Depends who you ask. Many (I suppose most) would ascribe it to God separating us from the animals. In my search to write these posts, I found (and wrote very briefly in the previous episode I think?) that we were not necessarily the first and only time intelligence could have evolved, and there was a complex nervous system of sorts forming before even animals evolved.

Likewise, humans as they are now were not the only ones in recent history to develop intelligence; Neanderthals are said to perhaps show even more intelligence at the time before interbreeding themselves away into Europeans.

It's not that far-fetched to simply put intelligence down to just being one of many solutions to the environment we adapting to.

Don't forget, our ability to shape the landscape of the earth may make us think ourselves as the most successful species on earth but mites, ants, rats, even wheat have managed to dominate the planet in their own way, covering more terrain than we ever have to date.

They just didn't need the big brain we're so proud of!

But, if an outside influence were to be involved, that just extends the question to where they got their intelligence from, and that would probably be likely through a similar evolutionary process, just earlier in the Universe