While domestic animals gradually became larger over the last 1,000 years, wild animal body sizes shrank. A new study conducted in Mediterranean France identifies one clear common denominator driving these opposing changes: us.
Humans are a major driving force of evolution on Earth, and this large new investigation led by University of Montpellier archaeologist Cyprien Mureau provides a stark example.
Using over 81,000 physical measurements of remains collected from 311 archaeological sites, Mureau and colleagues found domestic animals such as chicken and cattle increased in size over the last millennium, while wild animals, like foxes and deer, got smaller.
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Mureau and team also modeled environmental factors across 8,000 years, including climate, vegetation, and human land use. They found the opposing trends suddenly accelerated over the last 1,000 years, coinciding with booms in agriculture and urbanization.
As expanding human populations shrank and fractured the wilderness, the researchers explain, available resources became reduced. Combined with increased hunting, wild mammals and birds – herbivores and carnivores alike – were placed under increased selection pressures that caused them to shrink in body size as well as abundance.
Meanwhile, humans favored and therefore bred larger domestic animals for the products they provide. Larger sheep produce more wool; heftier cattle, more meat; bigger chickens, more eggs, and so on. Domesticated chickens now make up over three times the biomass of all wild birds combined.
"These findings … [highlight] … in the last millennium, the increasing impact of human activities," Mureau and team write in their paper.
Other recent studies have demonstrated unintended consequences of human activities changing the bodies of other wild animals. Puffins are miniaturizing, and the wingspans of cliff swallows are also shrinking. Many fishes are now 20 percent smaller thanks to overfishing, and their lifecycles are 25 percent shorter on average, too.
All this is a direct consequence of how humans exploit natural resources without foresight of future environmental impact.
A 2021 study found species that don't provide us with direct benefits are more likely to be the ones crucial for maintaining ecosystem stability – the same stability the species we do directly rely on require to continue existing. Even parasites can play an outsized role in balancing our ecosystems.
But only if we let them keep existing.
This research was published in PNAS.