Answer:
Hayflick theory
Step-by-step explanation:
According to Hayflick theory aging process is controlled by a biological clock which lie within each living cell. According to this theory human cells have a limited life span.
this theory explain the mechanisms behind cellular aging. It suggests that a normal human cell can only replicate and divide arount forty to sixty times before it cannot divide anymore, and will break down by programmed cell death or apoptosis due to which number of body cells experiencing abnormalities with age.