The Evolution of the Horse: Interview with Dr. Marcos Imberti

By: Natalia Imberti Posted: 13/11/2024

Introduction: The relationship between humans and horses has existed for centuries and has been essential for both species' survival. Thanks to horses, people could shorten distances and connect villages. They were also significant allies during times of war and conquest. Understanding the origins and evolution of horses helps us appreciate how they developed social and cooperative skills. To explore these aspects, we interviewed Dr. Marcos Imberti, a Professor and PhD in Biological Sciences from the University of Buenos Aires. Together with biologist María Susana Rossi, he co-authored Educating Darwin, a scientific novel aimed at presenting updates to the theory of evolution in an educational way.

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GETTING TO KNOW MARCOS IMBERTI

1. What inspired you to study biology?

Well, beyond my interest in biology itself, what motivated me most was the teachers I had in my youth. They taught me to view the world in a more interesting way.

2. You specialized in evolutionary biology; why did you choose this field?

The choice developed over time. What fascinated me most about evolutionary biology was its perspective on the world and our place in it, connecting history, philosophy, and culture.

3. You have been a professor for years. What do you consider most important for future biologists?

The most important thing is not to lose sight of our place in the world, as well as to maintain critical thinking at all times.

4. Your family works in horse breeding and equestrian tourism. How has this influenced you?

From a young age, I had the privilege of being close to horses, and I’ve developed a deep respect and admiration for their beauty and behavior.

THE ORIGIN OF HORSES

5. It is believed that the earliest ancestors of the horse lived about 50 million years ago. Can you tell us more?

Yes, the ancestors of modern horses date back between 50 and 55 million years. These early animals, very different from today’s horses, were small and had various differences in dentition and body structure.

6. From these early ancestors, which parts of the horse’s body have changed the most?

The most significant changes have been in the teeth and body size. Horses evolved from small, browsing animals to larger ones adapted to grazing.

7. All horses come from a common ancestor. When did they start differentiating by breed?

Today’s horse breeds emerged as a result of human domestication. While some natural differentiation likely occurred, the breeds we know today are mainly the result of human-driven artificial selection.

8. What is the oldest identifiable horse?

The closest common ancestor to all modern horses likely lived around 100,000 years ago. This ancestor reproduced with other horses but left the most descendants to this day.

9. In your book Educating Darwin, you discuss changes in aspects of Darwin’s Theory of Evolution from its inception to the present. What are the major advances since then?

There have been many advances, especially in theories that complement natural selection. If I had to highlight a few, I would mention the inheritance of acquired traits and epigenetics. Darwin didn’t know about DNA but spoke of the inheritance of innate characteristics. Today, we know that acquired characteristics can also be passed down temporarily. Another important advance is our expanded view of evolution, understanding that it doesn’t occur only through natural selection but also through many other factors, such as historical contingencies and random events.

10. Could you explain more about epigenetics and how it influences evolution?

Sure. Epigenetics studies changes in gene expression that don’t alter the DNA sequence but can be inherited temporarily. This means that some traits acquired by an individual due to their environment can be passed down for a generation or two, although they may eventually disappear. This opens a new perspective on how organisms adapt to their environment and how certain traits can be inherited without changing the DNA.

11. Returning to horses, you mentioned that the ancestors of modern horses lived around 50 million years ago. How did they evolve from those small herbivores to the horses we know today?

Horse evolution was gradual but consistent. The earliest horses were small, about 40 centimeters tall, and had multiple toes instead of a single hoof. Over millions of years, their limbs elongated, some toes atrophied until only the center remained, forming the hoof we see today, and their teeth adapted to eating tough grasses instead of leaves and twigs. These changes allowed them to survive in the open habitats and plains that expanded during that time.

12. Regarding size, why do you think horses have increased in size throughout evolution, while other animals tend to reduce in size?

Many groups of animals have shown a trend toward increased size throughout evolution, especially vertebrates. In horses, increased size was likely favored by the environment, allowing them to access more resources and avoid predators. Larger animals often succeed in certain environments because they can move more quickly and access a greater range of resources.

13. How did domestication impact horse evolution?

Domestication was a crucial shift in horse evolution. Through artificial selection, humans began to breed horses for various purposes, such as agricultural work, transportation, and war. This led to the development of breeds with specific characteristics, like stronger horses for field work or faster horses for travel. This human-driven selection allowed certain traits to become established in different breeds of horses.

14. What do you find most surprising about horse evolution?

What surprises me most is how a small, multi-toed herbivore adapted to swampy environments evolved into the strong, fast animal we know today. Horses adapted to diverse environments, and their relationship with humans has been key to their evolution. Their evolution involved not only physical changes but also behavioral ones, making horses essential companions to humans over thousands of years.

15. Horses belong to a group of equines that also includes zebras and donkeys. Can you differentiate some evolutionary traits among them?

Evolutionarily, little is known in detail. However, we know that all three species (zebras, horses, and donkeys) share a trend toward increased body size. The ancestors of all three were smaller in ancient times. As for current differences, we mainly see variations in behavior and habitats. For example, zebras live in Africa and have complex social hierarchies, while donkeys, native to Africa and Asia, are more solitary.

DOMESTIC VS. WILD HORSES

16. When did horse domestication begin?

It was believed to have started around 4,000 BC on the Asian steppes. However, new research suggests domestication may have occurred in different places and times, possibly much earlier, for purposes such as transportation, agriculture, and war.

17. What happened to wild horses that weren’t domesticated? Are there any surviving species?

It was once thought that there were wild horses that had never been domesticated, such as the Przewalski horse in Mongolia. However, recent research suggests these horses may have been domesticated at some point and then released. So, today, there may be no truly wild horses—only horses that have "re-wilded."

18. What physical changes occurred in horses due to domestication?

The changes were many and varied. Each human group domesticated horses with different goals, such as speed or strength. This resulted in significant morphological diversity but with reduced genetic diversity, similar to what happens with dogs.

BREEDS AND HORSE CROSSBREEDING

19. There are many horse breeds. What is the process for forming new breeds?

The process of creating breeds involves first defining an objective, like breeding a fast horse. From there, animals best suited to that objective are selected to reproduce. This process is repeated over generations to achieve the desired breed.

20. How has the evolutionary process influenced breed differentiation?

Once humans intervene, it’s difficult to separate natural evolution from artificial selection. Human-driven artificial selection acts faster than natural evolution, which takes thousands or millions of years.

21. Can different horse breeds be grouped biologically according to common characteristics?

Yes, just like with humans, a family tree can be created for horse breeds. Some breeds are more closely related to each other, and this can be represented in an evolutionary tree.

22. Do you think artificial selection has influenced the evolution of horses more than natural selection?

Absolutely. Artificial selection has been the main driving force in the evolution of domesticated horses, as humans select specific traits based on their needs. Natural selection still exists, but human intervention has played a much more significant role in the formation of the breeds we know today.

23. What genetic differences are there between wild and domesticated horses?

Genetically, domesticated horses have less diversity compared to groups that were never domesticated or had minimal human intervention. Artificial selection tends to reduce genetic variability by focusing on very specific traits within a small group of animals.

FUTURE OF HORSES

24. So, what is the future of horses in today’s society?

I believe the future of horses lies mainly in entertainment, equestrian tourism, and sports. Although machinery has replaced horses in agricultural work and transportation, the emotional and recreational connection people have with horses remains strong. The experience of horseback riding, enjoying their company, and using them in sports like equestrianism or polo will continue to be relevant.

25. You mentioned horse breeds; is there any official regulation for creating new breeds?

Yes, there are regulations established

CLOSURE:

We thank Dr. Marcos Imberti for sharing his insights, helping us to better understand the evolution and cultural impact of horses. His perspective reminds us of the unique connection between humans and horses—a relationship that continues to grow in the realms of sports, tourism, and recreation.

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