Hayflick limit

[3][4] Macfarlane Burnet coined the name "Hayflick limit" in his book Intrinsic Mutagenesis: A Genetic Approach to Ageing, published in 1974.

[5] Prior to Leonard Hayflick's discovery, it was believed that vertebrate cells had an unlimited potential to replicate.

To provide required nutrients, embryonic stem cells of chickens may have been re-added to the culture daily.

Hayflick noticed that one of his cultures of embryonic human fibroblasts had developed an unusual appearance and that cell division had slowed.

[9] Hayflick next set out to prove that the cessation of normal cell replicative capacity that he observed was not the result of viral contamination, poor culture conditions or some unknown artifact.

The experiment proceeded as follows: Hayflick mixed equal numbers of normal human male fibroblasts that had divided many times (cells at the 40th population doubling) with female fibroblasts that had divided fewer times (cells at the 15th population doubling).

[3][5][9] These results disproved Carrel's immortality claims and established the Hayflick limit as a credible biological theory.

Phase two is defined as the period when cells are proliferating; Hayflick called this the time of "luxuriant growth".

[citation needed] The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes.

[15] Hayflick suggested that his results in which normal cells have a limited replicative capacity may have significance for understanding human aging at the cellular level.

[clarification needed] Thus, the limited capacity of cells to replicate in culture may be directly relevant to the overall physical aging of an organism.