Domestic animals have grown larger over time, while wild animals have generally shrunk, although not consistently across all species.

In a fascinating discovery, a recent study published in Philosophical Transactions of the Royal Society B has shed light on the evolutionary paths of sheep and goats over thousands of years. The research, led by a team of scientists, analysed the morphology of 2,980 third lower molars from both archaeological and modern sheep and goats.

The findings suggest that restrictions on goat herding in certain regions may have played a role in suppressing morphological diversity in goats. In contrast, sheep, which were selectively bred for meat, milk, and especially wool, display a greater variety of shapes and sizes adapted to various functions across time and regions.

The divergence between the two species became most pronounced during the Middle Ages. Goats, it appears, started with less variation in tooth shape than sheep, which may indicate a narrower genetic base or less selective breeding in early populations.

By the modern era, France alone had nearly 50 recognised sheep breeds, compared to only 19 goat breeds. This disparity is thought to be due to breeders investing more effort into refining sheep breeds for different purposes, leading to a greater number of sheep breeds compared to goat breeds.

Interestingly, the study found that goats were mostly used for milk, often referred to as "the poor man's cow," and their evolutionary story reflects a focus on resilience over productivity. On the other hand, sheep were selectively bred for meat, milk, and especially wool, which may have contributed to their greater morphological diversity.

The evolutionary trajectories of sheep and goats, despite living side by side under the same environmental pressures, have drifted apart. This finding underscores the profound impact humans have had on shaping animals and being shaped by them, reflecting changes in farming, trade, and culture over thousands of years.

The study used geometric morphometrics to measure and analyze the shape of the teeth. This method revealed clear patterns: sheep came in a greater variety of shapes and sizes, while goats remained relatively uniform.

Furthermore, a different 2025 study found that around the year 1000 AD, domesticated animals like sheep, pigs, and chickens increased in size, while wild animals such as deer, foxes, and rabbits shrank. This trend suggests that human intervention in animal breeding has played a significant role in shaping the physical characteristics of domesticated animals.

The history of sheep and goats, therefore, provides a compelling example of the long-term interplay between human societies, environmental changes, and animal morphology. Understanding this interplay is a fundamental question in evolutionary biology, offering insights into the complex ways in which humans have influenced the development of the animals we share our world with.

In pre-modern Europe, goats were sometimes stigmatized for their ability to damage trees and graze indiscriminately, leading to legal restrictions on free-grazing goats. This, combined with the focus on resilience over productivity in goat breeding, may explain the relative uniformity observed in goat morphology compared to sheep.

In conclusion, the study provides a fascinating glimpse into the evolutionary histories of sheep and goats, revealing how humans have shaped these animals and been shaped by them over thousands of years. The findings underscore the importance of understanding the long-term interplay between human societies, environmental changes, and animal morphology in the study of evolutionary biology.

Domestic animals have grown larger over time, while wild animals have generally shrunk, although not consistently across all species.