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9 Theory 1: Aging by Program
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.