by Sarah Knapton
An elderly gentleman
The mystery of why
humans die at around 80, while
other mammals live far shorter or longer lives, may finally have
been solved by scientists.
Humans and animals die after
amassing a similar number of genetic mutations, researchers have
found, suggesting the speed of DNA errors is critical in determining
the lifespan of a species.
There are huge variations in the lifespan of mammals in the animal
kingdom, from South Asian rats, which live for just six months, to
bowhead whales, which can survive for 200 years.
Previously, experts have suggested that size is the key to
longevity, with smaller animals burning up energy more quickly,
requiring a faster cell turnover, which causes a speedier decline.
But a new study from the Wellcome Sanger Institute in
Cambridge suggests the speed of genetic damage could
be the key to survival, with long-living animals successfully
slowing down their rate of DNA mutations regardless of their size.
It helps explain how a five-inch long naked mole rat can live for 25
years, about the same as a far larger giraffe, which typically lives
checked their mutation rates, they were surprisingly similar.
Naked mole rats suffer 93
mutations a year and giraffes 99.
The study suggests it is the speed of genetic damage
could be the key to survival which helps explain
giraffe typically lives for 24 years.
In contrast, mice suffer 796 mutations a year and only live for 3.7
The average human
lifespan in the study was 83.6 years, but the mutation rate was far
lower at around 47.
Genetic changes, known as
somatic mutations, occur in all
cells and are largely harmless, but,
some can start a cell
on the path to cancer or impair normal functioning...
Dr. Alex Cagan,
the first author of the study, said:
"To find a similar
pattern of genetic changes in animals as different from one
another as a mouse and a tiger was surprising."
"But the most exciting aspect of the study has to be finding
that lifespan is inversely proportional to the somatic mutation
rate. This suggests that somatic mutations may play a role in
The team analyzed genetic
errors in the stem cells from the intestines of 16 species of mammal
and found that the longer the lifespan of a species, the slower the
rate at which mutations occur.
The average number of mutations at the end of lifespan across
species was around 3200, suggesting there is a
critical mass of errors after which a body is unable to
'Ageing is a
Although the figure differed about threefold across species the
variation was far less than the variation in body size, which varied
up to 40,000 fold.
The researchers believe the study (Somatic
Mutation Rates Scale with Lifespan across Mammals) opens
the door to understanding the ageing process, and the inevitability
and timing of death.
Dr. Inigo Martincorena, the senior author of the study, said:
"Ageing is a complex
process, the result of multiple forms of molecular damage in our
cells and tissues.
"Somatic mutations have been speculated to contribute to
ageing since the 1950s, but studying them has remained
"With the recent advances in
DNA sequencing technologies,
we can finally investigate the roles that somatic mutations play
in ageing and in multiple diseases."
The research was
published in the