Hayflick and Moorehead in 1961 observed that non-transformed, embryonic human fibroblasts would only go through a set number of divisions before they arrested growth irreversibly. This is called replicative senescence. This concept has become an interesting phenomena for the fields of aging science and cancer science. This is because long living species have more cumulative population doublings (CPDs) before they reach replicative senescence. The long living tortoise has 110 CPDs while short lived species such as rodents have 15 CPDs.
Guess how many cycles humans have?
Humans have about 50 CPDs!
Content Adapted from Aging & Cancer lecture given Dr. Simon Williams of TTUHSC SOM April 19, 2017. Header image: http://www.path.ox.ac.uk In text image: photo of my grandfather and great grandmother.