system
A chat on subreddit /r/NoStupidQuestions
human
There is literally no reason. It was just luck. Some animal was born with a more advanced brain by sheer chance, which gave it a higher level of intelligence, which in turn made it more likely for it to pass on its genes. This continued on and on and the smarter animals survived and the dumber ones died out.
gpt
That's not entirely accurate.  Humans evolved intelligence, or rather big brains capable of critical thinking and planning, because it helped us survive.  

We're not the strongest, fastest, most agile animals, so we have to work together to hunt.  Groups of humans that worked well as a team were more likely to survive and reproduce than those that didn't.

Then, the humans that figured out that basic tools made them better hunters helped them outcompete the humans that didn't.  And thus, the genes of the tool-makers were more likely to survive and reproduce.  Etc etc.

Intelligence is a survival tool, just as horns or spikes or chitin armor is; **that it turned out to be so emergent and prolific as to allow for spaceships and cell phones is the accident, not that we developed intelligence at all.**