Human activity altered animal size for past millennium, study finds

A French study has cast new light on how human activity has shaped the morphological evolution of animals over the last millennium.

Conducted by researchers at the French National Centre for Scientific Research (CNRS), the study reveals a clear trend: domestic animals have grown larger in size, while wild species have become smaller since the Middle Ages.

The researchers found that for the past 1,000 years, human activity has been the dominant factor influencing the size of both domestic and wild animals.

This marks a stark contrast with the previous 7,000 years, during which both groups evolved in a similar, synchronized way—mainly driven by environmental and climatic changes.

According to the CNRS, this unprecedented study provides valuable insight into how animal species have adapted to increasing human pressures, both past and present.

The increase in size among domesticated species—such as sheep, goats, pigs, cows, chickens, and rabbits—is attributed to intense human-driven environmental changes, selective breeding practices, and a pursuit of higher productivity.

In contrast, the reduction in size among wild animals—including deer, hares, and foxes—is linked to intensified hunting, habitat fragmentation, and shrinking natural ecosystems.

Published this week in the journal PNAS, the study is the result of a large-scale, interdisciplinary effort involving bioarchaeologists, climate modelers, and archaeologists.

Researchers analyzed over 80,000 bone measurements from 311 archaeological sites in southern France. These findings were cross-referenced with paleoenvironmental, paleoclimatic, and archaeological data collected over the past three decades.

The CNRS highlights that the study offers a compelling illustration of the growing impact of human societies on animal populations and the environment over time.