Farming forever changed animal communities worldwide

Fossil records from six continents tell a clear story about how humans reorganized the animal kingdom during the Holocene era.

In a new study, researchers examined more than 350 fossil and archaeological mammal species spanning about 50,000 years to see how communities changed as people shifted from hunting to farming.

Before agriculture, mammal communities were shaped by climate and geography. During the last Ice Age, continents carried distinct sets of species that rarely overlapped.

Humans altered old patterns

Scientists refer to these broad patterns as biogeography, the study of how life is distributed by place and climate.

In the Late Pleistocene, oceans, deserts, and mountain ranges acted like natural filters, and species groups sorted into stable regional patterns.

The Holocene began after the Ice Age ended about 11,700 years ago. In this warmer epoch, people refined hunting and began farming, and these choices began to alter the old patterns.

This project includes John Alroy of Macquarie University (MQU), who studies long-term biodiversity change and helped analyze the data.

Hunting and farming during the Holocene

Once people began keeping animals, a small set of domesticated species moved with them.

The team reports that just 12 domestication events mattered most for mammals in the record, and those few livestock taxa appear at roughly half of the Holocene sites they analyzed, including cattle, sheep, pigs, and horses.

“The study shows how agriculture and hunting combined as powerful global forces to reorganize ecosystems, which still creates conservation challenges today,” said Alroy.

Scientific data confirms a shift

To avoid counting biases, the researchers used the presence/absence of species rather than raw bone counts. This is a standard approach in zooarchaeology that compares which animals show up at sites.

The team paired this with two clustering methods, one that respects geography and a second that focuses only on which species occur together.

The second approach, a composition-only algorithm, asked a simple question: If you ignore the map and look only at species lists, do far-flung sites still group like neighbors?

In Pleistocene layers, both methods recovered familiar continental groupings. In Holocene layers without domestic species, some of those groupings persisted, but the similarities weakened.

When domestic species were added back in, distant regions suddenly looked alike because livestock linked them. The algorithms grouped sites far apart based on shared cows, sheep, goats, pigs, and horses.

The impact of domesticated animals

Even a modest number of domestic species can reshape communities because they are abundant and eat the same foods as many wild animals.

Large ungulates like cattle and horses graze heavily, and in high numbers, they can monopolize plant resources that wild herbivores once used.

“All domesticated species had an impact, including donkeys, sheep, goats, pigs, and dogs,” said Alroy.

The study emphasizes that such effects add up when those species appear across continents.

Human impact on modern landscapes

Archaeological and ecological syntheses show that people have been altering landscapes for thousands of years.

A global analysis indicates that by about 12,000 years ago, most of Earth’s land had already been shaped by human land use.

Another global synthesis shows that land use intensified through the last several thousand years, with farming and herding becoming widespread well before modern times.

Those shifts laid the groundwork for the Holocene reorganizations seen in the new fossil analysis.

Farming reshaped animal communities

Some regions lost iconic megafauna during the late Quaternary as humans arrived. A broad overview links many of those losses to human pressure, which set the stage for later reorganizations under agriculture.

Turnover varied by place in the new analysis. In the Americas and Australia, the composition of mammal communities changed more than in many parts of Africa or parts of Asia.

For 34 locations with time series, the team compared lists from Pleistocene layers to Holocene layers near the same spot, typically within about 31 miles.

That approach tracks change at the local scale while still connecting those sites to the big picture.

Domestic species amplified similarities among faraway sites. Remove them, and the Holocene looks a bit more like the Pleistocene, but not entirely, because hunting and land clearing had already pushed many wild species out.

Parks and policy updates

Modern protected areas often sit within landscapes already reshaped by past choices.

“National parks in the hardest hit regions, such as Australia and the Americas, lack over half of the native large mammal species that would have been present if not for humans,” said Alroy.

That context matters when setting goals. Some places may need reintroduction plans or novel management because the original community is no longer achievable under present conditions.

A clear message from bones and bytes

The fossil record preserves a long-running experiment that people unwittingly ran. When small sets of domestic animals spread, they weakened old biogeographic boundaries and stitched far-apart places into similar community types.

The new analysis clarifies that pattern with code and careful curation. It also shows that even moderate changes in which species co-occur can shift the entire map of community similarity.

The study is published in the journal Biology Letters.

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