[TheOtherHobbes]

Underrated point wrt intelligence is the extent to which it depends on fine motor control. Whether you're building tools, writing, or speaking a complex language, you need fine motor control to make that possible.

So it's not just brainpower, it's likely a combination of potential brainpower - which many species have/had - and fine motor control, which set up feedback loop that translated a mind/body synergy into practical evolutionary benefits.