1961 Hayflick limit

Hayflick limit

• A cell doesn’t live forever.
• Leonard Hayflick showed it divides
• between 40 and 60 times and then dies.
• Which has certain bearings
• for those of us
• who are made of cells.
• In his book on the genetic
• causes of ageing, Macfarlane Burnet
• coined the term “Hayflick limit.”

Replication in a dish

• Most people had thought the reason
• cells in petri dishes eventually died
• was that they didn’t get the right nutrients
• or their dishes became contaminated,
• but otherwise they should live forever.
• Alexis Carrel had kept cells
• from chicken hearts alive for 34 years
• and didn’t admit his daily nutrient solution
• could have contained embrionic stem cells,
• which would have renewed his population.
• But Leonard Hayflick saw signs of ageing
• so he collaborated with Paul Moorhead
• to eliminate non-genetic causes.
• They mixed old male human fibroblasts
• with young female human fibroblasts, keeping
• unmixed populations as controls. In the mixed culture
• any error or virus would affect both male and female cells;
• however, the male cells died well before the female cells.

Senescence

• I feel the time is passing.
• I feel my memory has slipped
• into deeper shadows.
• Everyone is ageing at the same rate,
• I say, but what do I know
• about others’ ageing
• or the fragility of the genome,
• or the accumulation of mutations,
• or antatonistic pleiotropy,
• or the advantages of dying young.
• I’m just a poor sample,
• statistically speaking,
• with a finite chance
• of bucking
• actuarial tables.