Unpublished draft

Hayflick–Moorhead experiment

The Hayflick–Moorhead experiment was a 1961 study of normal human fibroblasts in culture that established a finite replicative lifespan for these cells. Leonard Hayflick and Paul Moorhead grew human fetal lung fibroblasts through serial passages and counted the divisions until the cultures stopped expanding, at roughly fifty population doublings. The arrested cells stayed alive and metabolically active, a state now called cellular senescence. The result replaced the prevailing view that normal animal cells divide indefinitely, and it turned the division count into a measurable phenotype that aging research could study.12

Background

Early tissue-culture work produced cell lines that appeared to grow indefinitely, and the