Joao Pedro de Magalhaes, who maintains the rather excellent senescence.info and associated resources for scientists, has been keeping himself busy with an examination of metabolic rate and life span: "One of the oldest and most popular explanations is the idea that short-lived animals like mice and shrews have high metabolic rates and thus accumulate molecular damage faster than animals with lower metabolic rates, such as elephants. ... The new study, however, disproves this simple, even intuitive explanation by finding no correlation between metabolic rate and longevity using data for several hundred species, the largest dataset ever employed in such an analysis. ... Not only the study disproves the "rate of living" theory, but it also raises doubts regarding another popular theory of aging: the free radical theory of aging, which argues that damage caused by toxic by-products of oxygen metabolism called reactive oxygen species accumulates with time resulting in aging. Because metabolic rates were estimated from oxygen consumption at rest, the study also raises questions of whether damage caused by reactive oxygen species plays a role in differences in longevity between species. ... However, we know that not all things are equal. For example, there could be differences in antioxidant levels that we did not take into consideration."