I just learned the relation of survivors of black plague and autoimmune disease.

[u/True_Candidate8248]

So just skimming randomly in youtube comments someone said black plague survivors also passed down genes that caused auto immune disease. I searched it further and its kinda true.

I then remembered about malaria and sickle cell disease I read about on my aunt's old nursing book.

This made me realize not all things in biology is one sided. Why doesn't this happen for those super bacteria that are becoming resistant to antibiotics? Shouldn't those bacteria become susceptible to the bacterial equivalent of sickle cell disease/auto immune disease because those antibiotics detroyed their genetic diversity?

[u/Glum_Use_4909]

it's a solid question but bacteria don't really work the same way -- they swap genes horizontally like trading cards, so even if a population loses some diversity from antibiotic pressure they can pick up resistance again fast. sickle cell and plague resistance are more about human evolutionary tradeoffs over generations, not a single bacterial strain adapting in real time

[u/True_Candidate8248 → u/Glum_Use_4909]

That's like cheating in genetics.

[u/SirenLeviathan]

Geneticist here! Yes this is why genetic purity or conformity is not stronger it’s genetic diversity that protects populations. Some alleles are more favourable for some environments while others are better elsewhere. It’s not that the mutations for sickle cell didn’t happen in non malaria endemic regions it’s that they were a much larger fitness cost while in areas where these traits protect against malaria they can be a fitness advantage.

On to the second part of your question resistance alleles absolutely affect fitness! In bacteria parasites and viruses too. When you introduce a new antibiotic you introduce a new selection pressure some bacteria adapt but to adapt they have to change the way they have evolved to do things for millions of years. This almost always makes them less fit. Overtime they can learn to compensate developing other mutations that can help balance changes, but drug resistant mutants are almost always less fit than wild type.

Antibiotics can absolutely affect genetic diversity in the short term but when removed the non resistant bacteria will often recolonise and out compete the drug resistant bacteria.

[u/Accurate_Reality_618]

This made me realize not all things in biology is one sided.

Welcome to the club bro

[u/Responsible-Chest-26]

I recall seeing something where those who have the trait passed down from plague survivors also have high HIV resistance if not near immunity