- There is strong evidence supporting the suggestion that aging is in some manner programmed into each species, including humans.
- This may be controlled neurologically or hormonally through the hypothalamus.
- Other studies suggest that aging is controlled by the thymus.
- The gland atrophies at about the onset of adolescence. This implies that aging occurs more readily in the absence of the thymus gland.
- In studies cultured cells of a specific type divided a consistent number of times. This implies that the cell’s life cycle is controlled within the cell, rather than externally by the hypothalamus or thymus.
- Scientists agree that although normal cells may have a limited number of times they can divide this is only rarely, if ever, reached in the body.