Researchers have recently debunked the myth that one human year is equivalent to seven dog years by developing a formula based on DNA changes. The idea that aging in dogs is seven times faster than in humans has been widely accepted without question, but this new research challenges that belief.
However, a team of researchers from the University of California in San Diego (USA), as cited by Science Alert, recently published a more scientific version of the story based on the evolution of DNA in the bioXriv scientific journal. The method relies on an epigenetic mechanism called methylation. As both humans and domestic dogs age, methyl groups are added to our DNA molecules, which can alter the activity of a DNA segment without changing the DNA itself. This process allows scientists to determine the age of individuals, known as an epigenetic clock.
Geneticists Tina Wang and Trey Ideker aimed to compare the epigenetic clock of humans with that of dogs. Dogs’ lifespans vary significantly depending on their breed, with some large breeds like mastiffs living 6-7 years while smaller breeds like Chihuahuas can live up to 17-18 years. For their study, they chose to use Labrador Retrievers due to the genetic homogeneity in this breed, which increases the chances of identifying genetic factors associated with complex traits, including aging. The methylation profiles of Labrador Retrievers were compared with those of 320 humans aged between one and 103 years, as well as with those of 133 mice.
Researchers found a non-linear relationship when comparing dog methylomes to humans, translating dog years into human years. The similarities were greater when comparing young dogs to young humans, and older dogs to older humans.
This alignment of epigenetic clocks allowed the team to create a formula to calculate a dog’s “human” age: human age = 16 * ln(dog age) + 31. Where “ln” represents the natural logarithm. Simply multiply the natural logarithm of your dog’s age in years (use an online calculator if needed) by 16, then add 31. This will give you the dog’s age in “human years.”
Using this formula, certain milestones aligned well. Seven weeks in dogs correspond to nine months in humans, the time when milk teeth erupt in puppies and babies. The average lifespan of both species also matched: 12 years for Labradors and 70 for humans.
However, some milestones didn’t align as closely. Dogs go through puberty and reach sexual maturity faster than humans, so the period between adolescence and middle age doesn’t match. However, dog methylations slow down as they age, bringing them in line with humans.
While this formula may not be applicable to all dog breeds, it is true that it is more “scientific” based on our epigenetic clock than simply multiplying by seven. (Source: El Confidencial and Gizmodo)