Scientists trace the origin of modern horse

The horse transformed human history - and now scientists have a clearer idea of when humans began to transform the horse.

Around 4,200 years ago, one particular lineage of horse quickly became dominant across Eurasia, suggesting that's when humans started to spread domesticated horses around the world, according to research published Thursday in the journal Nature.

There was something special about this horse: It had a genetic mutation that changed the shape of its back, likely making it easier to ride.

"In the past, you had many different lineages of horses," said Pablo Librado, an evolutionary biologist at the Spanish National Research Council in Barcelona and co-author of the new study. That genetic diversity was evident in ancient DNA samples the researchers analyzed from archaeological sites across Eurasia dating back to 50,000 years ago.

But their analysis of 475 ancient horse genomes showed a notable change around 4,200 years ago.

That's when a specific lineage that first arose in what's known as the Pontic-Caspian Steppe, a plains region that stretches from what is now northeastern Bulgaria across Ukraine and through southern Russia, began to pop up all across Eurasia and quickly replaced other lineages. Within three hundred years, the horses in Spain were similar to those in Russia.

"We saw this genetic type spreading almost everywhere in Eurasia — clearly this horse type that was local became global very fast," said co-author Ludovic Orlando, a molecular archaeologist at the Center for Anthropobiology and Genomics of Toulouse in France.

The researchers believe that this change was because a Bronze Age people called the Sintashta had domesticated their local horse and begun to use these animals to help them...