whats the evolutionary purpose of rocking back & forth?

so, i have autism (and tourettes and OCD). and when i sit down, i have to rock back and forth. i dont know why, i just do. it makes me feel like ME.

i think a lot of autistics do the same thing. so why did we evolve to rock back and forth? why did we evolve our repetitive stimming loop behaviors? is it so that, when we were guarding the cave as cavemen & cavewomen (and caveNonBinaries) many thousands of years ago, our stims kept us awake so we would be good alert guardskeepers? or maybe our stims were good for early agriculture or somethin?

what do u think?