system
Given the following post, respond as if you're commenting on Reddit:
human
Why do bad smells actually smell bad to us?
gpt
We smell different things differently because of the way the particles interact with receptor enzymes in our noses. 

Bad things smell bad because this is beneficial in an evolutionary sense. When you think about what “smells bad” it is often things like faeces or rotten food which are also harmful to humans if consumed or even touched due to illness and disease. 

So it would be beneficial for early man to have a negative reaction to such objects through smell and those who avoided them would be more likely to survive and pass on their genes which has continued to today while the people who enjoyed the foul smells were eliminated by natural selection.