The Human Factor

Since the Middle Ages, domesticated animals have been getting larger, while their wild relatives have been shrinking. 

That wasn’t the case more than 1,000 years ago, according to a new study. 

Instead, over most of the past 8,000 years, both wild and domesticated species evolved in synchronous and similar ways, underscoring how environmental and climatic changes played a huge role in shaping animal morphology, the French National Center for Scientific Research explained. 

Scientists say this change is due to humans. 

To arrive at this conclusion, researchers examined more than 80,000 bones and teeth from 311 archeological sites across southern France, spanning 8,000 years, recording their length, width, and depth, New Atlas added. 

The bones were from wild species such as foxes, rabbits, and deer, and domesticated animals like goats, pigs, cattle, sheep, and chickens. 

Researchers found a steady divergence over time, which sped up over the past 1,000 years.  

Wild species such as deer and foxes are believed to have gotten smaller due to an increase in hunting and the shrinking of their natural habitats. 

Meanwhile, the growing size of domesticated animals is linked to a significant human impact on environments, active efforts to increase productivity, and the development of selective breeding. Animals that could produce more meat, milk, wool, strength, or offer companionship were favored. 

These trends became especially evident around 1,000 years ago, when agriculture, urbanization, and trade networks were rapidly expanding. 

“From the Early Neolithic to the Roman period, environmental conditions exerted comparable effects on wild and domestic species, though the magnitude and timing of changes varied, reflecting species-specific interactions with humans,” wrote the researchers. 

Meanwhile, researchers said climate change is now accelerating these changes.  

A 2024 study published in Nature Communications predicted that by 2050, tropical fish species will be 14 to 39 percent smaller. 

New Atlas said the results of the study are a warning: “This French study demonstrates that today’s shrinking wild species and ballooning livestock aren’t isolated quirks – they’re part of a long trajectory of human-driven change. Body size is a master trait that affects everything from reproduction to food webs, so consistent shrinkage in the wild is a warning signal for biodiversity and ecosystem stability.”