In archaeological sites across southern France and Spain, researchers have analyzed thousands of animal teeth dating back 8,000 years. These remains, especially molars from sheep and goats, show the profound changes that domesticated animals have undergone.
A new study from the University of Montpellier reveals that sheep and goats, despite being herded together for millennia, followed very different evolutionary paths. Their teeth suggest that sheep became more diverse in size and shape, while goats remained relatively stable.
The difference, scientists say, comes down to how humans bred and used them.
Parallel Lives, Different Outcomes
The study, published in Philosophical Transactions of the Royal Society B, relies on a detailed analysis of 2,980 third lower molars from archaeological and modern sheep and goats. The team used a method called geometric morphometrics, which allows researchers to measure and analyze shape with remarkable precision. By applying this technique, they tracked how the teeth of each species changed over six cultural periods, from the Neolithic to the present day. Teeth are a valuable tool in archaeology because their shape is strongly influenced by genetics, less affected by environmental factors, and exceptionally well-preserved in buried remains..
The patterns were clear: sheep evolved with greater morphological diversity; they came in a greater variety of shapes and sizes. Meanwhile, goats remained relatively uniform.
“Distinct patterns emerge,” the authors write. “Sheep exhibit greater variability likely reflecting selective breeding for diverse purposes. Goats, in contrast, show greater uniformity.”
Even when the two species lived side by side, under the same environmental pressures, their evolutionary trajectories drifted apart. This divergence became most pronounced during the Middle Ages, coinciding with another change.
A different 2025 study found that around the year 1000 AD, domesticated animals like sheep, pigs, and chickens increased in size, whereas wild animals such as deer, foxes, and rabbits shrank. For wild animals, this was due to environmental changes (such as shrinking forests and intensified hunting). At the same time, domesticated animals came under tighter human control, bred more deliberately and systematically for productivity.
But why were goats and sheep so different?
Goats v. Sheep
Humans obviously didn’t select animals for their tooth shape. But the shape and size of teeth reflect broader selective pressures. When people bred sheep for larger bodies or specific skull shapes, the shape and size of molars changed as well. This was easily visible in sheep, which over thousands of years were selectively bred for meat, milk, and especially wool.
“Sheep have long been a pillar of the economy of many agro-pastoral societies,” the authors note. “This diversity of uses has driven a varied breeding history, leading to diverse morphologies adapted to various functions across time and regions.”
But the goats’ stability over time has puzzled researchers. Why didn’t they change more?
Goats, often stigmatized in pre-modern Europe for their ability to damage trees and graze indiscriminately, were sometimes restricted by law. In the 18th century, bans on free-grazing goats became widespread in France and other parts of Europe.
“Restrictions led to a reduction in the number of goat herds in certain regions,” the researchers note. That, in turn, may have suppressed morphological diversity.
When goats were grown, they were mostly used for milk. In many places, they were the livestock of the poor, often referred to as “the poor man’s cow.” They were hardy and adaptable, prized for their resilience more than their productivity. And their evolutionary story reflects that restraint. Essentially, sheep were grown for different purposes and artificial selection took different routes. For goats, it was one single purpose.
Another factor could be genetics. The study found that goats started with less variation in tooth shape than sheep, which may indicate a narrower genetic base or less selective breeding in early populations. This could have contributed to their relatively stable morphology over time.
And there is also the matter of intention. Breeders often invested more effort into refining sheep breeds for different purposes. By the modern era, France alone had nearly 50 recognized sheep breeds—and only 19 goat breeds.
Ultimately, the history of sheep and goats reveals how people have shaped animals—and been shaped by them. It reflects changes in farming, trade, and culture over thousands of years.
“Understanding the long-term interplay between human societies, environmental changes, and animal morphology is a fundamental question in evolutionary biology,” the researchers write.
