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WHY do we die?

Mary K. Kuhner mkkuhner at phylo.genetics.washington.edu
Tue Oct 24 09:35:55 EST 1995

Could it have to do with the power struggle between single cells and the
organism as a whole?  In a uni-cellular or colonial organism, each cell
is concerned with surviving, reproducing, and having many descendents.
Such a concern is anathema to the survival of a true multicellular
organism--it's allowed to the germ cells, but to no others (in animals;
plants manage quite differently, but on the whole do less cell-type
specialization).  Putting a replication limit on those cells which are
allowed to replicate at all says, in effect, "You've got to support the
group (the organism as a whole) because you have no future as an
individual."  Perhaps this was, in essence, a "political" decision early
in animal evolution--buy some security from rebellion at the cost of
limiting the lifespan of individual cells.    It might be analogous to
the sterility of workers among the social insects.   Worker bees
occasionally manage to lay a few eggs, but the other members of the hive
generally kill them--worker egg-laying may offer advantage to the
individual worker, but it's not good for the group.

It might also be hard to design a working nervous system with permanent
storage without having to have irreversibly specialized cells--
and shutting off division with its chance to get rid of errors pretty
much guarentees eventual mortality.  A single-celled organism can deal 
with DNA errors it cannot repair by splitting into two daughters, one
carrying the error and one hopefully not, so that the error can die
without taking the rest of the genome with it.

If your personality, identity and memory depend on the exact details of
connections among neurons, the technical challenge of adding new neurons
during adulthood might be very, very difficult.  

Mary Kuhner mkkuhner at genetics.washington.edu
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