New research reveals that genetics may determine about half of how long we live—far more than previously thought. Credit: Shutterstock What influences how long we live, and how much of that is written in our genes? For many years, scientists believed genetics played only a modest role. Earlier estimates suggested that inherited factors explained about 20 to 25 percent of lifespan differences, and some large studies even placed the number below 10 percent. A new study from the Weizmann Institute