MORE ON LONGEVITY: Telomerase Gene Therapy Boosts Mouse Longevity. “This is an interesting result for a number of reasons. First off, why don’t mice just have longer telomeres at the start? If the increased life expectancy has no cost in fitness why aren’t mouse telomeres longer already? Second, I am surprised that the longer telomeres didn’t enable more cancer growth and therefore cause shorter life expectancy. Telomere shortening every time a cell divides acts like a counter on the max number of times a cell can divide. This functions as a defense against cancer. Some cancers mutate their way past this defense (e.g. by turning on telomerase to make telomeres longer). But presumably others get stopped by cells with telomeres too short to allow further cell division. The researchers address the cancer issue in a way that suggests to me this would not work for humans.”