Model of how somatic DNA damage and mutations could cause aging. In the young tissue on the left somatic mutations have already begun to accumulate during development (red cells). At old age (right) DNA damage responses have led to cell loss through apoptosis and increased somatic mutation loads. Occasionally a combination of driver mutations may give rise to a neoplastic of hyperplastic lesion. This model is currently used in the lab to test if mutation loads in human tissues rise to levels that could have the deleterious effects observed at old age.