Hands made us smarter
I wrote about why man is much smarter than animals.
Do you remember?
That was on account of our hands, because then the brain gets the chance to think of useful new manipulations that help us get through life easier.
That phenomenon has been going on for millions of years.
Example: the forerunner of the monkey was a land animal that went to live in the trees and gradually developed grippers at the end of his limbs to move easier through the canopies. But that same grab power enabled him to pick fruit instead of having to bite it off. With the advantage that he also got hold of fruit that hung too far away from his mouth. His hands did not invent this but his brain did so.
So he became smarter.