves. Among the rhinos, wild cattle, and other animals, they sketched a white horse with black spots. Although such horses are popular breeds today, scientists didn't think they existed before humans domesticated the species about 5000 years ago. Now, a new study of prehistoric horse DNA concludes that spotted horses did indeed roam ancient Europe, suggesting that early artists may have been reproducing what they saw rather than creating imaginary creatures.

Archeologists have found more than 100 painted caves depicting at least 4000 animals in Europe, nearly all of them concentrated in southern France and northern Spain. They include France's Chauvet Cave, dated to at least 32,000 years ago and featuring the earliest known cave art, as well as the roughly 15,000-year-old caves of Lascaux in France and Altamira in Spain. Nearly a third of the animals in painted caves are horses; and nearly all of the horses are rendered in brown or black, similar to the bay or black colors of today's horses.

But a small number of caves, including 25,000-year-old Pech Merle in southern France, feature horses painted white with black spots. Some archaeologists have argued that this leopardlike pattern was fanciful and symbol laden rather than realistic. Indeed, in a 2009 analysis of DNA from the bones of nearly 90 ancient horses dated from about 12,000 to 1000 years ago, researchers found genetic evidence for bay and black coat colors but no sign of the spotted variety, suggesting that the spotted horse could have been the figment of some artist's imagination. Although researchers can only speculate on what prehistoric artists were trying to express, hypotheses range from shamanistic and ritualistic activities to attempts to capture the spirit of horses and other animals that ancient humans hunted.

But in a new paper published online today in the Proceedings of the National Academy of Sciences, the same team reports finding that spotted horses did indeed exist around the time that cave artists were doing their best work. The researchers, led by geneticists Arne Ludwig of the Leibniz Institute for Zoo and Wildlife Research in Berlin and Michael Hofreiter of the University of York in the United Kingdom, analyzed DNA from an older sample of 31 prehistoric horses from Siberia as well as Eastern and Western Europe, ranging from about 20,000 to 2200 years ago. They found that 18 of the horses were bay, seven were black, but six had a genetic variant - called LP - that corresponds to leopardlike spotting in modern horses. Moreover, out of 10 Western European horses estimated to be about 14,000 years old, four had the LP genetic marker, suggesting that spotted horses were not uncommon during the heyday of cave painting.

If so, the team argues, prehistoric artists may have been drawing what they saw rather than creating imaginary creatures. Prehistoric horses came in at least "three coat color[s]," Ludwig says, "and exactly these three [colors] are also seen in cave paintings. Cave art is more realistic than often suggested."

As for why the spotted phenotype became more rare after 14,000 years ago, the team points out that some modern horse breeds with two copies of the LP gene suffer from night blindness, which would have made prehistoric horses more vulnerable to predators. The researchers speculate that the gene might have been beneficial during the ice age, when a white spotted coat could serve as camouflage in snowy conditions, but later became rare and disadvantageous until rediscovered by modern horse breeders.

Jean Clottes, France's premier cave art expert, agrees that cave artists may have painted horses as they saw them, although he argues that such realistic depictions of horses do not rule out possible symbolic meanings. "In [cave] art you find both naturalism and a departure from it," Clottes says. In the case of the Pech Merle spotted horse, for example, he points out that "the big dots were not only on top of the horses but all around them. This would probably mean that some special importance was attached to the dots rather than a simple wish to render them realistically."

Marsha Levine, an expert in prehistoric horses at the University of Cambridge in the United Kingdom, also thinks that the symbolic aspects of cave painting cannot be shunted aside. "Horses have potent symbolic meanings in all the cultures where they are found, including ours."