[Falling3]

>Do we understand, completely, at a molecular level, the physical and control systems of bird and insect flight? Or how fish swim? Probably not.

That's an excellent point. But at the same time, we do have some level of understanding of the mechanics of swimming and flying. The same really can't be said of intelligence.

[edanm]

That depends what you mean by intelligence.

We understand enough to build computers that win at chess, to build computers that run financial trading algorithms, to build Google.

I agree that intelligence is in some ways harder to fully define than flight, but that doesn't mean that we don't have any understanding of any parts of it.

[Falling3]

Google's definition (which is a good starting point) of intelligence: "the ability to acquire and apply knowledge and skills."

As far as I know, we have very little if anything in the way of software that accomplishes general learning (not limited to a specific domain).