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A team of researchers has recently debunked the myth that one year in humans is equivalent to seven in dogs. They have come up with a formula that is based on changes in DNA.
It has been widely believed that for every year a person ages, a dog ages seven years. No one knows where this idea came from, but it has been accepted as truth without question.
However, a team of researchers from the University of California in San Diego (United States), as cited by Science Alert, has published a more scientific version of the story based on the evolution of DNA in the scientific journal bioXriv.
The method is based 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. Through this process, one can determine the age in humans; this is known as an epigenetic clock.
In this way, geneticists Tina Wang and Trey Ideker set out to compare the epigenetic clock of humans with that of dogs. Considering that the lifespan of dogs, depending on their breed, can vary significantly: 6-7 years for some large breeds like mastiffs to as long as 17-18 years for breeds like chihuahuas.
Hence, they chose to use the Labrador retriever dog for the study, as this breed shows a high level of genetic homogeneity, making it easier to identify genetic factors associated with complex traits such as aging. The methylation profiles of Labrador retrievers were compared to those of 320 humans aged between one and 103 years, as well as to those of 133 mice.
According to researchers, when comparing dog methylomes to human methylomes, a non-linear relationship was revealed that translates a dog’s age to 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 = 16ln(dog age) + 31. Here, “ln” represents the natural logarithm. So, you need to multiply the natural logarithm of your dog’s age in years by 16 and then add 31. This will give you the dog’s age in “human years.”
Using this formula, certain milestones align quite well. Seven weeks in dogs corresponds to nine months in humans, the time when baby teeth are erupting in puppies and infants. The average lifespan of the two species also matched up: 12 years for Labradors and 70 for humans.
However, other milestones do not align as smoothly. Dogs, for instance, go through puberty and reach sexual maturity faster than humans, so the period between adolescence and middle age does not quite match up. Nevertheless, the process of methylation in dogs slows down as they age, bringing humans back on par with them.
Even though this formula may not be applicable to all dog breeds, it is true that it is more “scientific” than simply multiplying by seven, as it is based on our epigenetic clock. This information was shared by both El Confidencial and Gizmodo.
