Dog Life Miles: How to Find Out How Big Your Dog Is?

If your dog has lived vigorously for 10 years, it is generally believed that the dog has reached old age, which is equivalent to the rare 70 years of human beings. This conversion factor, that is, one year of dog life is equivalent to 7 years of human life, is calculated by dividing the average life span of humans (about 77 years) by the average life span of dogs (about 11 years).

The basic assumption of this algorithm is that at any stage of a dog's life, each calendar year he spends is equivalent to 7 human years. But new research shows it's not that simple. If we look at some basic key stages of canine growth and development, the reasons become clear.

For example, most dog breeds reach sexual maturity between 6 months and 12 months. According to the above traditional conversion, the upper limit of this age for dogs is only equivalent to 7 years of human childhood. At the advanced end of the dog life cycle, although rarer, we know that some dogs can live beyond 20 years. According to the rule of "conversion of 1 dog year equals 7 human years", a dog in his 20s is equivalent to an unimaginable super longevity of 140 years.

To complicate matters further, the length of a dog's lifespan depends greatly on the breed. Smaller dogs live significantly longer, suggesting that small dogs mature and age more slowly than larger dogs.

New research into dog lifespan suggests pet dogs are entering canine middle age much sooner than most of their owners think.

All of the above leads to the question, what exactly do we mean by age? The most obvious way to describe age is the length of time measured in years from birth to the present. This is what is called chronological age.

However, there are other ways to define age. For example, biological age is a definition that focuses more on the physiological condition of an individual subject and mainly relies on the assessment of a person's physiological development indicator characteristics. These include an "aging index" that takes into account an individual's disease status, cognitive impairment and activity level.

In addition, there are more objective biomarkers of aging, such as gene presentation levels (genes produce proteins at different rates at different stages of life) or the number of immune cells. The rate at which biological age increases depends on individual genetic factors, mental health and lifestyle.

For example, if you spend a lot of time eating junk food and smoking, and exercise less and eat less healthily, your biological age is likely to exceed your actual age. Or, if you take care of your physical health, you might be a 60-year-old man with a 40-year-old body.

To measure a dog's lifespan, looking at the dog's DNA methylation levels is a more accurate method than counting the years the dog has lived.

dog life mileage

When comparing the ages of animals across species, biological definitions of age are much more valid than definitions of years. Even if you know that hamsters only live 3 years, you'd still be confused about what stage of life a hamster is in when it's only 6 weeks old. But if you understand that the hamster is old enough to breed, you know that the hamster is mature.

A group of the latest scholars studying the phenomenon of aging in life believe that a reasonable way to measure biological age is to observe the species' "DNA clocks" (epigenetic clocks, which can also be translated as epigenetic clocks). DNA clock refers to a method of measuring the lifespan of organisms based on their DNA methylation levels. The DNA of all mammals changes its genetic appearance over time, showing varying degrees of methylation.

In the first year of a dog's life, they develop very rapidly. When they reach 1 year old, they are equivalent to 31 years old in humans.

DNA "methylation" in particular is the best indicator of biological lifespan. The so-called methylation refers to the biochemical phenomenon in which a carbon atom combined with three hydrogen atoms, a methyl group, is added to DNA. Despite being in different species, many notable physiological markers of development, such as tooth development, appear to occur during the same time period with the same degree of methylation. So by comparing DNA methylation levels in Labrador retrievers and humans, the researchers came up with a scientific formula that corresponds dog age to human age.

The formula is: Human age = 16 × ln (actual years experienced by the dog) + 31.

The ln in this formula represents a mathematical function called the natural logarithm. It is well known that the logarithmic function is often used to calculate the energy released by an earthquake (Richter scale) or to measure the non-linear numerical variation pattern of sound (decibel). Natural logarithms are useful in measuring numbers that vary greatly in quantity. It's even possible to use a logarithmic chart to calculate our perception of the passage of time, thus explaining why we feel that time passes faster as we age.

In the chart below, you can see in the red dashed curve how the natural logarithm converts dog lifespan (dog years) into human years. This curve shows that dogs mature very quickly at first, but their aging then slows down, meaning that most of canine life is spent in a long period of middle age.

An easier way to calculate logarithms is to remember that one year of dog life is equivalent to 31 years of age in humans.

An easier way to calculate logarithms is to remember that one year of dog life is equivalent to 31 years of age in humans. After that, every time a dog's actual age doubles, the equivalent of human years increases by 11 years. So 8 calendar years represents three "doublings" (from 1 to 2, from 2 to 4, then from 4 to 8), which is 31 + 3x11. Therefore, an 8-year-old dog is equivalent to a 64-year-old human.

This useful, simple approximation is the black curve plotted under the red log-transformed curve. The green line represents the unreliable traditional algorithm of "one dog year is equal to seven human years". From the direction of the green line, it can be seen that this algorithm is completely distorted during the highest age period of the dog.

In fact, most dog lovers have begun to suspect that the corresponding age relationship between humans and dogs is non-linear, because they have noticed that in the beginning, their pets mature much faster than the "1 year equals 7 years" algorithm shows speed.

A more sophisticated life experience observation than the "1 year equals 7 years" rule found that the first two years of a dog's life are equivalent to 12 human years, and all subsequent years are equivalent to 4 human years. The blue curve in the figure above represents this particular rule of thumb, which is consistent with the new logarithmic law.

The latest DNA study of human and dog age transitions, shown in a logarithmic table, shows that dogs are entering middle age faster than even most dog owners imagine. What dog owners need to keep in mind is that when you find that your dog Rex is unwilling to jump around and chase balls as usual, your dog may have lived longer than you took for granted.

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