Animal Size Linked to Cancer Risk in New Research

A new study has overturned a 45-year-old belief about cancer in the animal kingdom, revealing that larger species generally have higher cancer rates than smaller ones. To get to this conclusion, researchers from the University of Reading, University College London, and The Johns Hopkins University School of Medicine examined cancer data from 263 species across amphibians, birds, mammals, and reptiles.

The findings, published in the Proceedings of the National Academy of Sciences (PNAS), challenge "Peto's paradox," which suggested no link between an animal's size and its cancer risk. The study shows that bigger animals consistently have higher prevalence of both benign and malignant tumors.

Professor Chris Venditti, senior author of the study, stated, "Everyone knows the myth that elephants are afraid of mice, but when it comes to cancer risk, mice are the ones who have less to fear. We've shown that larger species like elephants do face higher cancer rates—exactly what you'd expect given they have so many more cells that could go wrong."

Interestingly, the research also found that species that evolved to be larger more rapidly, such as elephants, developed better natural defenses against cancer. Co-author Joanna Baker explained, "When species needed to grow larger, they also evolved remarkable defences against cancer. Elephants shouldn't fear their size—they developed sophisticated biological tools to keep cancer in check."

The study revealed some surprising outliers. The common budgie, weighing less than 30g, was found to have cancer rates more than 40 times higher than expected for its body size. In contrast, the naked mole rat has almost no recorded prevalence of cancers.

According to the team, "Finding which animals are naturally better at fighting off cancer opens exciting new paths for research. By studying these successful species, we can better understand how cancers develop and potentially discover new ways to fight the disease."