Re: Sector General Again

In article <q48i52pg3g5raugqfg78ej13hn79of0dig@xxxxxxx>,
David Johnston <rgorman@xxxxxxxxx> wrote:
It seems
superficially reasonable that parasites which developed to fit one
species couldn't bridge the gap into a separately evolved species.

That ... depends. As with several things about the series, as much as I love
it, he didn't bother thinking it out. (An example I've used before: okay, so
they use groups of four-letter classifications to describe a species. Nothing
wrong with that... until you get to an alien race that doesn't doesn't have 26
letters in their alphabet. Or doesn't even *have* an alphabet. But I
digress.)

But then again, quite a lot of the aliens can eat each other's food
and garner nutrition from it normally. Surely that means there must
be some microscopic life forms that will find at least some other
aliens "edible"?

The problem is that there are going to be several types of "parasites."

It seems reasonable that viruses from one planet will be able to infect
another planet's species, even the second planet's life uses DNA. Viruses go
after specific sequences of DNA, and while we do have cross-species viruses
(quite a few, in fact), all of the life on this planet does share a
significant amount of DNA.

But then there are other microscopic parasites. Bacteria, for example, only
need certain substances to thrive. And while some bacteria may attack certain
kinds of organs or cells, usually you have to worry about what chemicals they
produce, or how the immune system deals with them.

Similarly for tapeworms, and amoebae, and other internal parasites. They
might even be *worse*, because the chemicals they produce as part of their
life cycle may have disastrous effects on an alien.

And external parasites were never, I think, even mentioned. Fleas and ticks
will go after anything that smells or glows like it might be food, to pick an
example.

.

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