Many species of turtles and tortoises have biological mechanisms that slow down or even completely switch off ageing, according to a new study that may unravel secrets to longevity in humans.
The research, published in the journal Science on Thursday, looked at signs of senescence – the gradual process of deterioration of physical and functional characteristics – among tortoises and turtles living in zoos and aquariums.
In the analysis, which also included data from long-term field studies of 77 species from 107 wild populations, including turtles, amphibians, snakes, crocodilians and tortoises, an international team of scientists found that the pattern of ageing in these cold-blooded creatures does not resemble that seen in humans or other animals.
Most of the studied creatures aged slower, and in some cases, their senescence is negligible, scientists said.
Of the 52 species analysed in the study, scientists said three-fourths of them showed extremely slow senescence, while 80 per cent appeared to have slower ageing than modern humans.
“By investigating the nature of [this] variation, something new may be learned about ageing in humans,” gerontologists Steven Austad and Caleb Finch, who were not involved in the study, write in a commentary on the discovery.
Some of the species have the ability to reduce their rate of ageing in response to the improved living conditions in zoos and aquariums, compared to the wild, scientists say.
In biology, some theories predict that senescence starts after sexual maturity as a tradeoff between the energy an organism invests in repairing damages in its cells and tissues, and the energy it invests in reproduction, so its genes are passed to the next generations.
Due to this tradeoff, researchers have held that after reaching sexual maturity, individuals inevitably stop growing and start experiencing senescence – a prediction that has been confirmed for several species, particularly mammals and birds.
Turtles and tortoises, and other organisms that keep growing after sexual maturity, could have the ability to keep investing in repairing cellular damages – reducing and even avoiding the deleterious effects of senescence, scientists say.
However, researchers add that while these creatures show negligible senescence, they are not immortal.
Their risk of death does not increase with age, but it is still larger than zero, scientists say.
Although humans have witnessed unprecedented increases in longevity in the last century, scientists say improved living conditions does not modify the rate of ageing in humans and other primates.
In these species, environmental changes mostly affect infant and juvenile mortality and other age-independent causes of death like predation or extreme conditions, scientists say.