I have been thinking about this question for a while, I hope my answer is ok.
Humans are thought to be smart because of our technology, society and communication skills. Though testing this would be difficult to prove using experiments as all test would be designed by humans so therefore biased.
Evolution is a continuing process therefore I believe there could be a smarter species than human, though again would depend how you define intelligence!
I have heard of an intelligence test that could be used for other animals, or even aliens if we ever meet any. I’m not sure that it’s unbiassed though.
I think that artificial intelligences will eventually be more intelligent than humans. I think we will chose to make them part of our brains. The power of computers doubles about every year (for the same price), so I’m pretty sure that there’ll soon be computers with far more power than humans.
That’s called exponential growth.
It means that if you count in powers of 2 (same as doubling) then it looks like this.
That’s just counting 11 numbers, it grows very quickly, and this is how technology is growing.
The world’s two most powerful supercomputers are each thought to be about as powerful as a human brain. http://www.top500.org/
But that doesn’t imply they are intelligent. Fortunately computer programs are also getting more intelligent very quickly.