How much do your genes determine how long you'll live? It's a question that fascinates us, and one that's been debated for decades. For years, the answer seemed settled – genes account for about 20–25% of the variation in human lifespan, with the rest down to lifestyle and environment. But a new study published in Science has challenged this view, suggesting the genetic contribution might be considerably higher. The reason, according to the researchers, is that previous estimates failed to