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by haldujai 4665 days ago
(Bacterio)phages target bacteria only by nature, there are several mechanisms that prevent them from targeting human cells. They recognize bacterial membranes and not human, their replication mechanisms don't work in human cells and our cells have defenses against them. In short it would take a great amount of evolution to make them target human cells in the order of thousands of years at least due to the several existing barriers.

See: https://en.wikipedia.org/wiki/Bacteriophage

Edit: Just in case someone calls me out on this 'thousands of years' is an educated guess on my part from studying evolution not something I've actually read.
2 comments
tedunangst 4665 days ago
How long did bacteria and penicillin coexist? Thousands of years? Then practically overnight the bacteria decided they needed to evolve...

I don't think evolution always works according to the popular "and then the next giraffe's neck was 1mm longer than its parents'" gradual change model.

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lutusp 4665 days ago
> How long did bacteria and penicillin coexist?

In different places, not an issue. It's only when penicillin is directly applied to a bacterial colony is there any chance for bacterial evolution to take place.

> Then practically overnight the bacteria decided they needed to evolve

You mean, when humans applied penicillin to bacteria on a large scale for the first time? That changed the bacteria's environment, most died, except those naturally resistant. It's classic natural selection.

> I don't think evolution always works according to the popular "and then the next giraffe's neck was 1mm longer than its parents'" gradual change model.

But one can argue that evolution almost never works, on the ground that the vast majority of mutations aren't adaptive. But the argument misses the point that some tiny fraction of the mutations become the entire future species because of increased reproductive fitness.

Also, the "gradual change" you describe normally arises because of the odd beneficial mutation, which, apart from being very improbable, might require many thousands of years to manifest itself.

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j_baker 4665 days ago
Fair enough, but I suspect "thousands of years" of evolution may come very quickly if phages were to be used half as widely as antibiotics are.

Besides that, not all of the cells bacteriophages could harmfully target are human cells. What about the billions of gut bacteria in our digestive tract?

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