Interesting read. (via Daniel Lemire)

Though we age, it is unclear how our bodies keep track of the time (assuming they do). Researchers claim that our blood cells could act as time keepers. When you transplant organs from a donor, they typically behave according to the age of the recipient. However, blood cells are an exception: they keep the same age as the donor. What would happen if we were to replace all blood cells in your body with younger or older ones?