What is natural selection and how does it work with humans?

It is the process where humans through reproduction over generations change according to the environment. An example would be a human civilization who lived centuries ago. Native civilizations usually lived with a greater proneness to diseases than humans now. The reason they were more prone then than we are now is because of natural selection. The people with poorer immune systems died out from diseases, while the people who lived with better immune systems passed on their better traits through reproduction. Over generations, this makes for a better civilization less prone to disease. This is just one example.

unfortunately its not working in humans..
in other animals predators kill and eat the week, in humans we keep them alive and even allow inferoir members of society to have kids.. go figure