Cellular senescence might also be an evolutionarily
conserved process. Cells from a variety of mammals,
birds and reptiles have been shown to arrest growth
with a senescent phenotype under various conditions69.
Moreover, ovarian stem cells from the simple organism
D. melanogaster stably arrest growth after several divisions,
and so might undergo cellular senescence70. Even
single-celled organisms, notably the yeast S. cerevisiae,
have been shown to undergo replicative senescence71.
Because telomere shortening does not occur in yeast