In gerontology, comparative biology of longevity offers a powerful observation point thus far underexploited. We use this approach to evaluate the role of genetic stability in longevity determination, extrapolating existing data from the literature. Screening eight pre-existing studies, we collected data from 47 mammalian species and analyzed the relationship of spontaneous micronucleated erythrocyte frequency to species maximum longevity and species adult body mass. Since in 26 of these species the spleen removes micronucleated erythrocytes from the peripheral circulation, we conducted further comparative analysis on the remaining 21 species. We demonstrate that spontaneous micronucleated erythrocyte frequency correlates primarily with body mass and not with maximum longevity. We suggest that other data on genetic stability could be collected from published works in different species and analyzed in a similar way to test further the role of genetic stability in aging.