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Summary: Senescence in a Bacterium with
Asymmetric Division
Martin Ackermann,1
* Stephen C. Stearns,2
Urs Jenal1
Senescence (or aging) is a deterioration of
function with age manifested as a drop in
survival and reproduction (1). A fundamental
question about senescence has not been set-
tled: Which organisms should be senescent,
and which should be potentially immortal?
We present evidence for senescence in a bac-
terium with asymmetric division, supporting
the notion that asymmetry is the key condi-
tion for senescence to evolve (2).
The molecular processes underlying se-
nescence are genetically determined. Why
then is senescence--which imposes a cost on
the individual--not eliminated by natural se-
lection? For most organisms, selection
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