Can get new functions for free. Language too has probably paid for improvements in brain machinery for planning ballistic movements like accurate throwing, itself originally developed through hunting payoffs. Brain things are multifunctional. Structured thought s objective aspects Best examples from language but carries over to planning, games, music. Protolanguage limited to short sentences which don t require structuring.
Syntax allows very long sentences, all sorts of contingencies and qualifications.
I think I saw him leave to go home. Not just speak but think in a structured way. Think before speak. Curbs cuts used for lots of things besides wheelchairs, same with brain s machinery for planning movements and hearing sequences. Coherence-finding is very rewarding.