Horses were domesticated long after dogs, cattle and pigs.
However, once humans started riding and milking horses, and once they
controlled their reproduction, the whole face of history would no longer be the
same. In particular, the horse transformed the way we made war, the way we
travelled the world and the way we transported goods.
An international team of 121 scientists led by Prof Ludovic
Orlando and in collaboration with Barbara Wallner from the Institute of Animal
Breeding and Genetics at Vetmeduni Vienna have been reconstructing the complex
history of domestic horses. They have not only tracked changes in the horse
genome from the very early stages of domestication but also followed the legacy
of important equestrian civilizations until the revolution of modern agronomy.
The work brought together a multidisciplinary research team,
involving archaeologists, geneticists, and evolutionary biologists across 85
institutions around the world.
By studying genome-wide data from 278 ancient equids
spanning the last 42,000 years, the research team gained insights into how ancient
equestrian civilizations managed, exchanged, and bred horses. Their studies revealed
a vast loss of genetic diversity as well as showing the existence of two
extinct lineages of horses that failed to contribute to modern domestic
animals.
Antoine Fages, leading author of the study, which is
published in the journal Cell, undertook most of the molecular work. He says:
“With the new dataset generated, horses become the animal species with the
largest number of ancient genomes characterized after humans. This extensive
dataset provides unprecedented information on how the animal looked like in the
past but also on how herders exchanged, mixed and selected their horses in the
course of human history.”
The scientists discovered that a previously unknown lineage
of horses was present in Iberia until at least 4,000 years ago. This lineage no
longer exists and contributed only marginally to the genome of modern horses
around the world. The same is true for another lineage of horses that roamed
the vast territory of Siberia in the Upper Paleolithic and until the third
millennium BCE, from the northern end of Yakutia to the Altai mountains range.
The work, thus, demonstrates that even though only two main lineages of horses
exist today – the domestic horse and the Przewalski’s horse, the available
diversity of lineages was considerably larger by the time humans first
domesticated the animal.
Pablo Librado, who coordinated the bio-informatic analyses,
states: “Iberia has a long-standing tradition of horse breeding and a cave art
record featuring many horses. It was, thus, proposed as one possible domestication
centre for horses. Our new genome information reveals for the first time that a
yet undescribed horse lineage was roaming in the peninsula some four to five
thousand years ago. They however disappeared and are not the ancestors of the
modern horses in Iberia and more generally around the world.”
Previous work from the Orlando team demonstrated that
Przewalski’s horses represent the descent of a lineage that was first
domesticated in Central Asia during the Copper Age, some 5,500 years ago.
Modern domestic horses, however, were found to descend from another genetic
lineage that spread across Eurasia during the early Bronze Age, by the end of
the third millennium BCE. The new genetic data generated now help track how
this new lineage has developed since then and diversified into the hundreds of
modern breeds that we know today.
The research reveals that the 7th-9th century AD was marked
by a major transition in Europe. So much so that the only horse breeds
genetically close to the horses populating the main continent during the Iron
Age and Gallo-Roman times can only be found now in some British Isles and in
Iceland. These were probably brought to these islands by the Norse people.
In mainland Europe, however, another horse group tracing its
origins in the Persian Sassanids became so popular that it provided the source
of most modern breeds found across the planet. This influence was not limited
to Europe but also extended to Central Asia.
In order to identify the factors that underlie the
increasing success of this type of horse, the researchers scanned the genomes
of Byzantine horses, which descended from this new type. They found signatures
of positive selection in no fewer than 11 genes involved in the development of
the body plan This suggests that the morpho-anatomical traits first acquired in
Persian Sassanid horses became increasingly appreciated and spread out
following the Persian wars and the Muslim expansion.
In addition to detecting changes in the horse
morpho-anatomy, the researchers could leverage their extensive genome
time-series to track the frequency of specific gene variants underpinning key
equine traits, such as coat coloration, speed and gait. The authors reveal that
several gene variants associated with racing performance increased in frequency
during the last 1,500 years. The first occurrence of the DMRT3 ambling gene
variant was found in a specimen that lived in the late Middle Ages, and
increased in frequency in the past centuries. This suggests that locomotor
changes in speed and gait types were selected mostly during the last
millennium.
But the most dramatic change the researchers identified was
not in the far distant past, but in the modern era. Orlando adds: “Our most striking
finding was that the overall horse genetic diversity was relatively steady for
most of the last four millennia. However, it dropped significantly during the
last few centuries, at a time coincident with the development of close studs
and modern breeding techniques”.
This is perhaps the most important lesson of this work: the
modern world we live in can hardly give an idea of the diversity of domestic
resources that were available in the past, be it even a few centuries ago.
For more details, see:
Tracking Five Millennia of Horse
Management with Extensive Ancient Genome Time Series
Fages, A.,and others.
Cell.(2019) Vol 177, p 1419-1435.e31,
