Bacteria, Penicillin and Evolution
Alexander Fleming discovered penicillin in 1928, and at the time it was a great discovery that helped save countless numbers from death. But bacteria was quick to evolve.
At first, the penicillin was extremely effective against bacterial infections. Where before a slight scrape of a rusty nail or injury might lead to death, penicillin soon became the easy way to make sure that injuries didn't become infected.
However, natural selection kicked in. Natural selection is when individuals in a species are naturally more suited to live in the chosen environment - and therefore breed more and survive better than their weaker neighbors.
In the case of bacteria, natural selection meant that while most bacteria were killed off by the penicillin - a few lucky ones found they were able to survive it. Those bacteria then created more bacteria, and soon a new species of bacteria was developing - one that didn't mind a penicillin environment at all.
What used to be a 'very rare mutation' of a normal bacteria strain is now THE normal makeup for the new, penicillin-resistant strain. Evolution and natural selection both were responsible for how bacteria and penicillin have interacted in the past 85 years and the changes that have resulted.
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