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I do like the framing of the issue as a sort of bacterial tragedy of the commons.

> The virulent forms, which descend deeper into the respiratory tract, are actually less contagious. The same goes for bugs such as Hemophilus influenzae and Neisseria meningitidis, which can inflame the protective membranes around the brain and lead to life-threatening cases of bacterial meningitis. In doing so, they risk capsizing their own ship without any hope of boarding a new one.

That the microbes kill the very host they depend on in the process of trying to out-compete each other makes for a nice microcosm (perhaps literally?) of humanity's current treatment of Earth's environment.

Well we are kind of like parasites to Earth:

http://www.bitrebels.com/wp-content/uploads/2011/09/Earth-Ma...

> and, besides, Earth’s microbes could not possibly grow in an alien body.

They'll grow anywhere they damn well please, and if you're lucky it's not underneath a membrane that protects your brain or some other organ.

Microbes should not be seen as animals, but as nanotechnology. A bacteria doesn't differentiate between human's throat and a martian's butt. If there are resources it needs and conditions that don't destroy it outright, it will thrive there.
Many (perhaps most) bacteria are specialized for very specific environments. There's tons of strains that are hard or impossible to cultivate in order to study or measure.

http://jb.asm.org/content/194/16/4151.full

Among infectious bacteria, it's common that they only survive in specific host species.

So for any specific bacteria, odds are they wouldn't find an extraterrestrial life form a nice place. (And viruses are probably right out; I doubt a completely alien genetic system would be hackable by Earth viruses.) But there are so darn many bacteria, probably something would manage to infect a Martian.

"Among infectious bacteria, it's common that they only survive in specific host species."

That may be less true than generally assumed. It was very difficult to find out bacteria X survives in environment Y. Even with ‘cheap’ DNA testing it's still much harder than you might think.

Don't forget we still don’t actually know all of the bacteria thrive in the human intestines. The wider ecology of Microbiology is almost a blank slate.

Thanks for the link! I always thought that we know how to cultivate every bacteria we've met. I learned something very interesting today :).
There have been some recent advances, notably in soil bacteria. For example: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC127570/ (you can also find some more popular accounts if you look around.)

We'll probably be making advances in that area for a long, long time, what with the number and variety of microorganisms out there.

> A bacteria doesn't differentiate between human's throat and a martian's butt.

I'm not sure that a spider does either.

Beware the Martian Buttspider, for it also thrives in the human throat.
"We assume that microbes evolved to attack humans when actually we are just civilian casualties in a much older war"

Did anyone actually have this assumption?

First, the claim is not that microbes evolved in response to humans. They appeared much before us. The assumption presented here is that some microbes have evolved in ways, recently, that let them (also) attack humans.

Second, yes, it is very natural for us to assume that when we see an effective reproducing pathogen that affects us, that it has evolved to attack us. That is the case with most viruses affecting humans, as the article mentions - everything in the article about coincidence has nothing to do with viruses. (Sometimes a virus is zoonotic, i.e. originated in another species, but has then adapted significantly to us.)

To be effective against humans, typically the pathogen needs to evolve to do so. That is a very reasonable assumption, and yes, we have been making it, and for rational reasons. Interestingly, it turns out that for some bacteria, it is not the case, as the article shows.

There are plenty of parasites that have the host's death as an essential part of their lifecycle.
Well, yes. I did and I appreciate this correction. Another fine example of the fact that correlation is not necessarily causation. One our old brains are incredibly prone to overlook.
This reminds me of a passage in The Andromeda Strain. I don't have the book here to do an exact quote, but it mentioned that, just as a person easily killed by bacteria was a failure (in that they wouldn't live long enough to reproduce), a bacterium that killed its host was also a failure, because it must die when the host dies. The most successful bacteria are those that can live off a host without killing them, and the most successful hosts are those that can tolerate the presence of bacteria, or even make them work for the host.
-- The most successful bacteria are those that can live off a host without killing them

E.g. Tuberculosis

I was particularly taken by this passage near the end: "There is something unsatisfying, almost nihilistic, about this idea. It deprives us of answers". It got me thinking about the big mistake that we often make about evolution: that it has a purpose, a goal. The idea that evolution involves progress is as old as Darwin, as can be seen in the "March of Progress" illustration showing a parade with a chimpanzee, then pre-humans, then caveman hunter, then modern man. We have been reminded many times that the illustration is too suggestive, but the idea refuses to die. It's very hard to accept that evolution is full of accidents, and that as a species there is nothing remarkable or inevitable about us.

Similarly, there is nothing special about many microbes that cause illness, but it's hard to accept the idea. It's surprising that streptococcus pneumoniae isn't trying to kill us at all, but merely trying to outcompete hemophilus influenzae in our noses, and sometimes the mechanism that aids its struggle ends up preventing our immune system from killing it. We walk into a fist-fight between strangers, and end up hurt ourselves.

Hell, the phrase "trying to outcompete" contains teleological assumptions which the author himself can't escape from. Those dueling bacteria aren't "trying" to do anything. They accidentally mutate, and circumstances make them more or less successful at increasing their numbers relative to the other species.

It's hard to avoid seeing purpose in the living world around us, even when we know it doesn't know us or care about us.

The question of why pathogens kill their hosts has been with me for at least 50 years. At last a cogent answer.