A Great Dane usually lives less than a Chihuahua. But what is the reason?
The difference is not limited to isolated cases. In many breeds, the larger the size of the animal, the shorter its longevity tends to be. However, the age that each individual reaches also depends on their health, care and other factors.
A recent study published in the journal ‘Science’ analyzed the DNA of 894 dogs and found that large dogs age faster at a molecular level.
The researchers studied patterns of methylation, a process that adds small chemical groups to DNA without changing the sequence of its letters. With these data they developed an epigenetic clock, capable of estimating biological age. Thus they verified that aging does not progress at the same rate in all specimens.
The key is in certain chemical marks on the DNA that help keep the so-called “jumping genes” inactive: fragments capable of copying themselves and inserting themselves into other places in the genome.
These mobile sequences, known as transposable elements, normally remain controlled by cellular mechanisms. If they were activated inappropriately, they could interfere with other genetic regions. But finding marks that decrease with age is not the same as proving that these fragments are moving or that they cause disease.
In large dogs, these marks are lost more quickly, and this could promote cellular damage, although it has not yet been proven to explain their lower life expectancy.
The work found associations, not a definitive explanation. In addition, growth, the heredity of each breed and the appearance of certain diseases could also contribute to the observed differences. That is why it is important to separate what the analyzes indicate from what still needs to be investigated.
And the surprising thing is that, when comparing different species of mammals, the opposite usually happens: larger animals live longer.
REFERENCES
Blaise L. Mariner, Brianah M. McCoy, Ashlee Greenier, Layla Brassington, Elizabeth Slikas et al. “Epigenetic aging and transposon dysregulation reflect size-related lifespan compression in dogs”. ScienceOctober 8, 2026.
