- By James Gallagher
- Health and Science Correspondent
According to a study, the lifespan of animals is related to the mutation rate of their genetic code.
Researchers have found that mammals – from tigers to humans – have about the same number of mutations when they die of old age.
But short-lived animals tend to exhaust their allotment faster, according to analysis of 16 species.
According to the researchers, this discovery helps explain why we age and sheds light on one of cancer’s most complex mysteries.
Experts said the results obtained by researchers at the Wellcome Sanger Institute were “amazing” and “thought-provoking”.
Mutations are changes that creep into the way our body – our DNA – is built and works.
These mutations have long been known to cause cancer, but whether they are important in aging has been debated for decades. The Sanger researchers claim to have produced “the first experimental evidence” to suggest this is the case.
They analyzed the rate at which mutations occur in species with different lifespans. They examined the DNA of a cat, a black-and-white colobus monkey, a dog, a ferret, a giraffe, a horse, a human, a lion, a mouse, a naked mole rat, a rabbit, a rat, a ring-tailed lemur and a Tiger.
The study, published in the journal Nature, shows that mice undergo nearly 800 mutations a year during their short lifespan, which lasts just under four years.
The longer animals live, the fewer mutations they go through 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 Cagan calls this pattern “striking” and that it is “really surprising and exciting” that all of the animals studied have “about 3,200” mutations in their lifetime.
If human DNA mutated as quickly as mice did, we would die with more than 50,000 genetic changes.
“Although they have different lifespans, mammals have the same number of mutations at the end of their lives,” said Dr. BBC’s Cagan.
“It’s the number, but what does it mean? It is a mystery to us,” the researcher continues.
It could be that the body’s cells reach a critical number of mutations and then die. There are also ideas that “a few [cellules] Malfunction” begins to take over vital tissues such as the heart as we age, causing organs to malfunction.
However, it is unlikely that aging is due to a single process in the cells of our body.
Telomere shortening and epigenetic changes are also thought to play a role. However, when mutations are involved, one wonders if there are ways to slow or even repair the genetic damage.
The researchers want to see if this pattern applies to all living things or just to mammals. They plan to include fish in the analysis, including a Greenland shark that can live over 400 years and is the world’s longest-lived vertebrate.
The Paradox of Cancer
There is a conundrum in the field of oncology known as the “Peto paradox”: Why don’t large, long-lived animals have very high rates of cancer?
The more cells there are in your body and the longer you live, the more likely it is that one of them will become cancerous. This should be terrible news for elephants and whales.
“Whales have trillions more cells [que nous]. They shouldn’t exist because they would get cancer before adulthood,” says Dr. Cagan.
Large animals tend to live longer, so their slower mutation rate might 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 similar mutation rates, although giraffes are thousands of times larger.
“You would expect the giraffe’s mutation rate to be even lower, but it’s like body size doesn’t matter,” says Dr. Cagan.
Instead, the researchers say, other methods of suppressing cancer must have evolved that could inspire new cancer treatments. For example, elephants have more copies of a DNA fragment that suppresses tumors.
dr Alexander Gorelick and Dr. Harvard Medical School’s Kamila Naxerova says the gap between a human’s 47 mutations per year and a mouse’s 800 is huge.
“This difference is surprising given the high overall similarities between human and mouse genomes.
“These results are sobering.”
dr Simon Spiro, Veterinary Wildlife Pathologist at the Zoological Society of London, says: “Animals often live much longer in zoos than they do in the wild, so our veterinarians’ time is often devoted to treating age-related diseases.
“The genetic changes identified in this study suggest that diseases of old age are similar across a wide range of mammals, whether age begins at seven months or 70 years.”