How have humans affected the development of horses over time?

We don’t often consider what a profound effect the humble horse has had on human history. Thousands of years ago humans domesticated horses, and in so doing revolutionised travel and trade, and the way they waged war against other nations. Through such activities, they also accelerated the geographic expansion of languages. Horses changed history in significant ways, but what effect have we had on these four-legged friends?

To answer this question, researchers recently constructed a genetic history of the domestic horse spanning 5 000 years. Their goal was to understand how humans changed horses to suit their purposes in the course of history. They found that human activities have in fact resulted in a significant drop in equine genetic diversity. Their study, conducted with partial support from the EU-funded project SYNTHESYS PLUS, is the first-ever attempt to apply DNA sequencing technology on such a large scale to a non-human organism.

More lineages discovered

The study’s findings point to a much more complex genetic history than previously thought. Besides the two horse lineages known today – the domestic horse and Przewalski’s horse – the researchers found evidence of two more, now extinct, lineages that existed in Iberia and Siberia some 5 000 years ago. However, these horses made a limited genetic contribution to the modern horse. “They are a sort of horse equivalent of what Neanderthals are to modern humans,” says Prof. Ludovic Orlando of project partner University of Copenhagen in a news release published on EurekAlert!

Persian influence and speed

An increasing affinity to Sassanid Persian horses was detected in Asian and European horse genomes after the 7th to 9th centuries. The horses that were common in Europe before this era are now only found in parts of Iceland, while today’s horses bear a greater resemblance to Sassanid Persian horses. This shows that Byzantine-Sassanid wars and the early Islamic conquests most likely had a significant impact on horse breeding. “It was a moment in history that reshaped the landscape of horses in Europe,” he explains. “If you look at what we today call Arabian horses, you know that they have a different shape--and we know how popular this anatomy has been throughout history, including in racing horses.”

Genes associated with elite racing and speed only rose in popularity in the last millennium, bringing about significant changes in the domestic horse. However, the biggest drop in genetic diversity has occurred in the last 200 years, as a result of modern breeding practices. “What we picture as a horse today and what we picture as a horse from a thousand years ago or two thousand years ago was likely actually very different,” says Prof. Orlando. “Some of those traits that we are most familiar with are only a modern invention, and in the last few hundred years, we have actually impacted the horse genome a lot more than in the previous 4 000 years of domestication,” he adds.

The SYNTHESYS PLUS (Synthesis of systematic resources) project is the fourth iteration of the SYNTHESYS programme. It brings together the European branches of global natural science organisations and their extensive collections in order to integrate and internationalise efforts to answer fundamental scientific questions about ecological, evolutionary and geological processes.

For more information, please see:
SYNTHESYS PLUS project website