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 always thought that was a poor design. Aliens likely would find that disgusting.
What interests me is that I believe all warm blooded animals also share this trait. Not certain that is true but if so, wouldn’t that mean it evolved in a very early period?
Also what I find interesting is that the layout of humans to most animals is the same. A head with eyes then nose then mouth among with the brain behind it. Most of the organs are in similar locations. It seems strange that there would not be more variety.
