- James Gallagher
- Health and Science Correspondent
According to the study, the lifespan of animals is related to the rate at which their genetic code mutates.
The researchers found that mammals – from tigers to humans – have about the same number of mutations by the time they die of old age.
But short-lived animals tend to run out of their excretions faster, according to an analysis of 16 species.
The discovery helps explain why we age and sheds light on one of the most complex mysteries of cancer, the researchers say.
Experts called the results, obtained by researchers from the Wellcome Sanger Institute, “striking” and “suggestive.”
Mutations are changes that sneak into the instructions for how our body is built and how it works—our DNA.
These mutations have long been known to cause cancer, but whether they have a role in aging has been debated for decades. Sanger’s researchers claim to have provided “the first experimental evidence” to suggest that this is the case.
They analyzed the rate at which mutations occur in species with different lifespans. We studied the DNA of a cat, black and white colobus, dog, ferret, giraffe, horse, human, lion, mouse, naked mole rat, rabbit, rat, ring. tailed lemur and tiger.
A study published in the journal Nature shows that mice undergo about 800 mutations per year during their short life span of just under four years.
The longer animals live, the fewer mutations they undergo each year.
Dogs have about 249 annual mutations, lions 160 and giraffes 99, compared to an average of 47 in humans.
One of the researchers, Dr. Alex Kagan, calls this pattern “amazing” and that it is “really surprising and exciting” that all the animals studied have converged on “approximately 3,200” mutations in their lifetime.
If human DNA mutated at the same rate as mouse DNA, we would die with over 50,000 genetic changes.
“Despite different lifespans, mammals have the same number of mutations at the end of life,” Dr. Kagan told the BBC.
“It’s a number, but what does it mean? For us, this is a mystery,” the researcher continues.
Perhaps the body’s cells reach a critical number of mutations and then die. There are also ideas that “several [cellules] misbehavior” begin to take over vital tissues, such as the heart, with age, so that the organs stop functioning properly.
However, it is unlikely that aging is associated with any one process within the cells of our body.
Telomere shortening and epigenetic changes are also thought to play a role. However, when it comes to mutations, the question arises whether there are ways to slow down genetic damage or even repair it.
The researchers want to find out if this pattern applies to all living things or just mammals. They plan to add fish to the analysis, including the Greenland shark, which can live for over 400 years and is the world’s longest-lived vertebrate.
In the field of oncology, there is a conundrum known as “Peto’s paradox”: why don’t large, long-lived animals have very high rates of cancer?
The more cells you have in your body and the longer you live, the more likely it is that one of them will become cancerous. This must be terrible news for elephants and whales.
“Whales have trillions of cells more [que nous]. They shouldn’t be there because they’ll get cancer before they reach adulthood,” says Dr. Kagan.
Large animals tend to live longer, so a lower mutation rate could help explain the paradox, but the researchers say it’s far from the only explanation.
Naked mole rats and giraffes live about the same age, with the same mutation rate, although giraffes are thousands of times larger.
“One would expect the giraffe’s mutation rate to be even lower, but body size doesn’t matter,” says Dr. Kagan.
Instead, the researchers say, other methods of suppressing cancer should have evolved that could inspire new cancer treatments. Elephants, for example, have more copies of a piece of DNA that suppresses tumors.
Dr. Alexander Gorelik and Dr. Kamila Nakserova of Harvard Medical School say the gap between 47 mutations per year in humans and 800 in mice is huge.
“This difference is staggering given the great overall similarity between the human and mouse genomes.
“These results are sobering.”
Dr Simon Spiro, veterinary pathologist at the Zoological Society of London, says: “Animals often live much longer in zoos than in the wild, so our veterinarians’ time is often spent treating conditions associated with old age.
“The genetic changes identified in this study suggest that diseases of old age will be similar in a wide range of mammals, whether old age begins at seven months or at age 70.”