A sweeping analysis of 50,000 years of fossil data reveals that human activities, particularly the advent of agriculture, have fundamentally reorganized mammal communities across the globe. The research, which draws on hundreds of archaeological and paleontological sites on six continents, demonstrates a dramatic shift from naturally-ordered ecosystems to a world dominated by a handful of domesticated species.
Before the rise of agriculture, mammal populations were structured by climate, geography, and natural barriers, creating distinct and predictable continental patterns. However, beginning around 10,000 years ago, this natural order was scrambled as humans spread across the planet, bringing with them a small number of livestock animals that would come to dominate ecosystems and erase long-standing zoological boundaries. This transformation, detailed in the journal Biology Letters, has had a lasting impact on biodiversity and presents ongoing challenges for conservation.
A World Shaped by Nature
During the Late Pleistocene, the geological epoch that ended around 11,700 years ago, the distribution of mammal species was a product of natural forces. Climate gradients, mountain ranges, and oceans acted as barriers, shaping the composition of animal communities. As a result, regions with similar climates tended to host similar assemblages of animals, creating a predictable pattern across the continents. This natural distribution meant that the mammal communities of Europe and Africa, for example, were distinctly different, each adapted to their specific environmental conditions.
The Great Scrambling
The dawn of the Holocene, our current epoch, marked a profound turning point. The development of agriculture and the domestication of animals triggered a wholesale reorganization of the world’s ecosystems. Researchers found that a small group of just 12 domesticated species began to appear in archaeological records across vast distances, fundamentally altering the composition of local mammal communities. This agricultural expansion acted as a powerful force, breaking down the natural boundaries that had separated animal populations for millennia.
The Dominance of Domesticated Species
The study identified a dozen key domesticated species that played an outsized role in this global transformation. These include cattle, sheep, pigs, and horses, which were found in roughly half of the global sites studied. Other impactful species included donkeys, goats, and dogs. The spread of these animals, facilitated by human migration and trade, meant that ecosystems thousands of kilometers apart began to share the same mammal species for the first time. Large grazers like cattle and horses were particularly influential, as their consumption of vast quantities of vegetation left fewer resources for native wild animals.
New Techniques for Understanding the Past
To analyze the vast dataset, the researchers employed a novel method called “chase clustering.” This technique groups fossil sites based on the species they share, rather than their geographical location. The results showed that, as agriculture spread, distant sites began to cluster together, linked by the presence of the same domesticated animals. For example, the introduction of livestock from the Middle East made the mammal communities of Europe and Africa more similar to each other than they had ever been. This clustering highlighted the homogenizing effect of human activity on a global scale.
A Varied Impact Across Continents
The study also revealed that the impact of humans on animal communities was not uniform across the globe. The Pleistocene extinctions, which occurred before the rise of agriculture, were most severe in regions where wildlife had not co-evolved with humans, such as the Americas, Australia, New Zealand, and Madagascar. In the Holocene, the agricultural revolution had its most profound effects in Europe, the Americas, Australia, and parts of Africa. In contrast, some regions, like New Guinea and Sri Lanka, experienced relatively little change in their mammal communities as a result of farming.
Lessons for Modern Conservation
The findings of this research have significant implications for today’s conservation efforts. Associate Professor John Alroy of Macquarie University, a co-author of the study, stated that “the study shows how agriculture and hunting combined as powerful global forces to reorganize ecosystems, which still creates conservation challenges today.” The research underscores that for the past 10,000 years, humans have been actively replacing diverse native mammal communities with a very limited set of domesticated species. According to lead author Professor Barry Brook, a conservation biologist from the University of Tasmania, this historical perspective is crucial for understanding the long-term drivers of biodiversity loss and for developing effective strategies to protect what remains of the world’s natural heritage.