How human interaction drove evolution to make bears less aggressive

A new paper in Molecular Biology and Evolution, published by Oxford University Press, reports that Italian bears living in areas with many villages evolved and became smaller and less aggressive.

Humans have long shaped the environments in which they live, dramatically affecting ecosystems and biodiversity. Habitat change and overuse are among the human activities with the greatest impacts on wildlife, often leading to population declines and/or shifts in selective pressures, thus influencing how a species evolves.

The Apennine brown bear, Ursus arctos marsicanus, is a small and isolated population found only in Central Italy, with a long history of closeness to human communities. Previous research indicates that this population diverged from other European brown bears 2000-3000 years ago and has remained completely isolated since Roman times. “One major cause of decline and isolation,” said the paper’s lead author, Andrea Benazzo, “was probably forest clearance associated with the spread of agriculture and increasing human population density in Central Italy.”

Today, the Apennine brown bear population shows significant phenotypic differences compared with other brown bear populations. They have smaller bodies, unique head and facial features, and less aggressive behavior than European, North American, and Asian brown bear populations.

Researchers here focused on the recent evolutionary changes driven by human activities on this isolated and endangered bear population. They generated a high-quality chromosome-level reference genome for the Apennine brown bear and re-sequenced whole-genomes from a sample of individuals. These were compared with genomes from a larger European population in Slovakia, as well as previously published genomes of American brown bears.

They characterized genomic diversity and identified adaptation signals distinctive to this population. As expected, Apennine brown bears exhibited reduced genomic diversity and higher inbreeding compared to other brown bears. “More interestingly, however,“ added Giulia Fabbri, another author of the study, “we showed that Apennine brown bears also possess selective signatures at genes associated with reduced aggressiveness.”

The findings suggest that selection on behavior-related genetic variants, likely driven by the human removal of more aggressive bears, resulted in the emergence of a much less aggressive bear population. This illustrates how human encroachment into natural areas led to demographic decline and genomic erosion, increasing extinction risk, yet unintentionally promoting the evolution of a less conflictual relationship between humans and bears.

“The general implications of our findings are clear,” concluded Giorgio Bertorelle, another researcher involved in the study, “human-wildlife interactions are often dangerous for the survival of a species, but may also favor the evolution of traits that reduce conflict. This means that even populations that have been heavily and negatively affected by human activities may harbor genetic variants that should not be diluted, for example, by restocking.”

The paper, “Coexisting with humans: genomic and behavioural consequences in a small and isolated bear population,” is available (at midnight on December 15^th) at https://academic.oup.com/mbe/article-lookup/doi/10.1093/molbev/msaf292.

Direct correspondence to: 
Andrea Benazzo
Department of Life Sciences and Biotechnologies
University of Ferrara
Ferrara, ITALY
bnzndr@unife.it

To request a copy of the study, please contact:
Daniel Luzer 
daniel.luzer@oup.com