How
does human evolution or natural selection relate to the susceptibility of disease?

Natural selection is when species learn to adapt to their environment. They could (1) differential reproduction, that is, not all organisms are able to reproduce to their fullest capacity because nature cannot simply sustain it and (2) acquire genes, that is heredity. Certain characteristics of organisms tend to survive if it continues to strive. If it survives, this trait is passed down to the next generations forgetting the other traits but only the one who could survive the environment. Therefore it is true that natural selection is when ‘organisms inherit advantageous traits, and tend to reproduce more successfully than other organisms’  Of course because an organism adapts easily, so as the bacteria and viruses. They mutate and adapt and becomes a new threat.