Pictured above is a sea squirt. What's fascinating about sea squirts is that, similar to a frog, they are tadpoles when they are young, but instead of growing legs, upon adulthood they root themselves into the ground and live the rest of their lives stationary as if they're plants. And as soon as that happens, they eat their own brain.
Why? Simply because once the squirt gives up on movement, snacking on its own brain gives more value than keeping it. Without the ability to move, a brain is worse than dead weight. This is a deep coupling of the mind and the body. It is a living demonstration of the fact that intelligence is only desirable if it's beneficial from an evolutionary standpoint.
Imagine if dogs were as intelligent as humans. Would there be dog civilizations? I don't think so. Humans are the most intelligent species by far for a reason. It is our hands that give us the ability to manipulate and our feet that make us bipedal, freeing the upper two limbs up, that gave rise to our intelligence.