Horse Riding Evolution: Genetic Mutation Key to Domestication?

Two key gene variants may have ​made​ early ​domesticated ‌horses more tame‌ and ‌more physically resilient to‌ bearing ‍a ‌rider,⁤ researchers report August ⁤28⁢ in ⁢ Science.The resulting horses were among the most​ significant advances ⁤in Bronze Age ⁢biotechnology.

Ancient horse DNA suggests modern domesticated ‌horses originated in southwestern Russia more than 4,200⁢ years ago, Ludovic Orlando‌ and‌ his ​colleagues ⁣reported in ⁢2021. While this revealed ‍the where and​ when ⁤for the domestication of horses, says Orlando, a molecular archaeologist​ at the Centre for Anthropobiology and Genomics of toulouse in France, there were still unanswered questions about precisely what horse‌ genes changed in those early populations.

Orlando and a team of scientists from China‌ and Switzerland ‍analyzed the genomes — the full set of genetic instructions⁤ — ⁢from 71 horses from a range of breeds and time periods. The researchers focused ⁢on ⁣266 places in the horse genomes to track the history of ⁢these genes from the early domestication process onward. Of these, nine genes showed strong signatures of selection, meaning the traits they produced in the horses may have been⁣ targeted by human breeders.

Two of these genes were‍ particularly interesting as they showed heavy ⁤selection very early on in horse domestication. One gene, ZPFM1, influences anxiety levels⁣ in mice and overall ‍well-being in humans. ZPFM1 underwent strong selection some 5,000 years ago, suggesting that one of⁤ the⁣ first steps in ⁣horse domestication involved ‍making the animals tamer.

Another location‍ in the genome, near a gene called​ GSDMC, experienced strong selection ‌a⁢ bit later, ⁢between about 4,700 and 4,200 years⁣ ago. Mutations at ⁢this spot in ⁢humans are associated with chronic⁣ back conditions and pain. In​ horses, they ​are linked with body​ length-to-height ratio.The team ran experiments on⁤ mice genetically modified to have GSDMC inactivated, ⁢and found the mice‌ had straighter spines and ‌stronger forelimbs.

Orlando and his colleagues ‌think changes to GSDMC would have altered how ⁢horses⁣ move and bear weight, possibly ⁢making them more suitable steeds. Over just a few hundred ⁣years, a variant of this⁢ gene exploded‍ in frequency and went ⁤from barely detectable to⁤ present in almost all horses.

“That means people intended to put that variant more frequently in the population,” orlando ​says. Horses with the mutation had an estimated 20 percent more offspring than‍ those without. “When you see something like that,‍ you⁣ know you’re onto something ​that was really a game changer for horse biology.”

Rideable horses were also a pivotal shift for human​ societies,​ setting the stage for ‌ far greater mobility and changing the⁣ face of⁣ war​ and ‌transportation.

The findings are “a really⁣ resounding case of circumstantial evidence,” says Samantha Brooks, a​ geneticist at⁢ the University of Florida in Gainesville. “We know from ⁢our archeological record that we‌ can begin to see the ⁤types of changes that⁤ indicate these horses ‍were used during domestication and then we can​ together see these strong shifts in the genome itself at two very specific locations.”

While GSDMC appears critically⁤ important to the rise of horse riding, Orlando notes there ‌might potentially ​be other genes that were missed in their analysis,‌ or crucial cultural innovations — such as tactics​ for interacting⁣ with horses — ‌that didn’t ⁤leave their footprints in ⁣the genome.

Orlando ‍is ⁢interested in⁢ how particular⁣ genetic traits in​ horses may have fed into the success and development of horse-fueled steppe empires in Mongolia and china.

“We are sequencing a​ lot of those [ancient] horses to understand ​what kind of horses those societies and states ​developed to make the societies ⁣we read about in history.”