Cornell biologists believe that a laboratory colonies of rats known as a naked mole-rats (Heterocephalus glaber), some of which are older than 26-year-old, are a perfect example of the evolutionary theory of senescence, or aging. The theory suggests that over time natural selection has acted on the genomes of species to cause their bodies to senesce at a specific rate, for example mice senesce much more quickly than humans, thus there lifespan is much shorter.
Professor Paul Sherman and colleagues report that lab mole-rats have survived for nearly three decades – nearly ten times longer than other similar-sized rodents – although in the wild the rats tend to live for just 10 years or so. Sherman believes that the rats live longer in the lab because they are safer, although he also notes that because they live underground they are relatively safe in the wild as well. One factor thought to contribute to the evolution of a longer life span is that of extrinsic mortality, where death is caused by a force outside the animal’s control, for example being eaten by a predator or run over by a car. According to senescence theory, animals that are better protected against extrinsic mortality evolve genetic traits that make them more resistant to senescence than other animals that lead a riskier life. The theory explains why mole-rats tend to live longer in the wild than other similar-sized rodents – because of their habit, and why they live for even longer in captivity. As senescence happens to all parts of organism at the same time, it strongly suggests that there is no single gene responsible for aging. “Senescence theory tells us why the fountain of youth still eludes us — and probably always will,” Sherman concluded.
SOURCE/REFERENCE: Reported by Cornell University on the 6th November 2002
