New fossil research shows that humans have reshaped animal communities as extensively as the great extinctions of the Ice Age. The spread of farming and livestock scrambled natural ecosystems and left a lasting mark on wildlife across the globe.
The international study, published in Biology Letters, examined fossil records spanning 50,000 years on six continents. During the last Ice Age, mammal communities followed clear patterns shaped by climate zones and geographic barriers.
That balance shifted around 10,000 years ago, when the rise of agriculture allowed a small group of livestock species to travel with humans, breaking down natural boundaries.
“The study shows how agriculture and hunting combined as powerful global forces to reorganize ecosystems,” said Associate Professor John Alroy of Macquarie University, a co-author of the study. It “still creates conservation challenges today.”
Comparing past and present
The team compared species records from the Late Pleistocene, which ended about 11,700 years ago, with those of the Holocene, the epoch that followed. Lead author Professor Barry Brook, a conservation biologist at the University of Tasmania, said the work drew on species lists from hundreds of archaeological and fossil sites across multiple continents.
Map showing the distribution of domestic animals (sheep, goat, cattle and pig) in different parts of Europe and the approximate time of their appearance. pic.twitter.com/YFjbIcQWVj
— Nrken19 (@nrken19) February 22, 2025
The analysis revealed that only 12 domesticated species—such as cattle, sheep, pigs, and horses—appeared in nearly half of the global sites studied. These few animals dramatically altered the composition of mammal communities. “After farming began, just a handful of livestock species spread with humans and scrambled those natural boundaries,” Brook said.
Other domesticated species, including donkeys, goats, dogs, and chickens, also left a wide footprint. Large grazers like horses and cattle were especially influential because they consumed vast amounts of food, leaving fewer resources for wild species.
Breaking natural patterns
The researchers used a new method called “chase clustering” to group fossil sites by shared species rather than geography. The technique showed that domesticated animals created links between sites thousands of kilometers apart, while many wild mammals disappeared soon after humans arrived.
Humans were apex predators for two million years
“humans specialized in hunting large animals and were in fact hypercarnivores”
Humans ate meat and little else.
Only large animal extinction led to eating more plant foods and eventually, farming pic.twitter.com/IDNTJWWuSh
— P.D. Mangan Health & Freedom Maximalist 🇺🇸 (@Mangan150) August 2, 2024
Normally, nearby sites share animals because of similar climate and environment. Human activity broke that rule by spreading the same farm animals across distant regions. Europe and Africa, for example, became more alike once both adopted livestock from the Middle East.
Uneven global impacts
The impacts were global but uneven. Pleistocene extinctions hit hardest in places where wildlife had little evolutionary history with humans, such as the Americas, Australia, New Zealand, and Madagascar.
Later, agriculture caused the most upheaval in Europe, the Americas, Australia, and parts of Africa, while areas such as New Guinea and Sri Lanka saw relatively little change.
Ecosystems are not truly natural
The findings also challenge assumptions about post-Ice Age ecosystems. “When megafauna like mammoths disappeared, we expected the absence of competition for food,” Alroy said. “But this didn’t happen.”
He added that ecosystems have not been fully natural for at least 10,000 years. In the hardest-hit regions, national parks now lack more than half of the native large mammals that once lived there.
One excavation layer in Tight Entrance Cave in Western Australia contained 17 large mammal species—including thylacines, the Tasmanian devil, a giant wombat, and several extinct short-faced kangaroos—evidence of a community vastly different from anything seen today.
