An open access paper from Impact Aging: "The Mitochondrial Free Radical Theory of Aging (MFRTA) is currently one of the most widely accepted theories used to explain aging. From MFRTA three basic predictions can be made: long-lived individuals or species should produce fewer mitochondrial Reactive Oxygen Species (mtROS) than short-lived individuals or species; a decrease in mtROS production will increase lifespan; and an increase in mtROS production will decrease lifespan. It is possible to add a further fourth prediction: if ROS is controlling longevity separating these parameters through selection would be impossible. These predictions have been tested in Drosophila melanogaster." Where I think the researchers go wrong here lies in not accounting for how differences in mitochondrial composition might affect the level of damage caused by a given amount of ROS. There is a strong argument that species life span differences have a lot to do with how resilient mitochondria are to damage. But read the paper anyway; it's a good introduction to thinking about the mitochondrial free radical theory of aging.