are chain letters alive?

Paul Schlosser SCHLOSSER at
Thu Feb 24 11:26:55 EST 1994

In <2kiga1$rnp at>, jayjay at (Jacob BROSTOFF)
mentions strains of endosymbiotic bacteria that require the host to express
certain genes to survive.  This is a requirment of the environment, and I
presume that the host would be expressing these genes even if the bacteria
were not present.  In that sense, it is different from a chain letter
because forwarding a chain letter is not something that you would do if you
had not received the chain letter - you have to make a conscious decision to
do so.  Does the bacteria ask the host to replicate the bacteria and then
die if the host doesn't wish to do so? I think not.  Thus, the host is the
environment, and as long as the environment stays in approximately the same
state (continues to do what it would do anyway) then the bacteria (or a virus)
will perform a series of actions that, almost certainly, leads to its own
(self) replication.  The propogation of a chain-letter requires a significant
change in (the behavior of) it's environment -- if the environment does not
change (its behavior) at all, then the environment has remained in open set
containing itself, but the chain letter does not propogate.  Thus the "open
set" part of the definition cuts both ways:  the fact that a change in the
environment ceases the propogation does not mean that a structure is not
alive, but if propogation *requires* a change in the environment, then it
is not alive.  Here my use of environment is somewhat loose, but includes the
normal life-cycle of a host or the day/night & seasonal cycles of the earth.
(I'm not quite up to a formal definition of "environment" right now, but
essentially it's a set of conditions and physical surroundings that, while
dynamic, stays within an open set surrounding some closed curve.

schlosser at

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