On the contrary, it's almost entirely mental. The body is just the machine that does the moving; the real work goes on in the brain.
Well yes, but if complexity of movement is one aspect of intelligence, then we're way behind some lifeforms out there. The hummingbird springs to mind, with its tiny brain. Houseflies, with their ability to process information so much quicker than we can. I feel this method is flawed, not least because movement is subconcious, and that conscious thought is where intelligence is at... the awareness of the environment and understanding of what it is.

Our thumb gives us quite an advantage over a dolphin when it comes to manipulation. They can't build a computer, even if they knew how to. They are perfectly evolved for their environment. Are we perfectly evolved for our environment? Arguably.

If this is your criterion...
I thought this was once the criterion of science.