When we search the cosmos for evidence we are not the first advanced life form, we look for things that we could share in common. This anthropomorphism is common in culture, in everything from science studies to science-fiction. And it may not be wrong.
Assuming we have any extra-terrestrial neighbors, far less popular is the idea that we will be the advanced civilization new ones are terrified about being invaded by, they will likely have undergone natural selection just like we did. In the video game Spore, almost everyone evolved creatures that were purple and had huge eyes, despite trying to do things randomly, and that may happen on other planets also.