The researchers came to this conclusion by comparing the function level of the mitochondria in fibroblast cell lines from children under 12 years of age to those of elderly people between 80 and 97. As expected, the older cells had reduced cellular respiration, but the older cells did not show more DNA damage than those from children. This discovery led the team to propose that the reduced cellular function is tied to epigenetic regulation, changes that alter the physical structure of DNA without affecting the DNA sequence itself, causing genes to be turned on or off. Unlike mutations that damage that sequence, as in the other, aforementioned theory of aging, epigenetic changes could possibly be reversed by genetically reprogramming cells to an embryonic stem cell-like state, effectively turning back the clock on aging.