The concept of the Hayflick limit was advanced by American anatomist Leonard Hayflick in 1961,[1] at the Wistar Institute in Philadelphia, Pennsylvania. Hayflick demonstrated that a population of normal human fetal cells in a cell culture will divide between 40 and 60 times. The population will then enter a senescence phase, which refutes the contention by Nobel laureate Alexis Carrel that normal cells are immortal.