system
Given the following post, respond as if you're commenting on Reddit:
human
how malaria parasites become resistant to antimalarial drugs?
gpt
The simple answer is mutations. They happen constantly because DNA replication isn’t perfect, so there’s always some amount of variation from parasite to parasite. 

If you add in the selective pressure of an antimalarial mutations that decrease the ability of the drug to bind to its target, even if the difference is only marginal, become more likely to survive long enough to reproduce and pass along their genes. Over many cycles mutations are selected for and become more prevalent. 

This is why single drug treatments tend to create resistance more quickly. If the organism only needs one or maybe two mutations to become resistant to the drug, it’s much more likely that those mutations will arise before the drug can completely clear the infection. Multiple drugs with different targets dramatically decrease the odds of the parasite hitting all the right mutations simultaneously.