Researchers are only just starting to look at the cellular defences and repair mechanisms that keep animals youthful. Longer-lived species tend to have higher levels of this enzyme, for any given metabolic rate. And just this year, a team led by Pankaj Kapahi at the University of Manchester found that cells in long-lived species are more resistant to chemical stress. Using cultured fibroblast cells from a variety of species, from rodents to humans, they measured their survival when stressed by exposure to chemicals. For a given metabolic rate, cell survival rates were highest in those animals that lived longest.
Birds seem to have evolved another cellular defence against ageing.
Exactly how this works, however, is unclear. In theory, another way to resist ageing would be to produce more DNA repair enzymes. These simply identify damaged bits of genetic code and replace the nucleic acids. Our Pleistocene ancestors reduced their risk of predation by evolving language to share survival strategies with one another. Modern medicine has undoubtedly increased average life expectancy, mainly by slashing infant mortality.