A Great Dane is lucky to see its 10th birthday, while a Chihuahua might live to celebrate its 20th. But exactly why smaller dogs tend to live longer than their larger counterparts has long been a mystery. Now, new research suggests the differences may stem, in part, from what’s happening at the molecular level.
A study published October 8 in the journal Science suggests big dogs’ cells age faster because of changes that allow potentially harmful “jumping genes” to move around their genomes, or complete sets of genetic instructions. The work is “fascinating,” Borbála Turcsán, an animal behavior researcher at Eötvös Loránd University in Hungary who was not involved with the study, tells Nature’s Heidi Ledford. Founded in 2014, the project has since enrolled roughly 55,000 canine companions of various breeds.
Scientists analyzed the DNA of 894 pet dogs spanning diverse breeds and body sizes. More specifically, they looked at methyl groups, or chemical tags on DNA that scientists often use as biological markers of aging. Methyl groups are part of the epigenome, chemical changes that regulate gene activity—controlling which genes are turned on or off—without affecting the underlying genetic code.
Factors like diet, exercise, stress and pollutants can alter the epigenome. They also looked at detailed demographic and genetic information. Using correlations between DNA methylation patterns and chronological age, they developed a molecular clock that could predict a dog’s age with a median error of less than one year based on its epigenome.
Analyses revealed that larger dogs tend to accumulate epigenetic changes associated with aging more quickly than small dogs, and that male dogs also tend to accrue these modifications faster than female dogs, even if they were neutered at a young age. In other words, both big dogs and male dogs showed signs of accelerated molecular aging. The study also found that dogs whose biological age was older than their chronological age were at greater risk of early death.
World’s tallest and shortest dogs In 2025, the world’s tallest dog, a 3-foot-3 Great Dane named Reggie, and the world’s shortest dog, a 3.6-inch-tall Chihuahua named Pearl, met up for an adorable playdate. In large dogs, this faster molecular aging trajectory seems to be related to “jumping genes,” also known as transposable elements, or DNA sequences that can move from one location in a genome to another. These rogue sequences can interfere with normal gene function, leading to a variety of health problems, as well as inflammation and aging.
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