Ageing: Forever young?
When a cell ages, it damages its neighbors. So if you kill all the ‘old’ cells, you reduce this damage and, while you do not extend lifetimes, you do keep fitness until the end of your days, at least if you are a special lab mouse in a particular experiment.
Old cells are those which have reached the Hayflick limit (the upper bound on the number of times a cell can multiply, and is about 60 times in humans).
Rats, can’t find my earlier post discussing that mortality is foundational to morality and spirituality. Social obligations and fear of death.