A Science study analyzed 894 dogs from roughly 120 breeds in the Dog Aging Project and generated 1,640 methylomes. The resulting epigenetic clock could estimate a dog's age to within about one year, while larger and male dogs showed faster molecular aging. The strongest body-size differences appeared around LINE1 transposable elements: more than 40% of LINE1-associated regions lost methylation with age, and giant breeds lost roughly 35% more LINE1 methylation per year than small breeds. The work offers a molecular clue for shorter large-dog lifespans, but it does not yet prove that LINE1 change is a cause rather than a consequence, nor can it be directly converted into human therapy. Longitudinal and mechanistic studies are still needed.