Damage to mitochondrial DNA contributes to aging, and mitochondrial function is in general influential upon aging - damage causes harm by preventing the production of protein machinery vital to mitochondrial activity, which is the start of a long process that sees cells overtaken by dysfunctional mitochondria, and exporting their dysfunction to surrounding tissue by emitting harmful reactive molecules. There are numerous different sorts of DNA damage, however. Point mutations, for example, have been shown to do little to aging. Deletions, where whole reaches of DNA are knocked out, are a different story, and here researchers are investigating how this form of DNA damage varies between species: "Deletion mutations within mitochondrial DNA (mtDNA) have been implicated in degenerative and aging related conditions, such as sarcopenia and neuro-degeneration. While the precise molecular mechanism of deletion formation in mtDNA is still not completely understood, genome motifs such as direct repeat (DR) and stem-loop (SL) have been observed in the neighborhood of deletion breakpoints and thus have been postulated to take part in mutagenesis. In this study, we have analyzed the mitochondrial genomes from four different mammals: human, rhesus monkey, mouse and rat ... Our analysis revealed that in the four species, DR and SL structures are abundant and that their distributions in mtDNA are not statistically different from randomized sequences. However, the average distance between the reported age associated mtDNA breakpoints and their respective nearest DR motifs is significantly shorter than what is expected of random chance in human and rhesus monkey, but not in mouse and rat, indicating the existence of species specific difference in the relationship between DR motifs and deletion breakpoints. In addition, the frequencies of large DRs tend to decrease with increasing lifespan among the four mammals studied here, further suggesting an evolutionary selection against stable mtDNA misalignments associated with long DRs in long-living animals."