Study Reveals Drastic Changes in Animal Size Over 1,000 Years

A comprehensive study has uncovered significant changes in animal morphology over the last millennium, showing that domesticated animals have become larger while their wild counterparts have shrunk. Conducted by researchers at the University of Montpellier, this investigation involved the analysis of over 225,000 bones from 311 archaeological sites throughout Mediterranean France. The findings underscore the profound impact of human activity on animal evolution.

The research team meticulously compiled a total of 3,858 records, measuring the length, width, and depth of bones and teeth from a variety of species. This extensive dataset spans an impressive timeline of 8,000 years and includes both wild animals, such as foxes and deer, and domesticated species like pigs, sheep, and chickens. The results indicate a notable divergence in size over time, particularly accelerating in the last 1,000 years.

As human populations expanded and landscapes became increasingly fragmented, wild mammals and birds experienced a general decrease in size. Increased hunting pressure further contributed to this trend. In stark contrast, domesticated animals have grown larger due to selective breeding practices that favour traits enhancing meat, milk, wool, and companionship.

“Our analyses reveal a long-standing synchrony between wild and domestic species until the last millennium, both influenced by a complex interplay of environmental and anthropogenic factors,” the researchers noted. The study highlights that environmental conditions significantly affected both categories of animals during earlier periods, such as the Early Neolithic and the Roman era. However, the magnitude and timing of changes varied by species due to their specific interactions with humans.

To understand the broader context of these changes, the research team also examined environmental data over the 8,000-year span. They looked at climate variations, flora, human population growth, and land use patterns. This modeling allowed the identification of key trends that explain the increasing size of domestic animals alongside the decreasing size of wild species.

Interestingly, the study found that climate change has not been the predominant factor driving these morphological changes. While humans have selectively bred cattle and chickens for increased productivity, they have simultaneously exerted pressure on wild populations through habitat destruction and overexploitation. Nevertheless, climate change is now exacerbating these trends. A 2024 study published in Nature Communications predicts that by 2050, tropical fish may shrink by 14% to 39% due to limitations in oxygen supply for larger individuals.

This phenomenon is echoed in seabird populations. For instance, the Atlantic puffin (Fratercula arctica) has shown a decline in offspring size, attributed to reduced food availability linked to warming waters and a significant decline in krill populations, which have decreased by approximately 50% over the past 60 years. The timing of seasonal insect blooms has also shifted, leaving migratory birds without essential food resources upon their return.

A 2018 biomass study revealed that the combined biomass of humans and livestock now vastly overshadows that of wild mammals. Humans account for approximately 34% and livestock around 62% of total mammal biomass, leaving wild mammals with a mere 4%. This stark discrepancy raises concerns about sustainability and biodiversity.

The findings from the French study illustrate that the ongoing decline of wild species and the growth of domestic animals are not isolated incidents but part of a long-term trajectory driven by human activity. The shrinking body size of wild animals serves as a warning sign for biodiversity and ecosystem stability. Concurrently, the increasing size of domestic animals reflects the unsustainable demands for land, water, and feed.

The researchers emphasized that the evolutionary trajectories of domestic and wild species have diverged significantly since the Middle Ages. “Domestic species experienced intensified human selection, while human activities increasingly impacted wild populations and their habitat,” they explained. The study, published in the Proceedings of the National Academy of Sciences, serves as both a historical reflection and a forecasting tool for ecologists. It highlights the urgent need to rethink our approaches to wildlife conservation and domestic animal breeding practices as we navigate the complex interplay of environmental and human factors shaping the future of animal morphology.