Genetics Shows How to Convert a Dog's Age Into Human Years

The idea that 1 year in a dog's age equals 7 years in human age is wrong.

Posted Jul 09, 2020

Kokostephi — commonswiki CC(0)
Source: Kokostephi — commonswiki CC(0)

So how old is your dog in terms of human years? If you ask that question to your acquaintances I am sure that the vast majority of them will simply take their dog's age and multiply it by 7. Thus a 3-year-old dog is said to be the equivalent of a 21-year-old human while a 10-year-old dog is said to be the equivalent of a 70-year-old human. This is an easy and convenient conversion, but unfortunately it is completely wrong—and researchers say that they now have a formula to convert dog years to human years that actually has some real science behind it.

The old dog-to-human age calculation is based upon a very simple set of assumptions. At the time it was developed the average lifespan of a dog was 10 years, while the average lifespan of a human being was 70 years. So it was thought that we could, in effect, stretch a dog's chronological life span to make it match the human life expectancy, and it is that which gives us the computation that every year in a dog's life is equivalent to 7 years in a human's life.

Any thoughtful person with a knowledge of biology knows that this is a completely nonsensical computation. Consider one very significant age marker, namely puberty (when an individual becomes sexually mature and capable of producing offspring). In human beings this typically occurs between 13 and 14 years of age, while in dogs it usually occurs at around 8 to 10 months. To believe the old dog-to-human age formula means that you must also believe that a dog, who the calculations say is the equivalent of perhaps a 5-year-old child, has achieved the same developmental status as a post-pubescent human.

This newest research comes from the laboratory of Trey Ideker, at UC San Diego School of Medicine and Moores Cancer Center. The first author was Tina Wang, who was doing her doctoral research in Ideker's lab at the time. It is based on a fairly new concept in aging studies that claims that chemical modifications to a person's DNA over a lifetime essentially serve as an "epigenetic clock." One such modification involves the addition of methyl groups to specific DNA sequences and this tracks an individual's "biological age." This biological age incorporates the effects that genetics, lifestyle and disease history can have on an individual's life expectancy. The developmental trajectory of such epigenetic changes for all dogs (no matter the breed) and for human beings is quite similar — only the lengths of their lives are different.

The research team scanned the DNA methylation patterns in the genomes of 104 Labrador retrievers ranging in age from 4 weeks to 16 years. They found that certain groups of genes involved in aging follow a similar pattern of changes during the lives of both species. Based on this data they concluded that dogs and humans have parallel age-related changes in their DNA, with the similarities being most apparent when looking at young dogs and young humans or old dogs and old humans. These new findings show that the pattern of aging in dogs, relative to humans, follows a logarithmic law, suggesting that dogs age much more quickly than we might have previously predicted in the early part of their life, achieving adulthood at a chronologically younger age when they still might look much like puppies.

Based on this data we can give you three methods to compute your dog's age in human years, depending upon how much precision you would like. The most precise method involves the empirical equation that the researchers discovered, which is 16 x ln(dog’s age) +31 = human age, (that is the natural logarithm of the dog’s real age, multiplied by 16, with 31 added to the total.)

You can compute this using any calculator which has the ln function. Simply type your dog’s age. Press ln. Press x and type in 16. Press + and type in 31. Hit the equals sign and there you have it.

However, since some of you might not have a scientific calculator, I've done the computations for you in the table below.

SC Psychological Enterprises Ltd.
Source: SC Psychological Enterprises Ltd.

The table above, while providing the information needed, really doesn't give you a graphic picture of the relationship between a dog's age and a human's age in years. The authors of this research report have provided an alternative way of looking at the data that helps us to visualize what's going on quite a bit better, and you can see it below.

Cell Press
Source: Cell Press

To calculate your dog's age in human years based upon their epigenetic analysis using this graph, you simply find the dog's age along the bottom axis, then trace your finger straight up until you hit the red curve. Now trace your finger straight over to the left axis and you will find your dog's corresponding human age.

One of the nice things about this particular graph is that it shows the aspects of this research that have the most practical significance. This logarithmic relationship between a dog's chronological age and the equivalent human age means that, based on this analysis, dogs move into middle age much more rapidly than most dog owners might have suspected. At one year of age, your dog may still physically have some puppy-like characteristics despite actually being past young adulthood. Dogs seem to enter middle-age quite early, and this period of their life is quite prolonged.

This data also suggests we shouldn't press our dogs too hard. If a 7-year-old dog who is already the equivalent of a human senior wants to lie on the couch and not chase a ball as he used to do, let him be. His clock is running a lot faster than yours.

Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission.

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References

Tina Wang, Jianzhu Ma, Andrew N. Hogan, Samson Fong, Katherine Licon, Brian Tsui, Jason F. Kreisberg, Peter D. Adams, Anne-Ruxandra Carvunis, Danika L. Bannasch, Elaine A. Ostrander, and Trey Ideker (2020). Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. Cell Systems, https://doi.org/10.1016/j.cels.2020.06.006