Bats are the only mammals that can fly a great distance, but they have another ability. Many bats live a very long time for an animal their size. European researchers are studying bats to understand why they live so long. They hope to make discoveries aimed at fighting the aging process in human beings. Last week, the group of scientists said they had identified important biological qualities in some bat species. The group studied bat chromosomes, a line of genes found in the nucleus of cells. The scientists were most interested in structures connected to the ends of the chromosomes. They are called telomeres. Telomeres protect the ends of chromosomes, which shorten each time a cell divides. Scientists believe this shortening process causes cells to break down. They say this is what causes aging.