14.1.3 14.13: Can we slow down the process of aging?

Life extension is possible. Real, honest-to-goodness doubling of the normal life span. Not only is it possible, researchers have demonstrated it repeatedly…in fruit flies.

The results of these life-extension studies are astonishing, but the methods by which they were achieved are simple. Researchers kept several large populations of fruit flies in cages in the laboratory. The flies would feed and lay eggs on a small plate of food. Every few days, a fresh plate would be put in the cage and the old one discarded. At 2 weeks, eggs were collected and used to start the next generation of flies. Propagated in this way, the fly populations were maintained for hundreds of generations. When the longevity of flies in these populations was measured, the researchers found that the flies started to experience the physiological breakdowns associated with aging after a few weeks, and after about a month the flies died.

One researcher thought that changing the force of natural selection on the flies might produce an evolution in their aging pattern. So, instead of collecting eggs at 2 weeks to start the new generation, he cleverly waited longer and longer (FIGURE 14-21). The first new generation had parents that had lived for 3 weeks. If any fly carried a mutation that caused it to die between 2 and 3 weeks, that fly did not contribute to the next generation and that mutation was not passed on.

After several generations, eggs were collected at 4 weeks instead of 3 weeks. At this point, all the flies making up the new generation had parents that had survived for 4 weeks. Any flies that died before 4 weeks of age didn’t contribute to the new generation. Natural selection was now able to reduce the prevalence of mutant genes responsible for early aging.

The experiment continued, progressively increasing the generation time to 5 weeks, then 6, 7, and ultimately 10 weeks—equivalent to decreasing the hazard factor of the fly population. At this point, only those flies with a genome free of mutations that might cause death in the first 10 weeks of life could contribute to the new generation.

The net result was the creation of a population of flies with much “cleaner” genomes. When put under ideal conditions outside the cages, these “super” flies did not experience aging until long after the original flies would have died. In fact, the average life span of the flies hatching from eggs harvested from parents of 10 weeks of age was more than 60 days—double that of the original flies!