Like any revolutionary technology, domestic horses changed human society. The incredible speed and strength of these animals opened up new opportunities to spread trade, language, and culture. For thousands of years, horses have been helping build human society by pulling wagons and plows and carrying soldiers and travelers on their backs. Horse husbandry changed humanity, but along the way we changed horses too.
A new review paper by Pablo Librado and colleagues in the October issue of Genetics tells the story of how the modern horse came to be. They track the genetic changes that led from wild horses living on the Eurasian steppes 5,500 years ago to the many highly specialized breeds of domestic horse that exist today.
Modern horses have been shaped into distinct breeds with different talents and specialties. Compare a racing thoroughbred with a draft horse like a Clydesdale —they’re extremely different animals now, but they both descend from the same ancestral group of wild horses. Comparing the DNA variation of all different kinds of domestic horses and their only living wild relative, Przewalski’s horse, can reveal the genetic changes that occurred during domestication. Librado and colleagues emphasize that another crucial tool used for tracing the horse lineage is ancient DNA, which is extracted from bones of animals that have been dead for thousands of years. The oldest successfully extracted DNA came from the skeleton of a wild horse that lived in the Yukon between 560,000 – 780,000 years ago. Such samples are especially important because there are very few wild horses left alive, and modern horse breeding practices have obscured the genomic signature of early domestication qualities like geography. Thanks to data from ancient DNA, geneticists have learned that a previously unknown group of now-extinct wild horses were also ancestors to modern horses.
Remarkably, the majority of Y-chromosomes carried by modern domestic horses can be traced back to just a few stallions. This could be because only a few males were originally used in domestication, but it could also result from carefully controlled modern breeding practices where a single male sires a huge number of offspring. The ultimate cause of this very low Y-linked diversity is still debated, but strict selective breeding has almost certainly contributed. In contrast, a much larger number of females than males contributed ancestry to domestic horses. According to Librado and colleagues, it seems that wild mares were continuously introduced into human-controlled herds throughout the process of domestication.
Turning a wild animal into a domestic one that will tolerate humans involves a long process of selecting for traits like docility and friendliness. In the case of hard-working horses, desirable traits also included strength, endurance, and gait. This kind of selective breeding leaves a very clear mark in the genome. By comparing the genomes of modern domestic horses with very ancient domestic horses, geneticists were able to identify many genes linked to selected traits, including genes involved in coat color, skeletal structure, the circulatory system, and brain development and behavior.
Photo by Softeis via Wikimedia. The speed and stamina of modern racing thoroughbreds are the results of extensive artificial selection.
Similarly, comparing modern breeds can identify the genes that make each breed so different. Librado and colleagues describe how scientists have used this approach to identify gene variants involved in the superior racing ability of thoroughbreds and alternative gaits like those used in competitive jumping and dressage. Lesser known traits have also been investigated, like extreme cold tolerance in Yakutian horses. Their ability to survive harsh Siberian winters has been linked to genome regions that influence coat hair density and metabolism. Many domestic breeds suffer from a high frequency of inherited illnesses due to harmful gene variants being inadvertently selected alongside a beneficial trait. Genetic work has identified the genetic cause of muscle defects in Belgian draft horses, which interestingly enough may have once been a beneficial trait under the harsher conditions of its working past.
In many ways, understanding the history of horses is a vital part of understanding our own story. Yet many traditional horse breeds are now endangered, and unanswered questions about the genetics of horse domestication remain. In this review, Librado and colleagues urge haste to conserve this source of unique variation before it is too late.
Librado, P., Fages, A., Gaunitz, C., Leonardi, M., Wagner, S., Khan, N., Hanghøj, K., Alquraishi, S., Alfarhan, A., Al-Rasheid, K., Der Sarkissian, C., Schubert, M., & Orlando, L. (2016). The Evolutionary Origin and Genetic Makeup of Domestic Horses. Genetics, 204(2), 423-434. DOI:10.1534/genetics.116.194860
Katie is a science writer at GSA. She did her PhD work on the evolutionary consequences of genetic conflict in fruit flies at the University of Georgia.
View all posts by Katie Pieper »Read more in
-
In Memoriam: Ellsworth Herman Grell (1932–2023), a pioneer of Drosophila genome engineering and annotation
Ellsworth (Ed) Grell blessed the Drosophila community through three enduring legacies: as a pioneer of chromosome mechanics, as a primary organizer and synthesizer of genetic knowledge in Drosophila, and as a graceful mentor to those fortunate to have known him personally. Ed grew up in rural Nebraska, completed his undergraduate studies at Iowa State, and…
-
Congratulations to the #Fungal24 Poster Award winners!
We are pleased to announce the recipients of the GSA Poster Awards for posters presented at the 32nd Fungal Genetics Conference! Undergraduate and graduate student members of GSA were eligible for the awards, and a hard-working team of judges made the determinations. Congratulations to all! Felicia Ebot Ojong, The University of Georgia My research is focused…
-
Poster presentation tips for TAGC 2024
You’ve been selected to present a poster at The Allied Genetics Conference 2024 in March—you’ve celebrated, made plans to attend, now what? This is an exciting opportunity to showcase your research and engage with fellow members of the genetics community, so you want to make sure you’re prepared. We wanted to offer you some tips…
-
Maximize your TAGC 2024 experience
A guide to all that National Harbor & DC have to offer Are you joining us for The Allied Genetics Conference 2024 in March? Make the most of your #TAGC24 experience in National Harbor! We know the science will keep you busy, but you deserve to unwind and have some fun, so we’ve curated a…
-
Early Career Leadership Spotlight: Sarah Petrosky
We’re taking time to get to know the members of the GSA’s Early Career Scientist Committees. Join us to learn more about our early career scientist advocates. Sarah PetroskyMultimedia SubcommitteeUniversity of Pittsburgh Research Interest I am interested in understanding adaptation that has been happening recently in populations by dissecting the ways that genes underlying an adaptation…
-
TAGC 2024 Early Career Award Winners
GSA is pleased to announce the winners of the early career awards presented at The Allied Genetics Conference 2024. These awards are specific to particular TAGC communities and recognize early career scientists’ outstanding work on their respective research organisms. The awardees will present their talks in keynote sessions at TAGC 2024. Don’t miss the opportunity…
-
Preeminent geneticists recognized with revamped GSA Awards
In 2022, GSA’s Board of Directors launched an audit to review the five major awards conferred by the Society. Today, we are thrilled to announce the recipients of the reimagined GSA Awards, including the new Genetics Society of America Early Career Medal. The scientists honored this year are recognized by their peers for their outstanding…
-
Fly Board funds outreach programs to spread the word about Drosophila research
In 2020, the Fly Board voted to use part of its reserve fund to support efforts to increase trainee participation as well as equity and diversity in the Drosophila community. An awards committee decides how the money will be spent each year, and from 2020–2022, the committee posted a very broad call for applications from…
-
New members of the GSA Board of Directors: 2024–2026
We are pleased to announce the election of four new leaders to the GSA Board of Directors: 2024 Vice President/2025 President Brenda Andrews Professor, University of Toronto It’s an honor to continue my association with the Society by serving as Vice President of the Board of Directors. I have broad knowledge of the ongoing activities…
-
Parrot plumage study aids breeders and endangered natural populations
Yellow coloration is maladaptive in the wild but prized by breeders. People have long been fascinated with birds, which exhibit one of the widest ranges of coloration among vertebrates. Parrots, in particular, have captivated humans by their ability to mimic human speech and spectacular plumage. Brightly colored feathers are used primarily to attract mates, intimidate…
-
Early Career Leadership Spotlight: Sarah Gilmour
We’re taking time to get to know the members of the GSA’s Early Career Scientist Committees. Join us to learn more about our early career scientist advocates. Sarah GilmourMultimedia SubcommitteeStowers Institute for Medical Research Research Interest Questions of evolution have always fascinated me. I am extremely fortunate to be starting out my research career in a…