AFAIK it all boils down to the fact that during embryonal development our cells, which at that point were just a blob of undifferentiated autonomous chemical machines, somehow managed to unanimously agree upon the cardinal directions (up-down, left-right, front-back) for future development - and thanks to this, we don’t have toes growing out of our ears.
I mean, that’s what dna is for. These machines aren’t operating blindly (or even “cooperating” or agreeing on anything, really). They’re following the code that makes up who we are.
Those who don’t usually don’t make it far.