- The correlation between dog years and human years is non-linear
- This throws the 7-year ratio out of the window
- Researchers' new equation using methylation could be used in multiple species
Think you can calculate your dog's human age by multiplying by seven?
Wrong, according to research published in Cell Systems. Instead of the age-old formula, the correlated rate at which humans and dogs age is non-linear. Humans and dogs don't go through the various life stages at the same pace.
A pre-print was made available last year, but the peer-reviewed paper was only published this week.
The researchers explored how methylation – the process of DNA changing throughout life – could be used as an age calculator across species.
The best part? The researchers got to play with 104 Labradors across a 16-year range to conduct their research, regularly drawing blood for analysis.
In humans, you can use epigenetic clocks to determine age. This is basically a biochemical test that analyses methylation to gauge age, but scientists haven't been able to replicate this test successfully in other mammals.
Researchers decided to turn to dogs as the model species, aligning their methylation stages to humans. There are more than 450 dog breeds that share our human environment as pets and "colleagues".
This means their exposure to external factors is similar to ours, including lifestyles that can impact methylation. Their lifespans are, however, shorter than ours, making the ageing process easier to quantify. Their epigenetic clocks have also been studied before.
How our ageing stages compare
The researchers then compared the methylation changes in dogs and humans of the same age, to determine whether the rate of change remains constant. These included the following stages: infant, juvenile, adolescent, mature, and senior.
"Comparison of each dog methylome to its nearest human counterpart reveals a conserved but nonlinear progression of epigenetic changes, with rapid remodelling in puppies relative to children, which slows markedly in canine adulthood," says the study.
Basically, a puppy at eight weeks is similar in development to a nine-month-old human baby, while a 12-year-old labrador is on the same level as a 70-year-old human. In between, however, the rate is inconsistent.
You can see the correlation between a dog's life and a human in this delightful graph featuring actor Tom Hanks:
This new system means that scientists can now universally figure out the "real" ages of multiple species. They were able to apply their development clock to mice as well.
"While the biology of ageing has historically been considered as separate from that of development... their strong association, demonstrated here, supports a model in which at least some aspects of ageing are a continuation of development rather than a distinct process."
It could also provide some insight into creating ageing interventions to increase lifespans – including those of our beloved pooches.
Image credit: Pixabay