Scientists compare genomes of 16 species, including humans, mice, and giraffes
Genetic mutations were caused by similar mechanisms in all species
However, animals that deposited them more quickly had a shorter lifespan.
Humans have a longer lifespan than our pet friends
It’s a mystery that has puzzled scientists for years – why do different animals have so many different lives?
While humans can live to be around 80 years old, giraffes die at 24 and naked mole rats at 25, suggesting that something beyond body size is to blame.
To help unravel this mystery, researchers at the Wellcome Sanger Institute compared the genomes of 16 species, including humans, rats, lions, giraffes, and tigers.
Their findings suggest that animals with slower rates of genetic changes – known as somatic mutations – have longer lifespans.
Somatic mutations occur naturally in all cells throughout an animal’s lifetime, with humans acquiring about 20–50 mutations per year on average.
While most somatic mutations are harmless, some can impair cell function or even start a cell on its path to cancer.
A role for these mutations in aging has been suggested since the 1950s, but until now, it remains difficult to observe them in practice.
One of the main long-standing questions has been the ‘Peto’s paradox’, which questions why larger animals do not have a higher risk of cancer despite having more cells.
In the new study, researchers used whole-genome sequencing on samples from 16 mammals that had a wide range of lifespans and body sizes – black and white colobus monkey, cat, cow, dog, ferret, giraffe, harbor porpoise , horse, human, lion, rat, naked mole-rat, hare, rat, ring-tailed lemur and tiger.
Their analysis showed that somatic mutations were caused by similar mechanisms in all species, including humans.
They also accumulate linearly over time, with species with higher rates of mutation having shorter lifespans.
For example, giraffes, which can grow up to 18 feet tall, were found to have a mutation rate of about 99/year and a lifespan of about 24.
Meanwhile, naked mole rats, which are significantly smaller at just five inches, have a similar mutation rate of 93/yr and a similar lifespan of about 25.
“It was surprising to find similar patterns of genetic changes in animals that differ from each other,” said Dr. Alex Cagan, who led the study.
But the most exciting aspect of the study is the finding that life span is inversely proportional to somatic mutation rate.
‘This suggests that somatic mutations may play a role in aging, although an alternative explanation may be possible.
‘In the next few years, it will be attractive to extend these studies to even more diverse species, such as insects or plants.
Unfortunately, the findings did not answer Peto’s paradox.
After accounting for lifespan, the team found no significant association between somatic mutation rates and body mass.
This suggests that other factors must be included in the ability of large animals to reduce their cancer risk.
The fact that differences in somatic mutation rates are explained by differences in lifespan rather than body size suggests that although adjusting mutation rates seems to be an excellent way to control cancer incidence across species, evolution has not really chosen this path,’ said the study author Dr. Adrian Baez-Ortega.
It is quite possible that each time a species evolves to a larger size than its ancestors – such as giraffes, elephants, and whales – evolution may come up with a different solution to this problem. We will need to study these species in more detail to detect them.
Researchers hope the findings will help unravel the mystery of what causes aging.
Study author Dr. Inigo Martincorena said, ‘Aging is a complex process, which results in many forms of molecular damage in our cells and tissues.
Somatic mutations have been speculated to contribute to aging since the 1950s, but they remain difficult to study.
‘With recent advances in DNA sequencing technologies, we can finally investigate the roles that somatic mutations play in aging and many diseases.
This diverse range of mammals end their lives with similar mutations in their cells, an exciting and interesting finding.