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.
In science that is called symmetry breaking (going from a homogeneous blob to left right something) and a very active topic of Research.