Farming rewired Earth’s mammal communities after the Ice Age

Humans didn’t just outlast the last Ice Age; after it ended, we rewrote the script for the evolution of the world’s mammal communities.

Over the past 10,000 years, the rise of agriculture and livestock farming has reshaped natural animal communities just as profoundly as the Pleistocene extinctions that wiped out mammoths, giant sloths, and other megafauna.

A new study traces 50,000 years of animal history and shows a clear pivot point. During the Late Pleistocene, mammal communities fell into recognizable patterns. These were determined climate zones and geographic barriers – mountain ranges, oceans, deserts.

After farming took hold, a small cast of domesticated species spread with people. This collapsed those biogeographic boundaries, making far-flung regions look unexpectedly similar.

“We can now see agriculture and hunting acting together as global forces that reorganized ecosystems,” said co-author John Alroy of Macquarie University. “That legacy still complicates conservation today.”

Mammal communities and the map of life

The research team, led by Barry Brook at the University of Tasmania, compiled species lists from hundreds of archaeological and paleontological sites spanning the last 50 millennia.

They compared two snapshots: the Late Pleistocene (ending about 11,700 years ago) and the Holocene (our current epoch).

In the Pleistocene, community composition mostly followed nature’s rules. Animals co-occurred in predictable ways along climate gradients, and big physical barriers kept faunas distinct. In the Holocene, that pattern breaks.

Wherever people farmed, the same handful of domesticated mammals show up again and again. These include cattle, sheep, goats, pigs, horses, and a few others. Their occurrence has nothing to do with the local climate or native fauna.

Domesticated mammals replaced wild ones

Across more than 350 sites, the team found that just 12 domesticated species appear at roughly half of them. This is an outsized footprint, given the thousands of wild mammals that existed.

Dogs and donkeys are part of the story, too. Chickens weren’t included in the core analysis because bird fossils are rare and inconsistent. Even so, they turned up at dozens of sites, mostly in Europe and the Middle East.

These arrivals coincided with losses. Many wild species disappear from regional records soon after humans arrive. The pattern points to hunting-driven extinctions rather than a single, simultaneous climate shock.

Tracking ecosystems without maps

To make sense of so many sites, the authors developed “chase clustering,” a computer method that groups locations by how similar their species lists are, ignoring distance on the map.

That vantage point highlights what traditional, geography-first approaches can miss: human activity makes distant ecosystems converge.

In the Holocene clusters, domesticated mammals act like glue, linking sites that are thousands of kilometers apart.

As those same livestock became established across continents, the wild mammals that once defined regional character either thinned out or disappeared.

The result is a planetary remix. For example, communities in Europe and parts of Africa grow more alike after both adopt livestock domesticated in the Middle East.

The method also helps parse time. In region after region, the tight Pleistocene clustering begins to break apart.

What replaces it are looser, human-shaped groupings in the Holocene – a clear sign of ecosystems no longer bound by climate or geography alone.

Farming replaced lost wilderness roles

The late Ice Age extinctions hit hardest where native animals had little previous exposure to people – North and South America, Australia, New Zealand, Madagascar. But the study shows the story didn’t stop with mammoths and giant marsupials.

In the Holocene, agriculture produced a different kind of shake-up that continued to replace and homogenize faunas.

Intriguingly, when the big herbivores vanished, smaller wild mammals did not surge to fill the vacuum as some theories would predict.

In many places, livestock took their place ecologically, monopolizing grass and browse and crowding out native grazers and browsers.

Mammal communities varied

Human influence wasn’t uniform. Some regions – New Guinea and Sri Lanka are standouts – show relatively modest Holocene change in community composition.

Others saw dramatic turnover, with Europe, the Americas, Australia, and parts of Africa registering the largest mix of losses and gains.

History, climate, culture, and geography all shaped where agriculture spread early and intensively, and where it remained limited or later-arriving.

Still, the global arc is unmistakable: over roughly the past 10,000 years, humans oversaw a wholesale replacement of native mammal communities with a narrow set of domesticated lineages.

What this means for conservation now

If modern protected areas strive to safeguard “natural” communities, it matters that many of today’s ecosystems have been fundamentally reorganized for millennia.

In some of the hardest-hit regions – Australia and the Americas, for instance – national parks now lack more than half of the large native mammals that would likely have persisted, had human interference not occurred.

Alroy points to a striking Australian example. A single layer in Tight Entrance Cave (Western Australia) preserves fossils from 17 large mammal species.

These include the thylacine (Tasmanian tiger), the Tasmanian devil, the marsupial lion Thylacoleo, the giant herbivore Zygomaturus, an oversized wombat, and five species of short-faced kangaroos.

It’s an assemblage that bears little resemblance to anything living there today – a window onto a baseline that has been missing for thousands of years.

Mapping change in mammal communities

The takeaway isn’t nostalgia for a frozen past; it’s clarity about baselines. The “naturalness” many of us imagine is already a post-extinction, post-agriculture world.

Recognizing that helps guide rewilding, manage livestock near protected areas, and identify native species that can be restored.

It also gives researchers a fresh tool. Because chase clustering ignores geographic distance, it can be applied to other fossil datasets to detect human fingerprints – or the lack of them – across time and space.

That, in turn, can help disentangle hunting impacts from climate swings, and domestication effects from other cultural shifts.

The big picture is both sobering and useful. Humans didn’t just add cows and sheep to the landscape; we redrew the map of mammal communities. Any plan to protect what’s left – and revive what’s gone – has to start from that reality.

The study is published in Biology Letters.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–