system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do humans have phobias

I have noticed that there are many different phobias but some of them don't make sense to have as a survival instinct like clowns. Does anybody know why we have phobias for survival and others for random thing.
gpt
If you have an experience which makes you genuinely afraid for your life then you pick up on features of the environment that serve as a trigger to that danger.  People tend to unconsciously fixate on things that are novel to them.

An easy example is that you go to a party and you eat some caviar on toast and you've never eaten caviar before.  Then you become violently ill.  You're more likely to develop an involuntary acquired nausea response when exposed to caviar (because it's unfamiliar to you) than to toast (because you've eaten this many times before and know it's benign).

Similarly if someone is raped by someone wearing a leather jacket they may acquire a phobia against any exposure to someone wearing a leather jacket.  They rationally know that leather jackets have nothing to do with them getting raped.  

But we are hard wired to acquire involuntary phobias to things we associate with danger, especially if they are novel, regardless of how rational this is.

It's an evolutionary advantage to avoid anything that we associate with a threat to our life.  Again, regardless of how rational that is.