Hayflick limit

The Hayflick limit or Hayflick phenomenon is the number of times a normal human cell population will divide until cell division stops. Empirical evidence shows that the telomeres associated with each cell's DNA will get slightly shorter with each new cell division until they shorten to a critical length.

The concept of the Hayflick limit was advanced by American anatomist Leonard Hayflick in 1961, 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. Each mitosis slightly shortens each of the telomeres on the DNA of the cells. Telomere shortening in humans eventually makes cell division impossible, and this aging of the cell population appears to correlate with the overall physical aging of the human body.

Australian Nobel laureate Sir Macfarlane Burnet coined the name "Hayflick limit" in his book Intrinsic Mutagenesis: A Genetic Approach to Ageing, published in 1974.

Prior to Hayflick's discovery, it was believed that vertebrate cells had an unlimited potential to replicate. Alexis Carrel, a Nobel prize-winning surgeon, had stated "that all cells explanted in culture are immortal, and that the lack of continuous cell replication was due to ignorance on how best to cultivate the cells". He supported this hypothesis by claiming to have cultivated fibroblasts from chicken hearts and to have kept the culture growing for 34 years. This indicated that cells of vertebrates could continue to divide indefinitely in a culture. However, other scientists have been unable to repeat Carrel's result.

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