Deciphering the reason why people often die at the age of 80

One study explains why humans usually die around the age of 80, while other mammals live much shorter or longer lives.

Scientists found that humans and animals die after accumulating some of the same genetic mutations, suggesting that the rate at which DNA fails is important in determining the lifespan of a species.

There is a huge variation in the lifespans of mammals, from the South Asian rat, which lives for only six months, to the bowhead whale, which can live for 200 years.

In the past, experts used to think that size was the key to longevity. Accordingly, smaller animals burn energy faster, causing rapid deterioration.

Artwork: Asianscientist

However, new research from the Wellcome Sanger Institute (UK) suggests that the speed of gene damage may be the key to survival. Long-lived animals have slow DNA mutation rates regardless of species size.

That analysis helps explain why the naked mole rat, which is 12cm long, lives for 25 years, about the same as a much larger giraffe, which usually lives 24 years. The number of mutations per year for this type of mouse is 93 while that number in giraffes is 99.

In contrast, the common mouse had 796 mutations per year and lived only 3.7 years. The average lifespan of humans in the study was 83.6 years with a mutation rate of 47.

The genetic changes, somatic mutations, which occur in all cells, are largely harmless. But some can lead to cancer or impaired function. Somatic cells are responsible for the formation of tissues and organs in multicellular organisms.

Dr Alex Cagan, study author, said: 'To find a similar pattern of genetic variation in distinct animals such as mice and tigers is surprising.

'But the most interesting aspect of the study was the finding that lifespan was inversely proportional to the rate of somatic mutations. This suggests that somatic mutations play some role in aging."

The authors analyzed genetic errors in stem cells from the intestines of 16 mammalian species. The longer the lifespan of a species, the slower the rate of mutation occurs, they noted.

The average number of mutations at the end of the life cycle of the species is about 3,200. That shows that there are many serious errors that make the body unable to function properly afterwards.

Dr Inigo Martincorena commented: 'Aging is a complex process that results from many forms of molecular damage in our cells and tissues. Somatic mutations have been speculated to contribute to aging since the 1950s, but research remains difficult.

'With recent advances in DNA sequencing technology, we may finally be able to investigate the role of somatic mutations in aging and causing many diseases.