Hi.
I have a bit of background in medicine and have been practicing it for a while, and I guess it's time I gave my take on the matter.
Let's set up a hypothetical scenario. Let's say Joe gets infected with Staph Aureus. He takes his medicine, but he suddenly gets worse, and we find that it's because his bugs are now resistant to his antibiotics. There's 2 scenarios why this could have happened, as explained here:
http://evolution.berkeley.edu/evosite/evo101/IIIC1aRandom.shtmlif don't want to read it, the two scenarios are:
1) resistant strains of S. Aureus infected him along with the non-resistant variety in the first place, and the antibiotic killed those susceptible strains, leaving the resistant strains to party hard like a couple of teenagers during spring break
2) the S. Aureus, after being exposed to the susceptible strain, develops mutations and becomes used to the antibiotic, screwing Joe over.
having studied this for many years, I've always been told that number 1 is the correct answer. Joe basically won the unlucky lottery and got infected by a resistant strain. Now how did resistant strains come about in the first place?
Completely at RANDOM, with NO respect to selective advantage.How did they figure this out you ask? Some dude named Lederberg did an experiment on it, 50 years ago. And no study has ever shown to portray the opposite effect.
http://evolution.berkeley.edu/evosite/evo101/IIIC1bLederberg.shtmlso unless some study us universally agreed upon by microbiologists and evo biologists that #2 is actually the correct answer, those who understand otherwise have a flawed (if not misleading) understanding of evolution. I wouldn't blame em, since it really is confusing sometimes.
p.s. and Joe lived happily ever after... just kidding. He spent like 2 months in the ICU, his kidneys shut down and he died of sepsis, leaving his family in debt for like a kazillion years. Yay! /sarcasm