} >The entire specific immune system is an excellent example of applied
} >evolution
} Indeed, although the term `variation' might be preferable since the
} `competeing' units are not put through a selection sieve and do not have
} descendants as such. The genetic deck shuffling in B cells is a truly cool
Actually they are and they do. T cells are put through two sieves: one
to make sure they respond to self-MHC molecules, and another to make
sure they don't respond to self-antigens in those self-MHC molecules. When
a naive lymphocyte runs into the antigen for which it _is_ specific it
begins duplicating madly, into both memory cells which will be more
sensitive in the future and effector cells which secrete antibody,
cytokines, or kill infected cells (B, helper T, cytotoxic T). This
evolution is not inherited by offspring of the organism (except in
maternal antibodies in a baby, but that's temporary) and the lymphocytes
don't go for radical mutations much, but it is pretty evolutionary, and
on the time scale of baterial evolution.
The fact that every organism gets to have its own evolution, without
sharing, obviously shows room for improvement. Vaccines are on obvious
example. And hopefully we will eventually be able to change or add to
the basic structure, thus thoroughly outpacing the microbes.
} due to their stupendous numbers (permitting each species to try lots more
} moves than Deep Blue), their rapid generational turnover, and their own
} coat-changing. Nesse and Williams, 1995, observe with regard to the
All true; I just wanted to emphasize that our immune systems aren't a
rigid, simply coded structure.
Merry part,
-xx- Damien R. Sullivan X-) <*> http://www.ugcs.caltech.edu/~phoenix
"Bill Gates: the man who avoided changing the light bulb by defining
darkness as the standard."